a novel environment friendly and efficient gaseous insulator
TRANSCRIPT
A Novel Environment Friendly and Efficient
Gaseous Insulator
Submitted by;
Hafiz Shafqat Abbas
2014-PhD-Elect-012
Supervised by:
Prof Dr. Muhammad Kamran
Department of Electrical Engineering
University of Engineering and Technology Lahore, Pakistan
2020
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A Novel Environment Friendly and Efficient
Gaseous Insulator
Submitted to University of Engineering and Technology, Lahore
In partial fulfillment of the requirement for the award of the degree of
Doctor of Philosophy (Ph.D)
In
Electrical Engineering
Submitted by;
Hafiz Shafqat Abbas
2014-PhD-Elec-012
Thesis approved onâŠâŠâŠâŠâŠâŠ.
âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ âŠâŠâŠâŠâŠâŠâŠâŠâŠ..
Internal Examiner External Examiner
âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ âŠâŠâŠâŠâŠâŠâŠâŠâŠ..
Chairman Dean
Department of Electrical Engineering Faculty of Electrical Engineering
Department of Electrical Engineering
University of Engineering and Technology Lahore
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a. From within the Country
i. Prof. Dr. Muhammad Akbar
Dean, Faculty of Electrical Engineering,
GIK Institute of Engineering Sciences and Technology,
Topi 23640, District Swabi, Khyber Pakhtunkhwa.
Email: [email protected]
ii. Dr. Salman Amin.
Associate Professor.
Department, Electrical Engineering (Taxila)
Email: [email protected]
b. From Abroad
i. Prof. Dr. Koksal Erenturk
Prof. and Chair of the High Voltage and Power Division,
Department of Electrical and Electronics Engineering,
Ataturk University College of Engineering, Erzurum, Turkey.
Email: [email protected] , [email protected]
ii. Prof. Dr. Farhan Mehmood
System and Design and Simulation Engineer,
HVDC Division , ABB, Sweden
Email: [email protected]
iii. Dr. Irfan Ahmed Khan
Assistant Prof. Department Electrical and Computer Engineering,
Texas A&M University, Texas, USA.
Email: [email protected]
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Declaration
I Hafiz Shafqat Abbas Kharal, hereby declare that I have produced the work presented in this
thesis, during the scheduled period of study. Moreover, this work has not been submitted to
obtain another degree or professional qualification.
Singed: _________________
Date: _________________
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Acknowledgements
In the Name of Allah, most Beneficent, and the most Merciful; âAs for those who say, âOur
Lord is ALLAH,â and then remain steadfast, the angels descend on them, saying: âFear ye not,
nor grieve; and rejoice in the Garden that you were promised. âWe are your friends in this life
and in the Hereafter [al-Quran]. My beloved ALLAH gave me the strength, courage, wisdom,
vision and determination to complete my PhD thesis in the age of 30 years on Higher
Education Commission (HEC) scholarship (PIN No.117-3347-EG7-061) in top one
engineering university (UET Lahore) of Pakistan. He has always bestowed his countless
blessings on me in KHARAL family.
I would like to express my sincere gratitude to my advisor Prof Dr. Muhammad Kamran for
his guidance and continuous supervision of my study and research. The achievement of this
doctoral dissertation was only possible due to his guidance and supervision. Without his
encouragement, inspirational guidance and immense knowledge I could not have finished my
work. He always extended his unconditional support and clarified my doubts and concerns:
despite of his busy schedule he was always available whenever I needed him. His guidance
helped me in all the time of research as well as the writing of this thesis and it proved as a great
opportunity for me to learn from his research expertise. I could not have found a better mentor
than him.
Besides my supervisor I also would like to thank the rest of the Departmentâs faculty especially
Prof. Dr. Muhammad Asghar Saqib, Prof. Dr. Syed Abdul Rahman Kashif for his insightful
suggestions and motivation in graduate courses and invaluable assistance during the course of
this research project.
I would like to thank Prof. Dr. A. RASHID (LATE) of the Faculty of Electrical Engineering,
COMSATS University, for providing guidance in the practical implementation of the project.
The thesis would not have come to a successful completion without the help of many students,
colleagues and friends especially Dr. Muhammad Ali, Dr. YI LI, Dr. Eishrat, Engr. Farhan
Raees, Engr. Rehmat-Ullah, Engr. Junaid Alvi, Engr. Waqas, Engr. Faisal, Engr. Shoukat
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Azeem, Engr. Mehran Tahir, Engr. Hafiz Ali Hassan and Muhammad Iqbal for sharing their
valuable ideas, stimulating discussions and assistance which they provided. They have always
offered help according to the best of their abilities whenever it was needed.
Lastly, and most importantly, I would like to thank my entire family especially my father and
late mother BEGUM MIRAJ AKBAR ROY for providing a vision and aim for higher studies
especially my elder brother Mr. Hafiz Nasir Abbas Kharal for financial supports. I owe a lot to
them as they always encouraged and helped me at every stage of both my personal and academic
life. Their blessings can never be paid off and there exists no substitute for love, prayers and
affection. In the end I would like to thank the Higher Education Commission of Pakistan for
providing funding for the implementation of this project.
Hafiz Shafqat Abbas Kharal
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Dedications
This work is dedicated to my beloved Prophet HAZRAT MUHAMMAD (PBUH)
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Abstract
The demand in the increase of efficient electrical energy has become a challenge, especially for
developing countries since their demand increase is observed with minimum planning. The
unplanned and unpredicted exponential rise in energy demand has increased the demand for
deployment of better power protection system which may withstand undue and unwanted system
failures. For this purpose, protection equipment should be installed with best efficient insulation
medium to overcome heating and quick faulty circuit isolation.
The current dissertation overviews the usage of sulfur hexafluoride (SF6) as an insulator in the
electric industry and critically compares the environmental issues associated with its nonstop use
as an insulator in high voltage (HV) appliances. Unfortunately, SF6has been identified as a very
harmful greenhouse gas by Kyoto Protocol which shows it as having 23900 times more global
warming potential (GWP) as compared to CO2 when compared over a time span of 25 years. It is
because SF6 has been included in the list of restricted gases regarding environmental protection.
Despite being nontoxic, it is heavier than air and can accumulate near the earthâs surface in case
of seepage at a facility thus replacing oxygen and causing suffocation to the workers at the
facility. These problems have gathered the attention of scientists and engineers around the world
to work on the improvement of the reliability and efficiency of the electrical power distribution
systems while taking into account that these updated technologies are safe for the environment.
This work presents the testing and development of a unique composite gaseous insulating
material using comparative evaluations among the properties of present insulating materials. The
most important objective or ambition of this thesis is to experimental investigate non-CFC
refrigerant R152a which belongs to the hydrocarbon family and has a good potential to act as an
insulating medium and to replace SF6 in electrical insulation systems because of its less GWP.In
this thesis theoretical as well as experimental performance of R152a have been discussed and
explicitly correlated saturated and superheated properties in comparison with existing insulating
materials.
R152a gas demonstrates good dielectric properties with low-temperature usage possibilities
under liquefaction conditions and environmental effects. The experimental study of power
frequency breakdown characteristics of R152a/CO2 has been analyzed under different pressure
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(0.2Mpa-0.6Mpa) and mixing ratios (50/50, 60/40, 70/30, 80/20, and 90/10%) conditions and
gap differences (6mm-18mm). GWP and PD characteristics have also been examined for the
proposed gas mixtureâs insulation performance. The results indicate that the breakdown voltages
of R152a/CO2 gas mixture demonstrate a saturated trend in growth with varied gas pressure,
mixing ratios, and gap differences. The insulation performance of the gas mixture with 80/20%
R152a/CO2 can reach more than 96% of pure SF6.The development of this proposed composite
insulating material will result in superior insulating properties, reduced cost, and supplementary
ecological traits. Overall, this work will bring a potential cost-effective and environment-friendly
gaseous insulator for utility companies and power equipment manufacturers.
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Table of Content
DeclarationâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...âŠ.............. Iii
Acknowledgements âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ....... viv
Dedications âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.................................... vi
AbstractâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. vi
Table of Contents âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. ix
List of Figures âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... xiii
List of Tables âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. xv
List of Abbreviations âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. xvi
1 Chapter 1 Introduction âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 1
1.0 Introduction âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 1
1.1 Background âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 2
1.2 Disadvantages of SF6âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.................................................. 4
1.2.1 Disadvantages of SF6 Equipment âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...âŠ... 4
1.3 Aim of this Work âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 6
1.3.1 Contributions to new research to achieve aim âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ.. 6
1.4 Outline of the Thesis âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 6
2 Chapter 2 Literature Review âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 8
2.0 Theory and Literature Review of SF6 equipment âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 8
2.1 Vital SF6 Gas theory âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 8
2.2 Properties of SF6 Gas âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 8
2.3 Electrical Performance of SF6 Gas âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 10
2.4 The Usage of SF6 in Circuit Breakers (CB)âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 12
2.5 Benefits of SF6 Switchgear in Comparison to Oil or Air âŠâŠâŠâŠâŠâŠâŠ............. 13
2.6 SF6 circuit breakers advantages âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 14
2.7 The Usage of SF6 in Gas Insulated Substations (GIS)âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 14
2.8 Target Design of Bus bar for Future StudiesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 16
2.9 ConclusionâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.........âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 16
2.9.1 SF6 Properties and Study Model of Gas Insulated EquipmentâŠâŠ.âŠâŠâŠâŠâŠâŠ 16
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3 Chapter 3 Merits and Demerits of SF6 Verses Alternative Gases for Future
AspectsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.
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3.0 Analysis on Merit and Demerits of SF6 Verses Alternative Gases for Future
Aspects Characterization of Isolated CompoundsâŠâŠâŠ.âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.
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3.1 Merits of SF6 GasâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 17
3.1.1 Complications associated with the continuous usage of SF6âŠâŠâŠâŠâŠâŠâŠâŠâŠ 18
3.2 Ideal properties of alternate insulation mediumâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 18
3.3 Gaseous replacement for SF6 as insulation mediumâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 19
3.3.1 Electronegative gasesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 19
3.3.2 Charge transportation and conduction in gasesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 20
3.3.3 Townsend's PrincipleâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...âŠâŠ. 20
3.3.4 Equation designed for growth CurrentâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 21
3.3.5 Townsend's criterion for breakdownâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 22
3.4 Review of SF6 alternativesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 22
3.4.1 Mixtures with SF6âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 22
3.4.2 Different Alternatives of SF6âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 23
3.5 R152aCharacteristicsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...âŠ. 24
3.5.1 Physicalproperties of R152aâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 25
3.6 Environmental features of SF6, R152a and Gas mixtures âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 27
3.6.1 Global Warming Potential (GWP)âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 27
3.6.2 Atmospheric lifetime âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 27
3.6.3 Ozone depletion potential âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 28
3.6.4 A Comparison of the dielectric strengths of SF6 with Alternative gasesâŠâŠâŠâŠ.. 28
3.7 Conclusion of Gaseous Replacement for SF6âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 28
4 Chapter 4 Leakage of SF6 Gas from Power PlantsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 30
4.0 Introduction âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠâŠ 30
4.1 SF6 equipment review âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 30
4.2 Utilization of SF6 equipment in the distribution networkâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 32
4.3 Worldwide SF6 usage and its effectâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 33
4.4 ConclusionâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 37
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5 Chapter 5 Development Test, Laboratory and Investigational Methodology... 39
5.0 IntroductionâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 39
5.1 Laboratory Setup and Assembly of Test ElectrodesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠ 39
5.2 Insulating Materials Breakdown VoltageâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.⊠41
5.3 Gases Breakdown VoltageâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 42
5.3.1 HVAC Test Arrangement for Breakdown VoltageâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 44
5.3.2 HVAC Arrangement for Breakdown VoltageâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 45
5.4 HVDC TestâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 46
5.4.1 HVDC Arrangement for Breakdown VoltageâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 46
5.5 List of Equipmentâs used in experimental testsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 47
5.5.1 Control DeskâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠâŠâŠâŠ 47
5.5.2 Pressure/ Vacuum Vessel (HV 9134) âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 48
5.5.3 ApplicationsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 48
5.5.4 Test Transformer (HV 9105) âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 49
5.5.5 ApplicationâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 49
5.5.6 Peak Voltmeter (HV 9150) for Digital DisplayâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 49
5.5.7 ApplicationsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 50
5.5.8 Discharge Rod (HV 9107) âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 50
5.5.9 ApplicationâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 50
5.5.10 Aluminum (HV 9108) Rod ConnectingâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 50
5.5.11 ApplicationâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 51
5.5.12 Aluminum (HV 9109) Cup ConnectingâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 51
5.5.13 ApplicationsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 51
6 Chapter Experimental Results of R152+ CO2 Mixtures: as a Potential
Alternative to SF6 6 âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.
52
6.0 IntroductionâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 52
6.1 Power Frequency Breakdown Voltage Experiments and ResultsâŠâŠâŠâŠâŠâŠâŠ. 52
6.1.1 Experimental ProcedureâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 52
6.1.2 Gas Mixture ProcedureâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 52
6.2 Calculation of Accurate Gas Mixture PressureâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 53
6.3 Mixture Ratio AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 54
xii
6.3.1 Dielectric Strength AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.⊠55
6.4 Gap Difference AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 55
6.5 Statistical Analysis of R152aâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 56
6.6 Global Warming Potential (GWP) AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...âŠâŠ.. 57
6.7 Synergistic effectâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 57
6.7.1 Synergistic effect of R152 /COâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 58
6.8 Insulation Self-Recoverability test of Gas mixturesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 58
6.9 R152a/CO2 Liquefaction Temperature AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 59
7 Chapter 7 Conclusion and Future DirectionsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 63
7.0 ConclusionâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 63
7.2 Future workâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 64
References âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 66
Appendix AâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 77
A1 Different alternative of SF6 gas. âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 77
A2 Characteristics of References SF6 Verses R152aâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 77
A3 Association of SF6 replacementâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 78
Appendix BâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 79
Appendix CâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...... 81
C1 Laboratory Test Setup and Assembly of Test ElectrodesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 81
Appendix DâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...... 83
D1 Calculation of Accurate Gas Mixture PressureâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 83
D2 Gap Difference AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 83
D3 Global Warming Potential (GWP) AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 84
D4 Synergistic effectâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 84
D5 R152a/CO2 Liquefaction Temperature AnalysisâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 84
Appendix E âŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠâŠâŠâŠâŠ.................................................... 85
E1 Research papers published on this projectâŠâŠâŠâŠâŠâŠâŠâŠ.âŠâŠâŠâŠâŠâŠ.. 85
xiii
List of Figures
Figure 1.1 The development of the global mean atmospheric content of SF6. The linear
fit shows an annual growth of 0.26pptâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ..
2
Figure 2.1 Octahedral molecular geometry of SF6 moleculeâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 8
Figure 2.2 Comparisons of SF6, Air, vacuum and Oil for dielectric strength (DS)âŠâŠ... 10
Figure 2.3 Negative (-) lightning impulses, negative (-) switching impulses, N2:SF6 AC
breakdown voltages of these gaseous mixtures at 60 HzâŠâŠâŠâŠâŠâŠâŠâŠ..
11
Figure 2.4 SF6 and air interruption capabilityâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 11
Figure 2.5 Puffer along with rotating arc CB types in enhanced qualityâŠâŠâŠâŠâŠâŠâŠ 12
Figure 2.6 SF6 deionization time constants in contrast with other gasesâŠâŠâŠâŠâŠâŠ... 13
Figure 2.7 From left Oil, in middle air blast and in right SF6 circuit breakerâŠâŠâŠâŠâŠ 14
Figure 2.8 Sectional view of (420 kV) GIS of a cove among double bus-bar systemâŠâŠ 15
Figure 3.1 Manufacture compliances with impact of SF6 regulationâŠâŠâŠâŠâŠâŠâŠ..... 18
Figure 3.2 Elements with its electronegativityâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 20
Figure 3.3 Mechanism for Townsend dischargeâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.⊠21
Figure 3.4 SF6/N2 mixtures with different pressureâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 23
Figure 3.5 Electronegativity of elementsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 25
Figure 4.1 Insulation medium and its voltage rangesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 30
Figure 4.2 Medium voltage circuit breaker usageâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 31
Figure 4.3 Dielectric strength dependency on inter-electrode distanceâŠâŠâŠâŠâŠâŠâŠ.. 31
Figure 4.4 Classical distribution networkâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 32
Figure 4.5 SF6 usage in distribution networkâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.⊠33
Figure 4.6 Percentage wise use of GIL, GIS and CBâsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 36
Figure 4.7 Estimated 25-year leakage of SF6 worldwide distribution equipmentâŠâŠâŠ.. 37
Figure 5.1 Experimental set up to examine R152a/CO2 breakdown voltage by sphere-
sphere electrodesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ...
40
Figure 5.2 Test equipment used: (a) Control and measurement unit(b) Testing vessel
(HV-9134) (c) Experimental setup for DC (d) Spark formation comparisonâŠ
40
Figure 5.3 Discharge (breakdown) development in a gas volume between two
xiv
electrodes by electron avalanche processâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 43
Figure 5.4 Schematic diagram for AC testâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 45
Figure 5.5 AC Experimental SetupâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 45
Figure 5.6 HVDC test represents in schematic diagramâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 46
Figure 5.7 DC experimental setupâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 47
Figure 5.8 Vacuum/pressure vesselâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 48
Figure 5.9 Test transformerâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 49
Figure 5.10 Peak voltmeter (PV)âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 50
Figure 5.11 Discharge rodâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 50
Figure 5.12 Connecting rodâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 50
Figure 5.13 Connecting aluminum cupâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 51
Figure 6.1 Power frequency breakdown voltage of R152a/CO2 gas at varying mixture
ratio and8 mm electrode gap distanceâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.
54
Figure 6.2 Breakdown characteristic comparison of R152a/CO2 gas at 80%/20%
mixture ratio and SF6 at 8 mm electrode gap distanceâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ.
55
Figure 6.3 Breakdown voltages of R152a/CO2 gas varying the gap distance (4â16 mm)
at different mixture ratioâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ
56
Figure 6.4 GWP analysis of R152a/CO2 gas mixtureâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 57
Figure 6.5 Insulation self-recoverabilityâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 59
Figure 6.6 Saturated vapor pressure R152a and SF6âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 60
Figure 6.7 Liquefaction temperature of pure gasesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 60
Figure 6.8 Liquefaction temperatures of R152aat different pressure and mixture ratioâŠ. 61
Figure 6.9 Simulation of (a) breakdown voltage, (b) electric filed under different
mixturesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.
62
Figure 6.10 Carbon fumes deposited on electrodesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.. 62
xv
List of Table
Table 2.1 Summing up the vital distinctiveness of (SF6) gasâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 9
Table 3.1 Comparison of SF6 with different alternativesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 24
Table 3.2 Different properties of R152aâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 25
Table 3.3 Contrast between physical along with chemical properties of R152a vs SF6âŠâŠ. 26
Table 3.4 GWP of different gasesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 26
Table 3.5 Atmospheric lifetime of different gasesâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 27
Table 4.1 Several devices and their functionâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 34
Table 4.2 Worldwide usage and leakage of SF6 from all RMUâsâŠâŠâŠâŠâŠâŠâŠâŠâŠ... 35
Table 4.3 Worldwide SF6 usage and leakages from every CBâsâŠâŠâŠâŠâŠâŠâŠâŠâŠ.⊠35
Table 4.4 Worldwide usage and leakage of SF6 from all switchesâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 35
Table 4.5 Total amount of SF6 use in all RMUâs, CBâs and switchesâŠâŠâŠâŠâŠâŠâŠâŠ 36
Table 4.6 Worldwide usage and leakage of SF6 from all GISâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 36
Table 4.7 Estimated 25-year leakage of SF6 worldwide distribution equipmentâŠâŠâŠâŠ 37
Table 5.1 Test setup specificationâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 41
Table 5.2 Descriptions of control deskâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 47
Table 6.1 Experimental constraintsâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 52
Table 6.2 Different mixture ratio of R152a and CO2âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ.âŠ. 53
Table 6.3 Statistical analysis of R152aâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ 56
Table 6.4 Synergistic effect of R152a/CO2âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ. 58
xvi
List of Abbreviations
AC Alternating Current
R-152a Difluoroethane
CO2 Carbon Di-oxide
SF6 Sulphur Hexafluoride
N2 Nitrogen
GIL Gas Insulated Line
GIS Gas Insulated Switchgear
GWP Global Warming Potential
IP Ion Pair
ODP Ozone Depletion Potential
PFC Perfluorocarbon
VFT Very Fast Transient Circuit breaker
LV Low Voltage (220 V to 1 kV)
MV Medium Voltage (1 kV to 52 kV)
HV High Voltage (52 kV to 300 kV)
EHV Extra High Voltage (300 kV to 800 kV)
GWP Global Warming Potential
ODP Ozone Depleting Potential
IR Infrared
PPTV Parts Per Trillion per Volume
EN Electronegativity
EA Electron Affinity
Î Ionization Coefficient
(đž/đ)đđđđ Critical reduced electric field strength
αeff(E) Effective Ionization Function
xvii
PD Partial DISCHARGE
PDIV Partial discharge inception voltage
BDV Breakdown voltage
BIL Basic impulse level
LI Lighting impulse
U50 Voltage at which there is a 50 percent probability of a break down
occurring
Up Rated lightning impulse withstand voltage
MPa Mega Pascal (unit of pressure)
T Townsend (unit)
Bar Gorbar bar gauge (unit of pressure)
GC-MS Gas chromatography and mass spectroscopy detector
NOP Normally open point
EHC Extra high current
BS British standard
MW Molecular Weight
I Current carried by conductor
Ich Chopping current
K0 Gas constant of the filled gas in GIS
K Particle length
L Inductance
M Mass of the particle
P Pressure
1
Chapter 01
Introduction
1.0 Introduction
Power system network comprises of generation, transmission and distribution. It uses energy
provided by water, coal, diesel etc. and converts it to electrical energy which is then transmitted by
the transmission network; finally, distribution network distributes the energy to domestic and
industrial customers. For power system to be efficient, losses should be minimized and equipment
with high insulation properties should be used to avoid any major mishap or failure of equipment.
Different insulation medium have been used over past three decades, for example, oil has been used
in oil bulk circuit breakers and it is still being used for cooling and insulation purposes in power and
auto-transformer, while air blast, air break and vacuum circuit breakers have also been used but due
to poor insulation properties and high maintenance cost the switchgear insulation medium is
preferred to be sulphur-hexaflouride (SF6) gas which is one of the most utilized insulation material
in switch gear throughout the world and power system grids are shifting from Air insulated sub-
stations (AIS) to gas insulated sub-stations (GIS). GIS system is now extensively used in
distribution transmission networks as an insulating medium in a large range of gas insulated
switchgear (GIS) for switching, earth switching, circuit breaking and general circuit protection. This
chapter will highlight the literature review, components of the conceptual model of the thesis and
summarize the outline that comprises an indication of the major achievements.
The worlds stipulate on electric power are growing. At the same time, conventional power
production by burning fossil fuels must be condensed to lessen the harmful effects on the
environment due to the emission of CO2 from burning coal and gas in power generation plants. In
addition, nuclear power has been phased out by force in some countries [1-2]. Energy demands are
being covered by renewable energy sources including wind and solar power. For example, in
Europe, the coasts of Atlantic and the North Sea have got lots of wind turbines to generate
electricity. Solar power is being utilized at its best in southern countries or Sahara-desert [3]. This
also needs a significant upgrade of the power grid to bring the generated electricity to remote load
centers which are mostly far from the production sites. So, with the rapid increase in demand of
electricity the system also required to be shifted to UHV system which in return requires greater
insulation of higher rated equipment so save the equipment from over-voltages surges. Keeping in
the view of current insulation requirement for grid station equipment Sulfur hexafluoride (SF6) is a
potential insulator and arc-quenching medium, which is being extensively used in electric power
2
system devices due to eminent properties like high dielectric strength (DS), physical stable and
electrically superior from others [3-5]. However, environmental apprehension has been raised
subsequent to using gas in huge quantities in various high voltage (HV) sub-stations as well as
industries. Global warming is affected by this apprehension. Consequently, SF6 is very effective
infrared absorber and greenhouse gas. The linear fit shows an annual growth of 0.26ppt as shown in
Fig. 1.1 [6].
1.1 Background
Moissan and Lebeau were responsible to synthesize and portray in (1900), alsosulphur hexafluoride
(SF6) for the first time described; the gas applications in large number were quite sophisticated
around 1940, further more in 1947, it developed available in commercial form [7]. This issue of the
usage of SF6 in many applications or electrical industries have been summarized and reviewed by
Brunt, Christophoro and Olthoff, with a conclusion of its extensive use in commercial and industrial
research [8]. Apart from the usage of SF6 by the electrical and electronic industries, it is also used in
the processing of semiconductors, refining of magnesium, as insulating gas for thermal and sonic
applications, airplane tires, air-sole shoes, leaks checking, etc.
Figure 1.1.The development of the global mean atmospheric content of SF6. The linear fit shows an annual
growth of 0.26 ppt [6].
In the eighth decade of twentieth century, medium-voltage circuit breakers mainly relied on oil or
air as their major insulating mediums [9]. With the passage of time, air and oil were replaced by SF6
and vacuum as insulating media [10]. These changes allowed the use of a higher range of voltage in
a smaller space with the provision of a relatively maintenance and hazard free system of SF6as
compared to the usage of oil [11-13]. The other main reason for the large-scale development of SF6
and vacuum was the design of many smaller-sized substations than the ones made by air or oil as
3
insulating media [14]. This is due to the requirement of a very small gap between the electrodes to
break a circuit while using SF6 or vacuum as compared to any other technology. This has an overall
effect of designing very small sized equipment for electric industry which in turn makes the
industry cost-effective also. The old vacuum technology as interrupting dielectric did quite well up
to high voltages of 132kV[15-16] but now this technology has been seized due to a better
alternative, i.e. SF6 which proved effective in its use in equipment up to 800 kV [16]. This has
resulted in SF6 being an exclusive candidate for high voltage (52-300 kV) and extra high voltage
(300-800 kV) networks without a suitable alternate as an insulating material with similar insulation
and interruption performance [17]. The following properties of SF6 can better describe the reasons
of its popularity and wide use as a dielectric media.
Chemical inertness [18]
Low boiling point [14]
Thermal stability up to 500ËC temperatures [3,15]
Strong electro negativity and excellent arc extinction properties [3,16]
Non-toxicity [3]
Non-flammability [19]
Three times stronger than air in terms of breakdown voltage [18]
Very quick arc extinction recovery time [3]
Kindness to stratosphere and almost zero percent harm to ozone in that region [20]
The above-mentioned characteristics of SF6 are responsible for the development of equipment
having the following properties:
Smaller sizes because of little gaps among electrodes because of the high breakdown voltage
of SF6 [20]
Small-sized substations because of smaller switchgear dimensions [21]
A high-level insulation as well as circuit breaking performance [22]
A proven safety demonstration [23]
Comparatively low insulating medium cost because of large scale production and increasing
demand [24]
Almost maintenance free SF6vessels
4
All the above advantages render it the best candidate for the power distribution network.
1.2 Disadvantages of SF6
The hazards to the environment associated with the continuous use of SF6 in insulation industry are:
The indoor electrical transformers which are fire-resistant and have SF6 as insulation
medium are used to protect the indoor circuits from fire [25]. The major problem with its
wide use is that it has a high global warming potential (GWP) which has been responsible
for its declaration as a restricted greenhouse-gas by Kyoto protocol [3,25]
SF6 is heavier in comparison to normal air which gathers it at the lower regions of the
substation at the points of cable trenches, thus replacing the air in these regions. It is a
potential hazard for the people working in these places due to oxygen deficiency
SF6 can decompose at an elevated temperature (above about 500ËC) [26]. On occurrence of
arcing while a circuit breaker switching, the decomposition products can cause skin-damage
or eye irritation
Due to SF6 being a good absorber of infrared radiation [8], its GWP is about 23000 times
greater than that of CO2 [27].
The worst thing is that it stays very long in earthâs atmosphere due to being inert and
cannot be removed readily [28].
1.2.1 Disadvantages of SF6equipment
The installation cost is a disadvantage because of the high cost of GIS installation compared
to AIS [29]
Due to high stability and inertness of SF6, it is usually maintenance free but if maintenance
is required, it requires skilled personnel which are hard to find
Due to being present at the critical nodes on the power grid, GIS installations can cost a lot
of revenue in case of failure as their faults are difficult and expensive to trace out and repair.
So, they may cause longer power outages in these circumstances. Customers usually donât
like longer power outages which can be a concern while using SF6 in this equipment
Various potential deficiencies are found in SF6 containing systems which results in
progressive corrosion of insulation quality and may perhaps cause to failure. The issue is
5
that it is almost impossible to rectify the problem with old methods due to the closed nature
of the system
Till date, there are not many proposed solutions to replace SF6 as a foremost insulator in extra high
voltage (EHV), high voltage (HV) moreover medium voltage (MV) networks. There is a suggestion
to use vacuum technology but there is no evidence in literature that could allow full replacement of
SF6. So far, the best solution to replace SF6 is to use it mixed with other gas which reduces SF6
quantitatively but its demerit is that it reduces the efficiency of insulating the equipment by
quenching the arc. There are different combinations of SF6 reported including SF6+CF4, SF6+Air,
SF6+N2 and also SF6+CO2 gases mixtures, out of which SF6+N2 are the best among these
combinations and it has been adopted in GIS and GIL manufacture [3,30,31]. In this case, the
performance is not altered a lot due to N2 being an inert gas and it allows the usage of SF6 on lower
temperatures as well [31]. The search for SF6 alternatives has already been in progress for decades.
Current research is aimed at finding an alternative which is not necessarily better than SF6 but
having similar insulation capacity and less harmful to the environment. The main research objective
and aim of current thesis is the search of an alternative for the use of SF6 in distribution network
that may effectively be used as a replacement of SF6 in near future. The suggested alternative is not
expected to have same effectiveness as SF6 but should have less environmental issues still keeping
in mind the cost effectiveness.
A good SF6 gas alternative should possess the following physical, chemical, and environmental properties.
It should have very high electric strength
It must quench the arc very well and after that recover fast to be ready for next quench
It should have low boiling point
It should be compatible with existing switchgear materials
Its handling must be easy. Its toxicity should be very low with no dangerous decomposition
products
Its global warming and ozone depletion potentials must be very low
It should be least damaging to the environment
6
1.3 Aim of the Work
The aim of this study includes existing literature review of different combinations of gases which
has been used as insulation medium of high voltage switch gear and to compare their performance
with SF6 gas in terms of insulation quality and to evaluate on which scale they damage the ozone
layer, the study also carries out theoretical assessment of various SF6 elimination options and
experimental testing. This study also discusses other viable substitutes available to SF6 gas and
while also justifying why other options are referred. Finally, this thesis will review the performance
of R152a/CO2 gas mixture and draw comparative analysis with SF6 gas.
1.3.1 Contributions to achieve aim
Following are the steps carried out to achieve the above stated goals:
Theoretical evaluation of various SF6 gas elimination options along with various
measurements and simulations has been carried out
Traditionally new R-152a insulation gases along with its variants are evaluated by
comprehensive analysis of the physical and chemical properties of R-152a and R-
152+CO2 gas mixtures with classical breakdown experiments
Experimental investigation of this R-152a gas along with its applications as insulation
medium on medium voltage switches has been carried out
Comparison of the insulating properties of R-152a gas and its variants with SF6 has been
carried out through experimentation
The predicted breakdown voltages for the novel gas R-152a and a set of other known
gases have been validated.
The probability of over voltages when vacuum or different gases installed is studied by
statistical methods
Proposal about using a vacuum switch gear to employ this R-152+CO2 novel gas mixture as
replacement insulation to SF6 gas.
1.4 Outline of the Thesis
1.4.1 Chapter 2
Chapter 2 elaborates the characteristics of SF6 gas along with literature review, properties of SF6 in
details. A brief overview of current published papers regarding different insulation medium has
been discussed.
7
1.4.2 Chapter 3
Chapter 3 includes the characterization of the widely used SF6 gas in insulation industry and its
environmental threat with regard to Pakistan and the globe. The discussion also includes those
important aspects and reasons which limit the use of SF6. It also enlists the alternatives of SF6 gas
that have been previously suggested. The other main point of this chapter is to present a clear and
concrete picture of the published literature about the characteristics of R152a gas and its other
different mixture variants which play some sort of role in this industry.
1.4.3 Chapter 4
In Chapter-4 includes a review of the SF6 usage in power plants and gas leakage. It includesits
effects on the environment as well.
1.4.4 Chapter 5
Chapter 5 encompasses the discussion on the equipment used in the laboratory and the procedures
and techniques employed throughout the present study. Preliminary tests used to establish the
decisive testing on the apparatus and the gas mixtures.
1.4.5 Chapter 6
This chapter presents experimental and simulated results which enlist the comparative study on SF6
and R-152a+CO2 gas mixture. It also includes the results of the simulations performed using
different software. Finally, the development of a proposed composite insulating material with
superior insulating properties reduced cost, and supplementary ecological traits.
1.4.6 Chapter 7
Chapter 7 is the conclusive chapter of this thesis. It concludes the research carried out for this thesis
and briefly enlists the possible future studies.
8
Chapter 02
Literature Review
2.0 Theory and Literature Review of SF6 Equipment
Gas insulation while making power equipment, especially for designing HV equipment utilizes SF6
widely. This is because of the better electrical performance along with the stability of SF6. This
section consequently analyzes the properties of SF6& its evolution in electronics as well as
electrical power industries.
2.1 Vital SF6 Gas Theory
Moissan and Lebeau were the founders of the SF6 synthesis in the year 1900 [32]. Four decades
after its first synthesis, SF6 was reported as having insulation properties and a good candidate for
the insulation equipment compared to fluorocarbons and the oil used in the transformers [33-35].
SF6 was used as a quenching medium for the first time in 1950 in circuit breakers [36]. After three
decades, there was interest among scientists to find out its breakdown and partial discharge
mechanisms [36-37].
2.2 Properties of SF6 Gas
SF6 molecule comprises of six fluorines attached to the sulphur atom. In these situations, where F
atoms lie in an octahedral manner (Fig.2.1) i.e. four in a square plane around the central atom and
two above and below. Each and every one has its bond angles either 90 degree or 180 degrees [38].
Figure 2.1. Octahedral molecular geometry of SF6 molecule [38]
Due to its strong electronegative behavior, SF6 can attract free electrons generated during the arcing
of electric current. As a result, it gets converted to anions which are heavier than the free electrons.
Thus, greater voltage is required to breakdown these fewer mobile anions and breakdown the gas.
9
The following section [40] gives a portrayal of the compensation of any gas which one is
electronegative.
âSF6 is an electronegative halogen gas having good dielectric properties. Particles of an
electronegative gas have an affinity to attach themselves to free electrons producing less mobile and
heavy negative ions. The contribution of the latter to the ionization process creating electron
avalanches is much less as compared to an electron. Hence, the electric field stress required to cause
breakdown of an electronegative gas is highâ.
SF6 forms as an exothermic reaction between the molecular sulphur and fluorine as described in
equation 2.1. Due to its high stability, it is very difficult to breakdownSF6 into its components, even
at higher temperatures. That is why it can easily be used in electrical equipment mainly as a
insulating materials at temperatures of up to 200âŠC [41].
S2 + 6F2 â 2SF6 + 524 kcal (2.1)
SF6 has excellent heat transfer properties, as well as the additional vital features of these potential
gases as specified in (Table 2.1).
Table 2.1. Summing up the vital distinctiveness of (SF6)gas [37][41][45]
(SF6-Properties) (Statistics)
0.1Mpa Relative -Density 6.256 kg -per-m3
0.1MPa at (0°C) Thermal Conductivity 0.0212-Wm-1K-1
0.1Mpa Boiling point â64°Cor (209 K)
Water Solubility Soluble inSlightly
Liquefied Pressure (21°C) 2.1-MPa
GWP (Global Warming Potential) 24,000
SF6 gas Toxicity None
SF6 with extra concentrations will lead to suffocation
At high pressure and room temperature SF6will be able to store. Its boiling point (â64âŠC at 0.1Mpa)
is relatively low. In general, SF6 can be used in insulated equipment with (0.30-0.60Mpa) pressures.
SF6 is three times heavier than air, as a result it stays on ground level and even though its behavior
is non-toxic, a high density SF6 with extra concentrations will lead to suffocation [3]. During
electrical discharge, its products that are generated such as S2F10 and SOF2 are highly toxic and
10
corrosive compounds. Till date there are no issues reported with SF6 handling, availability and
reliable availability. From sixth decade of nineteenth century till the ninth decade, its price was
reasonably constant, but now that price has increased about ten times (about $30/lb.) [42]. All the
pros discussed in the previous paragraphs render SF6 as an excellent arc insulator. Therefore,
substations are equipped with SF6 gas. Transformers use SF6 as insulating or cooling medium and
switchgears use it for quenching the arc in HV & MV applications.
2.3 Electrical Performance of SF6
SF6 has a dielectric withstand property which is two times superior to air at normal pressure (Fig.
2.2). Upon its use at higher pressures (3-5 atm), the dielectric performance becomes ten times
superior to air. These types of potential gases capture free moving electrons, since negative (-) ions
consequently strike the formation in form of electrical discharges. The admirable dielectric strength
(DS) of SF6 is major reason for its usage in (GIS) gas insulated substations. Pedersen and Cookson
[42-43] have given information about characteristics of SF6 gas with different mixing ratios. The
measurement was applied to the coaxial cylinder at (89 mm/226 mm) electrode geometries with
negative (-) switching impulse, lightning impulse and discontinuous voltage. Fig. 2.3 refers to the
breakdown voltage withstand ability of SF6+N2 gases mixture at pressure about 0.45 MPa of these
gases. The lack of strength is due to surface roughness, dissimilar conductor materials & spacer
structures design in practical manufactures work.
Fig.2.2. Comparisons of SF6, Air, vacuum and Oil for Dielectric strength (DS) [44].
Several gases mixtures with a reduced volume of SF6, such as 80%/20%SF6: N2 present weaker
dielectric strength (DS) rather than a pure SF6 [45]. For example, in case of switching, these new
11
solutions of mixed gases have approximately 5% lower dielectric strength (DS). Moreover, the
dielectric strength (DS) in AC is condensed &is not greater than 3.5%, in contrast of unpolluted
SF6.
Figure 2.3. Negative (-) lightning impulses, negative (-) switching impulses, N2:SF6 AC breakdown voltages
of these gaseous mixtures at 60Hz [45-46].
SF6 has capability to interrupt current (Fig. 2.4). SF6 efficiently controls several circuit breakers
because ithas electronegative features & properties as discussed previously, due to its superb
cooling potential at very high temperatures (1200â4500âŠC) where the extinguishing of arcs occurs.
The phenomenon is that the gas takes up the energy of the arc to dissociate, thus providing the
cooling effect. The graph below shows the results of investigations from 1953 and explains that SF6
has better interruption capability than the air [42]-[46].
Figure 2.4. SF6 and air Interruption capability [46].
12
2.4 The Usage of SF6 in Circuit Breakers (CB)
The available SF6 circuit breakers are of two types, the first one called as the âpuffer typeâ and the
second one as ârotating arc typeâ. The first one resembles to the old air blast type system while in
the second, the arc moves with the help of magnetic fields. Here, only the âpuffer typeâ has been
discussed as the other one is only used in distribution voltages shown in (fig. 2.5) [47].
A puffer type circuit breaker is characterized by the SF6 flow over the arc coming out of the circuit
breaker contacts. The heating effect of the arc is responsible for the movement of the gas. Large
currents produce enough heat to start the flow of the gas while for smaller currents; the heating
effect is insufficient so it is desirable to utilize a pre-compressed quantity of SF6.When a circuit
breaker is opened, its main parts separate followed by the arc contacts. Thus, by the volume getting
decreased, the pressure of SF6 is increased.
Figure 2.5. Puffer along with rotating arc CB types in enhanced quality [47]
This keeps happening till the contacts continue to separate apart and eventually an arc is drawn
which force the gases to move axially with the arc, which eventually causes the extinction of the
arc. For the larger currents, the breaker opening is slowed because of the gas pressure inside the
piston. Contrary to that, for low current values, the arc diameter is minute and the flow of gas
happens automatically without being stopped.SF6 Circuit breakers, due to its enormously stumpy
deionization time constant, in contrast with air is shown in (Fig. 2.6).
13
It has critical parameter like time constant which partially depicts circuit interrupting abilities with
efficient circuit breakers (CB). This SF6 gas time constant is enormously dumpy due to its
electronegative properties and nature: as a result, it is capable to withstand extinction of the arc.
Figure 2.6. SF6deionization time constants in contrast with other gases [47].
Although SF6 gas is quite stable, but in interrupting the arcs and electric discharges, it might
decompose slightly, giving rise to decomposition products. Usually absorbers are used to keep the
amounts of the gaseous products low because of their poisonous nature. That is why specialized
personnel are required to open the damaged SF6 filled appliances for maintenance. The
decomposition products may be metallic fluorides which can decompose quickly after opening and
not harmful to the environment.
2.5 Benefits of SF6 Switchgear in Comparison to Oil or Air
The use of oil for insulation purpose is preferable over SF6 and air, but there are certain limitations
to the use of oil. If the oil gets very little number of contaminants like water or carbon, its
performance dies briskly. As per manufacturer manual âfresh oil can normally be expected to have
a dielectric strength of around 70 kV when it is placed between two 20 mm spheres, 2.5 mm apartâ
[49-50]. The dielectric strength of the used oil is generally over 15 kV. During the arcing process,
the hydrogen gas around the arc plays an important role, thus making the oil a very good insulating
material.
Air circuit breakers are worn out and are functional at 12 kV. Thus, they have the disadvantage that
they cannot be used for extra high voltages. Oil circuit breakers can be used up to 72 kV. As the
moisture in oil has a detrimental effect on dielectric strength [51] of circuit breaker, thus they
require repetitive maintenance. Also, oil circuit breakers face fire hazards problems. Air Blast and
Magnetic Air circuit-breakers are massive and inconvenient. Vacuum circuit breakers (VCBs) are
environment friendly and are engaged in medium voltage levels (5-38 kV) [52]. Their construction
14
is simple and lesser number of components is used. They are maintenance free. Substationâs size is
reduced when VCBs are used instead of oil and air circuit breakers. Use of VCBs is limited due to
their high cost, non-uniformity of dielectric strength. VCBs cannot be used for extra high voltage
(EHV) and ultrahigh voltage systems (UHV) [53].In (fig.2.7) from Oil, Air Blast and SF6 circuit
breakers are presented. For medium voltage (MV) range, VCBs are used, but for high voltage
systems (HV) sulfur hexafluoride (SF6) is used. From the early 1960s, SF6 is used. SF6 circuit
breakers are mostly used in EHV and UHV applications because of their numerous benefits such as
superior performance, prolonged contact life and simple construction.
Fig 2.7. From left Oil, in middle Air Blast and in right SF6 circuitbreaker [50].
2.6 SF6 circuit breakers advantages
Good properties of SF6 result in various applications with added benefits:
High breakdown voltage of SF6results in smaller electrode clearance [3,52]
Smaller switchgear dimensionâs result in smaller substation sizes [8]
Higher insulation and circuit breaking [54]
Non-toxic (non-flammable), also non-explosive environment results in good operations.
SF6 results in reduced equipment cost [14]
Reduced maintenance is required for SF6 based systems [55]
2.7 The UsageofSF6in Gas Insulated Substations (GIS)
Typically, SF6 is used primarily as an insulator for devices used within gas insulated substations. A
420kV pattern of Gas Insulated Substations configuration clearly revealed in (Fig. 2.8).
15
Fig 2.8. Sectional view of (420kV) GIS of a cove among double bus-bar system [56].
The Design or construction of bus-bar system either three phase orsingle-phase
enclosures; it has following parameters (a) conductors (b) supporting spacers (c)
cylindrical enclosures also. In bus-bar dimensions are cautiously chosen according to the
required electrical impulse as well as the power that the switching impulse faces. In
addition, numerous other vital factors must be well thought-out to make its dimensions
reasonable. The list is given blow:
Evaluation of the electrical stresses and its effects belonging to many types
Dimensioning of GIS systems as well as components
Consideration for Insulation interfaces (solid plus gaseous plus liquid insulation
congregate)
Thermal details
Every power appliance bears continuous stress due to the operating voltage and from time to time
essentially endures certain level of voltage in excess of specified value in which system voltages are
operating, such as (a) lightning impulse voltage [BIL] or (b) switching impulse voltage. Lightning
impulse voltage occurs as a result of a usual and natural phenomenon, the stander of wave shape
(1.2/50) of electric lightening impulse [57â58] with a period of front / tail. Circuit breakers
connecting and disconnecting produced the switching impulse voltages itself from the system. A
good quality design substation must withstand every type of voltages tress. It will make sure the
failure of dielectric never takes place. More and more protective devices such as surge arresters and
switches are frequently installed in substations to reduce the over-voltage levels.
16
The dimensions of the intact bus bar assemblies are essentially dig out with efficient insulating
medium properties. This one totally delays one operation voltage and further conditions likesâ its
surface circumstance of any conductor if it is rough, can root locally eminent electrical fields.
In short, substation construction along with design depends on many factors. To develop a steadfast
insulation system or suitable dimension for any substations, imperative factors must be kept in
mind, particularly thermal stability. Protective devices can be used to manage voltage magnitude in
combination with an insulation system. In Chapter 3, the aspects of thermal plus insulation design
are briefly explained with an assessment of dissimilar types of numerous dielectric materials.
2.8 Target Design of Bus-bar for Future Studies
A base plan of the gas insulated bus-bar is derived from the National Grid for evaluation, in order to
investigate the potential of substitute forms of insulation used in later chapters of this thesis. This
design plan is developed while taking (400 kV) bus-bar into account with a (1425 kV) BIL
(although in some cases considered a lower BIL of 1050 kV). The radius of innermost conductor
along with outer sheath is 62.5 mm and 250 mm, respectively [59]. The gases pressure in bus-bar is
almost 0.3MPa.
2.9 Conclusion
2.9.1 SF6 properties and study model of gas insulated equipment
In this thesis, this chapter delineates the key properties of SF6 gas. SF6 is being implemented in
electrical networks worldwide as an insulating gas in switching and general circuit protection.
Generally, this gas has insulated equipment like GIS, GIL, and CB which are being installed in the
distribution network.
SF6 is the leading gaseous arc-quenching medium. The development of circuit breakers using SF6
clearly improved routines in present time and overcome the cost of oil filled and air-blast circuit
breakers, resulting in dielectric properties better than oil as well as air.
Furthermore, this chapter introduced equipment or devices which use SF6, especially for high
voltage (HV) substations like: HV and MV applications, transformers and switchgears.
17
Chapter 03
Merits and Demerits of SF6 Verses Alternative Gases
for Future Aspects
3.0 Analysis on Merit and Demerits of SF6 Verses Alternative Gases for
Future Aspects Characterization of Isolated Compounds
This chapter gives an in-depth analysis of the findings regarding the characterization of various
insulation gases and their significance in industry usage, while also discussing the merits and
demerits of their usage in high voltage equipment. In this chapter main focus is to analyze the
characterization of the widely used SF6 in insulation industry and its effects on global environment.
The study also highlights alternatives of SF6 gas along with their significance and limitations. The
study discusses R152a (gas) which is tipped to be the best alternative for SF6, so a detail literature
review of characteristics of R152a is discussed along with its variants while making an in-depth
performance comparison of SF6 gas with its alternatives and discusses why SF6 gas is superior to
alternatives in terms of insulation and performance.
3.1 Merits of SF6 Gas
This has been discussed in detail in previous chapter and is an ascertained fact that SF6 bears a high
dielectric strength while also having high electron affinity which boost itsability to quench an arc
during current interruption. These properties justify its use in current application in gas insulated
switchgear (GIS) [10, 60]. SF6 is a highly electronegative gas and its breakdown voltage is more
than three (3) times of air at normal pressure [20, 61]. In literature there have been different reports
on various mixtures of SF6 with other gases that have been tried so far for insulation applications.
These tried gases include different rare gases, hydro fluorocarbon gases, and SF6-N2 gas mixture.
SF6-N2 has shown good applicability for various HV applications including GIL [20, 58]. Hydro
fluorocarbons have got a superior dielectric strength over SF6 but their prolonged life in the
atmosphere renders them unsuitable for applications in insulation industry. For example, C â C4F8
is a worst choice for insulation because of its GWP of 12,200 with a dwelling moment in time of
3200 years in atmosphere [62].
18
3.1.1 Complications associated with the continuous usage of SF6
SF6 is first-rate absorber gas of infrared radiations (IR) and being a very stable and inert gas, it does
not leave earthâs atmosphere. This makes it one of the most dominant greenhouse gases these days
[62]. At the same time, it is also gentle to the ozone depletion because of its chemical inertness. The
gases or pollutants produced by the human beings in earthâs atmosphere are called anthropogenic.
The measurements of the greenhouse gases in the atmosphere are done in the units of parts per
trillion volume (pptv). SF6 was 0.03 pptv in 1970, which increased more than two folds in 1992
(2.8 pptv) with a predicted value of 65 pptv in 2100 if its consumption continues as it is today
[2,63].To date there is no active substituent for SF6 gas but as a probable solution of this problem, a
mixture of SF6-N2 has been proposed [61]. SF6 can sometimes produce very toxic chemicals on
coming in contact with an electrical discharge (e.g. S2F10 and SOF2).
Although SF6 usage has strict regulations in place and it does not get released in the air during the
electrical equipment life-cycle it is used in, still its yearly leakage rate of 0.1% has been reported
[1]. Because of the strict regulations under Kyoto agreement [64-65] about SF6 gas handling, its
removal and disposal are done separately by certified people thus increasing the cost considerably
[66]. According to Kyoto agreement every country must consider the release of SF6 gas in the
atmosphere as a severe problem. On the other side, the fluorine produced during the electrical
discharge in the switchgear equipment must also be accounted for.
Figure 3.1. Manufacture Compliances with impact of SF6 Regulation [64]
3.2 Ideal Properties of Alternate Insulation Medium
A new alternative insulation medium should have the following properties.
It should have low liquefaction temperature i.e. remains gas at low temperature
It should be thermally stable below 500ËC
19
It must have good arc quenching properties
It should not be flammable
It should not be explosive
Its breaking down strength should be of same level to SF6
Its GWP must be low
It should not be a good infrared absorber
Its Stratospheric measurement should be zero
It should possess low atmospheric lifetime i.e. decompose in the atmosphere easily
It can be used at high pressure
It must have no environmental impact
It must be a nontoxic gas
3.3 Gaseous Replacement for SF6 as Insulation Medium
3.3.1 Electronegative gases
The bond formed between two atoms as a result of sharing of electrons is called a covalent bond.
The shared pair of electrons in a covalent bond can be analogous to a tug â of â war in-between the
sharing atoms [67]. If one of these two atoms have different pulling force than the other, then the
electron pairs will remain closer to the atom which has greater pull on it. This will render some
ionic character to this covalent bond and make it polarized. These pulling forces of an atom towards
a shared pair of electrons are known as its electronegativity (EN) [68]. Conceptually, the
electronegativity can be understood in relation to the electron affinity and ionization potential of the
element.
The Ionization potential (IP) can be defined as âthe amount of energy required to eradicate an
electron as of its outermost shell of an atom in its isolated gaseous stateâ, thus a high value of IP
would render the donation of electrons difficult. The electron affinity (EA) describe as the amount
of energy released as an electron added to the last shell of an isolated gaseous atom. So, the higher
value of EA will mean the atom has more affinity to gain the electrons than losing them. So, if both
IP and EA are greater, the atom or element is said to be highly electronegative and vice versa [69].
Figure 3.2 depicts a portion of the periodic table showing the main group elements. As the elements
residing at the peak right corner of given periodic table have highest values of IP and EA, it makes
them highly electronegative as well. Fluorine (F) is considered to be the most electronegative
element in the periodic table with an electronegativity value of 4 on the scale given by Linus
Pauling. So, the presence of the electronegative elements, fluorine in our case, makes them
20
electronegative and polar as they pull strongly on the shared pair of electrons with their counter
atom.
Figure 3.2. Elements with its electronegativity [69].
3.3.2 Charge transportation and conduction in gases
Charge transportation and conduction in gases depend on different factors such as temperature,
pressure, electric field energy and the voltage across the electrodes of a container in which the gas
was placed.Each gas in row is normally a perfect and excellent insulator. For conduction in gases,
the following two conditions should be met.
Firstly, the gas in neutral form should produce charges otherwise accepted by its
external source applications
The external electric field should apply
Under the impact of the electric field, the charge carrier in the gas are positive or negative ions
which move freely. Conduction in gases is different from solid and liquid because in gases these
ions play vital role in the conduction of gas. Intended for any gas, there is a voltage level called
ionisation at which ionisationoccurs. The ionisation of gas occurs when gas molecule gains
sufficient energy and lose electrons and, in that ways, electron avalanche can occur leading to
partial breakdown, some condition it changes to complete breakdown.
3.3.3 Townsend's principle
In 1900 J.S Townsend produced his theory of breakdown and conduction in gases. Townsend
placed a gas in between two metal electrodes in a closed container vessel in his early experiment.
Variable DC voltage is supplied to the electrodes. Voltages gradually increase from zero to a
predetermined level. The electrode connected terminal with negative(-) side is denoted by cathode
21
as well as the terminal connected with positive (+) is represent by anode as revealed in figure 3.3.
Townsend found that the flowing of an electron depends upon the applied external electric field
[70].
3.3.4 Equation designed for growth current
Figure 3.3. Mechanism for Townsend discharge [70].
In figure 3.3 the distance between the electrodes is d, and the initial number of electron present in
the gap is No. voltage U is applied to the electrodes. The initial electron No gain sufficient energy
and move toward the anode. At length dx, the electron got a collission with the atom and form
ionisation and positive ions. Charge produced at a distance dx will be dn. According to Townsend
đŽđĄ đ„ = 0, đ = đđ
đ0 =numbers of electron emitted from cathode
đđ â đđđđ„
đđ = đđđđđ„
Equation 3.2 shows ionisation coefficient, which defined as the number of electrons produced by
ionisation.
đđ
đ= đ đđ„
Integrates both side
â«đđ
đ= đ â« đđ„
đ
đ
đ
đđ
This results in,
ln (đ
đđ) = đđ
Or
22
đ = đđexp (đđ)
đŒ = đŒđexp (đđ)
đŒđrepresents initial starting current.
3.3.5 Townsend's criterion for breakdown
1 â đŸ[đđ„đ(đđ) â 1] = 0
Ifd<ds, I=I0 if the supply is removed the I=0. If d is equal to ds I approach to infinity.
This called by Townsendâs criteria for breakdown and shown as:
đŸ[đđ„đ(đđ) â 1] = 1
Typically(ad) is huge, and so the above equation turns into
đŸ[đđ„đ(đđ)] = 1
In a certain partition of the gap and at some pressure(P) the value of the voltage(V) which results in
â ,Îł fulfilling the criteria of breakdown is known as the corresponding distance dsand spark
breakdown over voltageâs Vs are called by sparking distance.
3.4 Review of SF6 Alternatives
The exploration and progress to find much better replacement of SF6has been started research since
(1970s) that publicized that the mixed gases dielectric strength (DS) is better than pure SF6 gas [5-
10]. The inclination of SF6 emanation from electric equipmentâs started from the time of (1990s). In
the beginning, China was started the emanation of SF6 gas approximately 75% from its electric
equipment sectors [71].
3.4.1 Mixtures with SF6
Compared to the attachment process to prevent insulation from breaking down, in ionization
process the best dielectric control below their excitation efficient energy incorporates at lower
levels of electrons. In this regard, buffer gases such as nitrogen N2 oxygen O2, and carbon dioxide
CO2 are preferentially employed, because in all energy levels the additive gases cannot attach
electrons [72-3]. For example, above energies at 2 electron volts (eV), the attachment process of
these electronegative gases is more complicated. Consequently, the constituent gases are efficiently
mixed with extract energy from attaining electrons that wants to release beginning the lower energy
attachment region. As a result, the additive gases conception was used as an insulation purpose. A
research on the mixtures of SF6 such as (a) SF6+N2(b) SF6+CO2(c) SF6+Air is conducted in [46-52]
23
at various ratios to minimise the use of SF6. In [72] study of the particle was done in SF6/N2 but it
shows that the detection of the particle was more difficult in N2 from SF6. Figure 3.4 shows the
breakdown strength of SF6/N2 for different pressure and 50% breakdown revealed non-linear
behaviour.
Figure 3.4. SF6/N2 mixtures with different pressure.
3.4.2 Different alternatives of SF6
In [73] C2F6 was analysed and showed some good results, like its breakdown strength was equal to
0.90 times of SF6. Like SF6 it has also environmental concern because it contains high GWP and
high atmospheric lifetime. Also, it is costly and its price is 2.5 times of SF6 as shown in Table 3.1.
In [74] C3F8 was examined and showed nearly same breakdown strength to SF6, but it also
possesses high GWP and atmospheric lifetime. The price of C3F8 is double from the SF6.
In [75] CF3I gas was studied and showed good dielectric strength from the SF6 while also having
low GWP and atmospheric lifetime. CF3I was not economical because its price is 10 times of SF6.
In [76] 1-C3F6 was inspected and shows 0.97 times of breakdown strength and also has low GWP
and atmospheric lifetime but its price 3.5 times of SF6.
In [77] C-C4F8 was analysed and displayed good dielectric strength from SF6. It also contains
environmental and economic concern.
R152a shows good dielectric strength almost 0.96 times of SF6 and it also has low GWP and price
and it will be discussed detail in chapter 6 and 7.
24
R152a also have low GWP and price. It shows good dielectric strength approximately 0.88 times of
SF6 and it will be discussed in detail in chapter as well as 7.
Table 3.1. Comparison of SF6 with different alternatives [73-77].
Gas Chemical Name Breakdown
Strength
GWP Atmospheric
Lifetime
(years)
Boiling
Point
Cost/kg
SF6 Sulphur hexafluoride 1 22800 3200 -63â 25-30$
C2F6 Hexafluoroethane 0.90 12200 10000 -78.1â 2.5 times
đđđ đ Octafluoropropane 0.97 8830 2600 -36.7â 2 times
of SF6
Cđ đI Trifluoroiodomethane 1.21 5 0.005 -22.5â 10 times
of SF6
đđđ đ Perfluoropropylene 0.92 100 10 -29.6â 3.5 times
of SF6
đđđ đ Perfluorocyclobutane 1.21 8700 3200 -5.99â 9 times
of SF6
R12 Dichlorodifluoromethane 0.90 2400 12 -29.8â 0.50
times of
SF6
R134 Tetrafluoroethane 0.85 1300 14 -26.8â 0.33
times of
SF6
3.5 R152a Characteristics
R152a is recognized as a chlorofluorocarbon (CFC), which is commonly used in refrigeration
appliances and in aerosol sprays with properties in compliance with the Montreal Protocol [78].
R152a possesses some pertinent qualities making it an effective gas to be employed in the field; for
example, it is harmless and non-explosive. All these features make it a suitable candidate for
domestic and industrial usage as [79]. R152a (chlorofluorocarbon) has an appreciably lower value
of GWP: 140 and is a cheap contemptible insulation medium as compared to SF6.
25
Figure 3.5. Electronegativity of elements [78].
HCCH + 2 HF â CH3CHF2
Moreover, R152a has zero ozone depletion potential. As the atmospheric lifetime of R152a is 1.4
years so its decomposition products have 98% low environmental impact as compared to SF6.
Therefore, using the proposed gas mixture can effectively reduce the greenhouse effect.
Contrast between the physical and chemical properties of R152a and SF6is shown inTable3.2. It can
be prepared by reacting CCL4 (carbon tetrachloride) with HF (hydrogen fluoride) in the presence of
catalytic amount of (SbCL5) antimony pentachloride [80].
Table 3.2. Different properties of R152a [79-80].
Molecular formula CF2HCH3
Molecular weight 66.05 gmol1
Appearance Clear, Colorless liquid and Vapor
Odor Slight Ethereal
Density 0.90g/ccat (78 F) in liquid
Melting- point (MP) (-118âŠC or -180âŠF)
Boiling point -25âŠC (-13âŠF)
Solubility in water 0.28WT%@25C(77F) (87Pasia)
Vapor Density(air=0) 2.4
pH Not Applicable
Vapors- Pressure 89 pasia(26âŠCor 78âŠF)
Flashing Points Non
LEL/UEL 3.9%/16.9%
3.5.1 Physical properties of R152a
Chlorofluorocarbon R152a (CFC) is a colorless gas with a faint ether smell. Referred as a liquid
confined below, it does acquire vapor pressure. Contacts with unrefined liquid can cases frostbite.
Mutually components are incompatible [81]. It can asphyxiate by displacement of air, experience of
26
closed containers to prolonged heat or fire can foundation violent and rocket to explode. Different
physical properties are shown below.
âą Colorless gas with ether
âą Practically odorless, faint, ether-like odor in high concentration
âą Boiling point is -25âŠC(-13âŠF)
âą Physically gas at ambient temperatures
âą Flammable
âą Auto ignition temperature 850âŠF
âą Partition co-efficient n-octanol/ Water: Log Pow:1.13
âą Melting point is â179âŠF
âą Solubility is Insoluble
âą Solubilityinwater,0.28wt%at25âŠC
âą Density is 0.90g/cc at 25âŠC
âą Vapor density is 4.1 (Air =1)
âą Vapor pressure is 77âŠF
Thus, the material is stable. However, avoids high temperature and open flames.
Table 3.3. Contrast between physical along with chemical properties of R152a vs SF6 [80-81].
Properties SF6 R152a
GWP
Density
Relative molecular mass
24000
6.17 kg/mÂł
140
2.7 g/cmÂł
66.1
Atmospheric life 3200 1.5
Boiling point â64°C â25°C
Molar mass (g/mol) 140.6 66.05
Appearance Colorless Colorless
Permittivity 1.002 2.05
Electronegativity 2.5 2.32
Price/kg 28â30 $ 12 $
Water solubility Slightly soluble 0.276 g/l
27
Gas GWP
CO2 1
SF6 22800
R152a 140
Table 3.4. GWP of different gases.
3.6 Environmental Features of SF6, R152a and Gas Mixtures
Environmental characteristic of SF6 such as GWP, atmospheric lifetime and ozone depletion
potential of SF6, R152a and discussed.
3.6.1 Global warming potential (GWP)
A simple GWP index will be introduced and used here to determine the effects of the emissions of
the greenhouse gases in the atmosphere. This method is devised so you do not consider climate
change data (precipitation, temperature, wind, etc.) to be regionally determined, baseline discharge
scenario is problematic. In this (GWP) index, 1kg of the reference compound is related to the 1kg of
CO2 gas as developed by IPCC (1990) [82].
đșđđđđđ =â« đ đčđđđ
đđ»0
dt
â« đ đčđđđđđ»
0 dt =
â« (đđđđ»
0) đđ dt
â« (đđđđ»
0 )đđ dt (3.9)
Whereas
TH= Time horizon
RFcom= global mean radioactive forcing gas component
RFref = radioactive forcing
Ci =time dependent abundance of component gas
3.6.2 Atmospheric lifetime
It is defined as the time that a gas remaining in the atmosphere before it can decompose. SF6 is a
stable gas, therefore, it can take a large time to decompose in the atmosphere as shown in Table 3.2.
However, R152a atmospheric lifetime is less than the SF6 shown in Table 3.5.
The atmospheric lifetime concept has been established on the sample one box model and the
lifetime (T) of the specimen (X) which is in t box can be distinct as the molecule of the specimen
remaining in the box [82]:
28
đ =m
Fout+L+D (3.10)
Whereas Fout =leakage from the box, m= mass in kg, L= chemical loss of gas, D= deposition of gas.
3.6.3 Ozone depletion potential
In altitude, the ozone is 10-50 km placed in the stratospheric region. Ozone engages ultraviolet
radiation from the sun to the earth. Ozone depletion occurs from the man-made greenhouse gasses.
Ozone depletion is dangerous to the atmosphere because dangerous ultraviolet radiation comes
directly to the earth [82]. The ozone depletion potential of the SF6 gas can be said as negligible
because of its chemical inertness so it cannot react to the other gases in the stratospheric region [9]
[83]. R152a has small ozone depletion potential.
3.6.4 A Comparison of the dielectric strength of SF6 with alternative gases
According to the literature, the main cause of the SF6 insulation strength is the attachment of
electron [78]. It can capture free electron moving in the vicinity of the applied field to be converted
to an anion from the neutral SF6 molecule. SF6 + e â â SF â 6 (3.3) These resultant anions owed
to the attachment of free electron is heavy and do not move fast so they do not accumulate the
necessary energy for ionization. This procedure is very effective for the removal of free electrons to
prevent their accumulation to lead the circuit breakdown [79]. The above-mentioned process is the
competitor to the collision ionization process in which the electrons of a certain amount of energy
can inject electrons from neutral molecule to produce another free valance electron.
SF +( 6) + e â â SF +( 6) + 2e â (3.11)
Ionization of the gas is a process which continuously occurs in high electric fields thus producing
free electrons which can cause the breakdown of the gas. There are other gases having higher
dielectric strengths then SF6 gas.There are, however, other issues associated with the use of these
gases which include (but not limited to) toxicity, limited range of operating pressure, production of
pure solid carbon, etc. Thus, SF6 is merely gas which has been established and used in GIS
applications [82].
3.7 Conclusion of Gaseous Replacement for SF6
The different types of gases that could be utilized as insulation medium for voltage insulations
prospects are presented in this chapter. In the case of high voltage insulation, the dry air and N2 can
be utilized as a substitute to the SF6. But this requires very high pressure in order to yield the same
29
insulating characteristics as possessed by SF6. The authorâs developed R152a gas and its gaseous
mixture possessing the promising performance that can replace the SF6 is presented. In addition to
this, a wide range of calculations have been presented that validate the performance of R152a are
presented.
30
Chapter 04
Leakage of SF6 Gas from Power Plants
4.0 Introduction
In this chapter, the worldwide usage of SF6 gas as insulation medium will be illustrated. Equipment
that uses SF6 gas as insulation medium is also examined. Leakage of SF6 from already installed
equipment in the distribution network will be discussed in this chapter.
4.1 SF6 equipment review
To understand the worldwide role of SF6, it is necessary to analyse that how SF6 has been employed
in the past. It is also compulsory that why theparticular design of SF6 was applied such as contact
design. From the past and today familiarity with accustomed distribution networks, with the today
use of SF6equipments, can be investigated that how needs of SF6 replacement can be a tackle.
In 1980, SF6 was firstly familiarised and used in power industry as an insulation medium and then
gradually adopted by the electrical network for insulating various equipment [83]. From Figure 4.1
it can be clear that SF6 was used for all voltage level while the insulation medium cannot use for all
voltage levels. SF6 can use up to 800 kV, while another medium cannot use for such high voltage
apart from compressed air which can be used with a high electrodes gap distance. SF6 can also be
used for arc interruption and so it can be used to break high current interruption medium.
Figure 4.1. Insulation medium and its voltage ranges [83].
0 200 400 600 800 1000
Air
Compressed air
oil
SF6
Voltages (kV)
Voltages (kV)
31
Figure 4.2 shows the use of SF6 and other insulation medium from 1982-1998 in Europe and the
figure indicated that the use of SF6 increased rapidly due to its good properties. The use of other
medium decreased day by day because of limitation of air and oil. Oil properties become degrade
due to ageing and air requires more space due to its less breakdown strength. On the other side,
SF6requires less maintenance and has a high life.
Figure 4.2. Medium voltage circuit breaker usage [84].
Figure 4.3 illustrates the dependency of interelectrode distance on dielectric strength. For air, the
distance between electrodes is increasing more to maintain voltage level [85]. Therefore, the size of
the equipment will also increase and also taken more space. On the other side, SF6 space between
the electrodes is less for HV and EHV.
Figure 4.3.Dielectric strength dependency on inter-electrode distance [84].
0
10
20
30
40
50
60
70
80
90
100
1982 1984 1986 1988 1990 1992 1994 1996 1998
SF6 Vaccum Oil Air
0
100
200
300
400
500
600
700
5 10 15 20 25 30
SF6 Oil Air
32
In low voltage distribution network, air circuit breakers are used more dominantly because it is less
than the other insulation medium at that level [82]. In EHV SF6 was the only medium to use at that
level because it takes less space and also no other medium can be used at that level [12].
4.2 Utilization of SF6 Equipment in the Distribution Network
In Figure 4.4 the distribution network is shown, in which the use of SF6 is mention at all voltage
level. The main equipment which uses SF6 as an insulation medium is GIS, GIL, and the figure also
shown at a low voltage another insulation medium can be used.
Figure 4.4. Classical distribution network [12].
In Figure 4.5, the schematic diagram of distribution network is shown which also gives the range of
low, medium and high voltages.
33
Figure 4.5. SF6 usage in distribution network [12].
In Table 4.1, several switching devices and their function are given. The function of several devices
at different circumstances are described in Table 4.1.
4.3 Worldwide SF6 Usage and its Effects
It is a well-known fact that gases cannot be contained in a closed vessel, according to IEC 62271-1
standard there will be 0.1% leakage from any closed vessel. Data is accumulated for 25 years on the
basis of 0.1% leakage of gases worldwide. This database does not contain leakage of gas from
handling processes or any containment failure in gas chambers. The percentage leakage ratio can
vary depedning upon usage and age of equipment and standards.
In power systems ring main units are installed in switch yards of grid stations these ring main units
are metal enclosed switch gears and in GIS system their insulation is SF6 gas and as per table 4.1
there are 2,322,600 RMUâs (Ring Main Unit) installed worldwide. If we consider 0.6 kg of SF6
used in each RMU then the total would amount to 1,393,560 kg and now if we consider 0.1%
leakage of gases as per IEC standard then the leakage of SF6 gas would amount to 34,424 kg in 25
years which is a significant figure.
34
Table 4.1. Several devices and their function.
Task Opening Closing
No
load
Loadconne
cted
Fault No
load
Load
connected
Fault
Disconnector Mechanical
device and
it will be in
open
position
under
unsatisfact
ory
condition.
yes No No yes No Yes
Switch Opening
and closing
of a circuit.
yes Yes No Yes Yes Yes
Earthing
switch
Safe
isolation of
a circuit
under
uncertain
condition
yes No No Yes No Yes
Contactor A
mechanical
device, it is
basically
for motor
control.
yes Yes No Yes Yes Yes
Circuit
breaker
The
isolated
circuit in
afault
condition.
yes Yes Yes Yes Yes yes
35
Table 4.2. Worldwide usage and leakage of SF6 from all RMUâs [83].
Number of
worldwide
SF6 insulated
RMUâs
Expected SF6
Mass of each
component
Total SF6 used
in all RMUâs
Annually
leakageofSF6
from all
RMUâs
Cumulative 25
years
SF6leakagesfrom
every single one
RMUâs
2,322,600 0.6 kg 1,393,560 kg 1,376 kg 34,424 kg
The Same calculation is taken for SF6 insulated circuit breaker used in all over the world. There are
600,000 of SF6 insulated circuit breaker used worldwide. If 0.35 kg of SF6 is used in each CB then
thetotal amount of SF6 used in all CB is 145,000 kg. If the same leakage ratios are considered then
the 25 years leakage of SF6are 34,424 kg as shown in Table 4.3.
Table 4.3.Worldwide SF6usage and leakages from every CBâs [83].
Number of
worldwide SF6
insulated CBâs
Expected SF6
Mass of each
component
Total SF6 used
in all CBâs
Annually
leakages SF6
from every
CBâs
Cumulative 25
years leakages
SF6 from
every CBâs
600,000 0.34 kg 145,000 kg 150 kg 3705 kg
In Table 4.4 worldwide use of switches are given and if 0.429 kg of SF6 is used and the leakage
ratio is considered same then the 25-year cumulative leakage of SF6is 7178 kg.
Table 4.4. Worldwide usage and leakage of SF6 from all switches [83].
Number of
worldwide
SF6insulated
Switches
Expected SF6
Mass of each
component
Total SF6
used in all
Switches
Annually
leakageofSF6
from all Switches
Cumulative 25
years leakages SF6
from every
Switches
677,400 0.429 kg 290,604 kg 287 kg 7178 kg
36
In table 4.5, a total amount of SF6 is used in every one RMUâs, CBâs and switches are shown.
Table 4.5. Total amount of SF6 use in all RMUâs, CBâs and switches [83].
Number of
worldwide
SF6
insulated
RMUâs
Number of
worldwide
SF6insulated
CBâs
Number of
worldwide
SF6insulated
Switches
Total SF6
used in
every one
MV RMUâs,
CBâs &
Switches
Annually
leakages SF6
from every
MV RMUâs,
CBâs &
Switches
Cumulative 25
years leakages
SF6 from every
MV RMUâs,
CBâs &
Switches
2,322,600 500,000 677,400 1,834,164 kg 1,812 kg 45,308 kg
From figure 4.6 it is shown that use of SF6 in GIS is very popular in distribution networks which are
63% of all the worldwide SF6 usage followed by CB and GIL. There are 20,000 unit of GIS
installed in all over the world and if 500 kg of SF6 is used in each unit then the total amount of
leakage from all GIS is 247023 kg as shown in Table 3.6. Table 4.7 shown that 30000 km of GIL is
installed in worldwide and 30.24 kg is used in each km of GIL and the total leakage is 22410 kg.
Figure 4.6. Percentage wise use of GIL, GIS and CBâs.
Table 4.6. Worldwide usage and leakage of SF6 from all GIS [83].
Worldwide SF6
insulated GIS
Expected SF6
Mass of each
component
Total SF6
used in all
GIS
Annually
leakage ofSF6
from all GIS
Cumulative 25 years
leakage of SF6 from
all GIS
20,000 500 kg 10000000 kg 9881 kg 247023 kg
GIL6%
GIS63%
SF6 CBâs31%
GIL
GIS
37
Table 4.7. Worldwide usage and leakage of SF6 from all GIL [83].
Worldwide
SF6insulated
GIL
Expected SF6
Mass of each
km
Total
SF6used in
all GIL
Annually
leakageofSF6 from
allGIL
Cumulative 25 years
leakage of SF6 from
all GIL
30,000 km 30.24 kg 907184 kg 896 kg 22410 kg
Data regarding usage of SF6 gas worldwide in distribution networks is shown in figure, Figure 4.7
this figure shows a 0.1% leakage of SF6 gas [1] in all metal enclosed distribution equipment
worldwide over last 25 years [84]. Figure 4.7 shows that High voltage GIS metal enclosed
equipment with SF6 to be used as insulation medium releases 247023Kg of Sf6 gas into atmosphere
over the period of last 25 years [85]. For each of these mentioned results an equivalent ratio of
emission of carbon Dioxide gas for every 1 KG of Sf6 gas released is also calculated which
amounts to 23,900 kg of CO2 being released into the atmosphere.
Figure 4.7. Estimated 25-year leakage of SF6 worldwide distribution equipment [86].
It can be calculated from Figure 4.7that the worldwide leakage of Sf6 gas from all HV and MV SF6
equipment at distribution stations over a 25-year period is approximately 438 tons of SF6 gas which
is the equivalent of 10468 kilotons of CO2. According to [85-86] it has been estimated that
34453427 kilotons of CO2 was released into the atmosphere in 2012 alone.
Conclusion
The main high voltage equipment that utilizes SF6 as an insulating medium in the world, is
presented in this chapter. The problems estimating the leakages of SF6 in these items of equipment
38
are also analyzed in this chapter. The estimated problems are also presented while comparing with
the CO2 in an equivalent ration. The leakage problems in such equipment at the time of installation
as well as during the operational life of these equipment is also analyzed. The wide range of
calculations are presented in order to validate the R152a as a substitute to SF6. These calculations
do not involve the leakage of SF6 due to mishandling of equipment or gas chamber failures. As the
data shows emissions of SF6 is not large compared to CO2, but due to long lifetime of SF6 gas it is
potentially more harmful to environment as than to CO2 in the long run.
39
Chapter 05
Development Test, Laboratory and Investigational
Methodology
5.0 Introduction
This chapter describes the applied experimental procedures, equipment and test specimen. In
Section 5.1 exemplifies the detailed report and explanation of the equipment, test setup and
different gases mixtures which are being used for breakdown tests. Furthermore, electrodes
installation for these breakdown tests depict in 5.2 section. The breakdown procedure of these
gaseous mixture is also express. Section 5.3 and 5.4 are briefly explain parameters which corelate
for test procedures. To end with, 5.5 Section are describing the tests equipment, material samples
procedures as well as material characterization.
5.1 Laboratory Setup and Assembly of Test Electrodes
This section describes the experimental test setup in HV laboratory, techniques applied and
assembly used for test electrodes. Figure 1 shows the experimental setup in which the
manufacturing on the IEC60270 standard [89]. The test setup consists of a control desk (HV-9103)
comprising a peak voltmeter (HV- 9150) plus built-invariable voltage supply. The power supply
output is 0 to 230 volts and the voltmeter peak range is 100 to 1000 (kV). The control desk consists
of measuring instruments, namely Impulse, Peak, Trigger devices and DC Voltmeters. Using a
voltage doubler circuit, the rectification of AC is performed in case of DC voltage application
where upto 140 kilo Volt DC voltage be able to generate.
During experiment whenever breakdown occurs, voltmeter measures the breakdown voltage across
the measuring capacitor. Prior to starting the experimental breakdown voltage tests, AC Voltage of
identified value was applied to a voltmeter and measuring devices for calibration purposes to
minimize errors and improve precision. All experimental results were obtained at room temperature
(20-25â). The pressure vesselâs temperature rise has been avoided by the interval of 5 mins
between two consecutive breakdowns as recommended in [90].
40
Figure 5.1. Experimental set up to examine R152a/CO2 breakdown voltage by Sphere-Sphere electrodes.
(a)
(b)
(c) (d)
Figure 5.2. Test equipment used: (a) Control and measurement unit(b) Testing vessel (HV-9134) (c)
Experimental setup for DC (d) Spark formation comparison.
The testing vessel for vacuum and gas is made of steel and equipped with a pressure gauge to
measure pressure up to 6 bars. The manufacturing material of the electrode was aluminum enclosed
41
with a nickel coating. The diameter of the electrodes is basically 50 mm. Electrode diameter was
selected to be 50mm because the gap length should be equal or less than the radius of electrode to
maintain uniform electric field. In our experimental work the gap length is varied from 0-16 mm,
therefore 50 mm is best appropriate diameter of electrodes. Subfigure5.2 (a) is a Control and
measurement unit. Subfigures 5.2 (b) &5.2 (c) show Testing vessel (HV-9134) and experimental
setup respectively. The vessel contains a cylinder made of Plexi-glass that is sandwiched with
flanges top and bottom which are linked with high voltage (HV) and ground potential
correspondingly. The bottom cover is furnished with essential apparatus, such as inlet or outlet
valves measuring gauge intended for vacuum and pressure. Specifications of the test vessel
provided by the manufacturers are briefly described in Table 5.1. As shown in Subfigure 5.2 (d)
Spark tends to suppress and turns into a bluish glow.
Table 5.1. Test setup specifications.
Specifications Standards
Voltage (AC) 100 kV
Pressure (p) 0 to 6 bars
Diameter of Sphere Electrodes 50 mm
Vertical Height 800 mm
5.2 Insulating Material Breakdown Voltage
To calculate the relation between Electrical break down voltage and fields strength with the gap
length d for homogeneous fields, following Equation is used:
dEU dd. (5.1)
Electrical breakdown voltage and breakdown fields always depend on AC and impulse voltage due
to the short-term effect of Electrical breakdown. Sometimes excessive short-term stresses in
seconds or minutes are enough to generate electrical breakdown but it can be happened after some
hours, days, or year due to long term aging effect. In atomic configuration of insulting materials, all
valence electrons are tightly bounded with the central nucleus. When an external voltage is applied
to this insulating material, an electrical pressure is developed that pulls electron out of valance bond
and electron flow starts. Being an insulating material, it resists the flow of valence electron. This
type of material is called dielectric and It is used in many Electric circuits just to distinguish the
function off different conductors within the circuit without conduction inward [91-92]. So,
42
breakdown voltage is a key characteristic of an insulator material that describes the limit of
maximum voltage to be applied across an insulator before its conduction.
5.3 Breakdown of Gases
At normal temperature and pressure gases are excellent insulators with the conductivity of 10â10
A/cm2. This conductivity is due to the air ionization of cosmic radiations and radioactive elements
in the atmosphere. The charged particles get efficient energy during collisions in the high electric
field intensity region to cause ionization. During these collisions electrons lose their energy and get
a kinetic energy by the external voltage source. This kinetic energy s converted to a potential energy
by the ionization. This ionization is actually a name off process that pulls electrons away from the
bounded shells and leads to a breakdown of gases. In photo ionization, radiation energy is an
external source that affects the ionization energy of electrons A+ hÎœ â A+ + e where A represents a
neutral atom or molecule in the gas and hΜ the photon energy. In photo ionization process, if photon
energy is not sufficient to remove the electron from the shell then it jumps to the higher energy level
or shell. T s called photo excitation [93].
Gases are more common dielectric materials. Air is used as insulating medium for most of the
apparatuses but in some cases following gases N2, CO2, R152a and SF6 (hexafluoride) are used.
Dielectric gases pass through various stages when an external voltage is applied. A small current
flow with the low voltage application across electrodes off the dielectric material and it retains its
electric property. High voltage causes a sharp increment of current in the dielectric materials that
leads to breakdown. This breakdown property in gases depends on electric properties.
There are two types of electrical discharges in gases.
Self-sustaining types
Non-sustaining discharges
Electrons in different shells around a nucleus of an atom are strongly bounded. Stronger the bond
with the complete shell, stronger will be breakdown strength. Electrons are heavy ions like positive
ions. They get much energy from collision that makes their bond weak with nucleus, so low voltage
is enough for ionization for flow off current. The types of gaseous attachments that play attractive
and active role are called electronegative gas.
a) Direct attachment: An electron directly attaches to form a negative ion.
AB + e =>AB
43
b) Dissociative attachment: The gas molecules split into their constituent atoms and the
electronegative atom forms a negative ion[95].
AB + e => A +B-
Oxygen is a simplest example of this type off gaseous attachment. Others are others are Sulphur-
hexafluoride, Freon, carbon dioxide and fluorocarbons. In the equations presented above, âAâ
representseither sulphur or carbon atom while âBâ is representing that it can be either oxygen atom
in these gases or one of the halogen atoms / molecules. In high voltage power equipment,SF6, N2,
CO2, R152a are various insulating materials that are used [96].
The charge carrier collisions in gases and interaction with the electrodes cause breakdown
mechanism. In principle, free electrons are accelerated inside the gas filled gaps by the electric
field. The collision of free electrons with gas atoms is shown in Fig (5.3)[97]. These free electrons
collide with gas atoms and if they have sufficient energy, they release more electrons. An avalanche
of electrons can grow towards the anode, while ions that move in the opposite direction can collide
with the cathode generating new electron. In microseconds, a conductive breakdown channel is
developed with this mechanism. Photon emission mechanism is used for large distances gaps for
plasma formation. Streamer-Leader process measures bridging of long gaps in meter range.
Figure 5.3. Discharge (breakdown) development in a gas volume between two electrodes by electron
avalanche process[97].
The specific effects taken into account are following:
The strongly inhomogeneous electrical field approaches to high fields
close to the curvature and lower field strengths in the remaining gap
space. This electrical field assumes a curvature that has smaller
radius.Thus, with the increase of voltage up to a certain threshold, level
locally the breakdown field strengths at the curvature and it in results in
the local limited discharge happenswithout having a full breakdown.
The âexternal partial dischargeâ or âcorona is the specific regard given
UD
E
44
to the limited discharges[98]. The permanent current pulses that are
effective as a leakage current are also caused due to the existence of
corona. The corona results in the visible glow andrelated leakage current
increase with the further increment of voltage. The corona is in a
position to extend into the zone of lower field strength at critical
voltage. Thus, it finally bridges the gap that results into a full
breakdown [99].
Space charge formation causes a polarity effect for unsymmetrical
inhomogeneous fields, leading to the following consequences.the corona
starts with the lower voltage, if the electrode with the stronger curvature
is at a negative potential. However, the breakdown voltage will be
higher in comparison to the case with the electrode of the stronger
curvature is positive. This is representing no corona or corona at voltage
close to breakdown) [100].
The breakdown voltage is affected by the electrode surface due to the effect of
surfaceroughness (local field enhancements).
The breakdown strengths are reduced by placing a sold insulator
between two electrodes as surface layers i.e. water or contamination can
varythe distribution of electrical field enormously. This effect is
partially or fully compensated via enhancing creep-age path lengths of
an insulator [101][98].
The breakdown strength is affected by the âtriple-junction areaâ in the
corner between two metal electrodes and insulation media.
The gaseous insulation is generally regarded as self-healing. The main
cause for this because after compensating and reapplying the power
source the insulation recovers to its initial strengths [102][98].
5.3.1 HVAC test arrangement for breakdown voltage
Mostly in present days transmission networks and distribution are operating under (AC) voltages
furthermore, typically the linkage of testing apparatus with high voltages (HV) in AC forms [103].
UD- > UD+
45
In any system mostly equipment is 3-phase, either single- phase transformers, they must operate at
power frequency for High Voltage (HV) AC testing bench [104].
5.3.2 HVAC Arrangement for breakdown voltage
AC analysis laboratory circuit is arrangements revealed in Figure 5.4. During these experimentsâ
AC voltage is applied with variation of pressure on pure R152a gas as well as R152+CO2 f. These
experiments are performed with electrodes gap of 6mm and 10mm and electrodes with 20mm
diameter Electrodes with 20mm diameter. For an unchanging pressure voltage is changed unless
breakdown occurs also same work repeated for fix temperature. Ten to hundred readings are taken
for each pressure value after that Mean value calculated by applying different formulas. The special
elements like measuring capacitor along with peak voltmeter used for AC testing. For high Voltage
AC test illustrate in Figure 5.3 with schematic diagram [105].
Figure 5.4. Schematic diagram for AC test.
Figure 5.5. AC Experimental Setup.
46
5.4 HVDC Test
A large number of applications for high DC voltages are in electric industries as well as in medical
sciences research [106]. HVDC transmission system has become a very famous choice for overhead
lines moreover for underground cables. HVAC cables are tested by HVDC of long lengths as they
possess very large capacitance.These would require very large values of currents when tested on
HVAC voltages because of presence of large capacitances [107-108]. The D.C tests on A.C cables
are reliable and economical but they in these tests the stress distribution within the insulating
material varies from the routine operating circumstances. The electrostatic precipitation especially
in thermal power plants, cement industry, electrostatic painting, communication systems is also
performed by utilizing this test and validated results [109]. HVDC is also extensively being used in
medical equipmentâs like (X-Rays) and in physics for particle acceleration [110]. Rectification
employing voltage multiplier circuits are used to produce high D.C. voltage efficiently. High D.C.
voltages are also used to produce Electrostatic generators.
5.4.1 HVDC arrangement for breakdown voltage
The generation of DC voltage from AC voltage is from voltage doubler-circuit. The setup available
in the laboratory can produce C voltage up to 140kv. Figure 5.5 is schematic diagram and
laboratory experimental setup for DC tests shown in Figure 5.6. Breakdown of the gas occurs by
increasing voltage at a fix pressure. For all pressure value, hundred different values of HVDC
voltages are being apply in addition to calculate average value by using different mathematical
tools. Every part of results is measured plus sketched in graphically also represents in schematic
diagram blow [111].
Figure 5.6. HVDC test represents in schematic diagram.
47
Figure5.7. DC Experimental Setup.
5.5 List of Equipment Used in Experimental Tests
Following is the list of equipment required for experimental testing of the gases with spherical
electrodes.
1. Testing transformer for high voltage.
2. Control desk.
3. Measurement capacitor.
4. Voltmeter for measuring AC.
5. Rod for connecting equipment.
6. Cup for connecting.
7. Rod for Earthing.
5.5.1 Control desk
Table 5.2. Descriptions of Control desk.
Supply âVoltage (220-230 V), (50/60 Hz), (25 A single phase)
Regulating-Transformer (5kVA), (Geared motor drive) DC
Regulating âVoltage (0-220 V) AC
Output (5kVA Continuous), (10kVA), (2min short time duty)
Dimension (1220x105x800mm) (hxwxd)
Weight (275 kg)
48
High voltage (HV) tests AC as well as DC equipment are operated through control unit, it also
measured real values which one recorded in unit. In control desk unit numerous elements
assembled, like control, operational, safety point of view furthermore warning signal. every single
one measuring instruments Impulse and peak voltmeter, DC voltmeter, as well as triggering devices
are entrenched in this control unit. Above Figure 5.1a epitomize the control unit with brief
descriptions exposed in Table 5.2.
5.5.2 Pressure/vacuum vessel (HV 9134)
Technical data
AC Voltages (100kV)
Impulse Voltage DC (140kV)
Operating pressure (0-6 bar)
Diameter of Sphere Electrodes (20 mm)
Height approximately (800 mm)
Weight of vessel (12 kg)
Figure 5.8. Vacuum/pressure Vessel.
5.5.3 Applications
Vessel made by Plexi-glass cylinder rigid with top plus bottom flanges connected to ground
potential and high voltage (HV) correspondingly. The floor cover is prepared by obligatory
49
accessories, like inlet/outlet valves, also pressure along with vacuum measuring gauges. Earthing
terminals are endowed with bottom pedestal. The (50 mm) sphere -electrodes are mounted seeing
that in Figure 5.8.
5.5.4 Test transformer (HV 9105)
Ratio of T/F (2x220V) (100kV) (220V)
Rated current Continuous (2x11,4A) (50mA) (15.2A in Continuous)
T/FImpedance Voltage At (100 kV)< 3pC.
Partial Discharge (PD) Level (5 kVA) (10kVA) for 60 min.
Frequency (50Hz/ 60 Hz)
Weight 215 kg
Diameter 550 mm
Figure 5.9. Test Transformer.
5.5.5 Applications
Test transformer(T/F) winding for coupling cascade connection, which one generate high voltage
(HV)Alternating Current as revealed in figure 5.9. Transformer made with three windings by
insulating shell along with apex and base corona for free Aluminum electrodes.The primary
windings are a double winding(2x220V) for connecting t parallel connectionof 22o volt, in series
connection (220 +220V) connecting with. High voltage(HV) secondarywindingsin series of 100 kV.
"Coupler Windingâ also known as third windings which supplied to cascade connections in
transformers.
5.5.6 Peak voltmeter (HV 9150) for digital display
Supply voltage (220 V 50 Hz)
Measuring Range (100-1000 Ă / â2 kV)
Dimension (142 x 173 x 245) (WxHxD)
Weight (3.4 kg)
50
Figure 5.10. Peak Voltmeter (PV).
5.5.7 Applications
Compressed Gas Capacitor or Coupling Capacitor use for measurement of peak (AC) connections.
We employ (HV 9114) for earthing switch which one electrically function as revealed in figure
(5.10).
5.5.8 Discharge Rods
Figure5.11. Discharge Rod.
5.5.9 Applications
High Voltage (HV) discharging for manual component as revealed in figure (5.11).
5.5.10 Aluminum (HV 9108) Rod Connecting
Figure 5.12. Connecting Rod.
Discharge -Resistance (100Ω)
Rod -Length (2.5m)
Rod-Weight (2.5 kg)
Rod span (660 mm)
Rod Weight (2.04 kg)
51
5.5.11 Applications
The connection conductive elements as revealed in figure (5.12).
5.5.12 Aluminum (HV 9109) cup connecting
Figure 5.13. Connecting aluminum Cup.
5.5.13 Applications
5.5.13.1 Conductive Elements
Two(2) elements are capable of being placed in the vertical position as well as four(4) elements are
capable of being inserted in the horizontal position as revealed in figure (5.13).
Dimensions (h 85 Ă x 150 mm)
Weight of cup (2.2 kg)
52
Chapter 06
Experimental Results of R152+ CO2 Mixtures: as a Potential
Alternative to SF6
6.0 Introduction
In this Chapter mathematical as well as from tentive experimental opinion, the performances of
R152a incorporate explicitly correlated saturated and superheated properties in comparison with
existing insulating materials are presented. The experimental study of power frequency breakdown
voltage is also analyzed for a proposed gaseous mixture of R152/CO2 comprehensively discussed
in this chapter
6.1 Power Frequency Breakdown Voltage Experiments and Results
6.1.1 Experimental procedure
Prior to start testing, both electrodes were cleaned with alcohol dumped silk textile cloth to eliminate
moisture and impurities to minimize errors and maximize accuracy in all observations. Tests were carried in
dried and moisture-free zone at room temperature. An increase in temperature raises the probability of errors
in experimental results. To overcome this problem, time span for each test was restricted to 15â20 min. As
R152a and CO2 both are inert and in gaseous form, the time equal to 30â45 min is enough to mix properly
for both gases [112].
6.1.2 Gas mixture procedure
Considering the proposed alternate gas mixture liquefaction temperature experimental constraints
and different mixture ratios for power frequency breakdown voltages were mentioned in Tables 6.1
and 6.2.
Table 6.1. Experimental constraints.
Configuration of Electrodes SphereâSphere
Length of spark gap 6mmâ18mm
AC voltage 0â100 kV (Peak)
DC voltage 0â140 kV (Peak)
Material of electrode Aluminum /Ni plated steel
53
Table 6.2. Different mixture ratio of R152a and CO2.
Measurement No. R152a Ratio (%) CO2 Ratio (%)
1 90 10
2 80 20
3 70 30
4 60 40
5 50 50
6.2 Calculation of Accurate Gas Mixture Pressure
In order to fill up the accurate amount of R152a and CO2 to achieve the accurate ratio of the gas
mixture by P/P, the calculation of the amount of gas required is essential. A notable thing here is the
P/P ratios of the mixtures of gases because using the W/W ratio would render the calculations
incorrect as the molar mass of molecules can change the pressure of the gas mixture heavily. The
total amount of R152a and CO2 needed is calculated by means of the ideal gas law seeing that in
Equation (6.1) below [113].
đ =[đ Ă đ Ă đ]
[đđ Ă đ]â (6.1)
Where:
m = Mass in (grams)of gases,
P = Gases Pressure into (bars),
T = Gases High Temperature in (Kelvin),
R = It belongs to Ideal gases constant,
MW =It presents the Molecular weight of gases in (g/mol),
V = Gases Volume in (liters).
For example, in R152a process, the gas accurate temperature was (20°C). The ideal gas constant (R)
=0.083also MW of R152a = 66.01(g/mol) and MW of CO2 = 44.02(g/mol). Consequently, when
chamberfilled by mixture volume of each gas be able towell calculated as follows below [114]:
đ =[đ Ă đ Ă đ]
đđ Ă đâ = 1300Ă0.0821Ă293/146Ă1.4 = 153 L
In order to fill 80% R152a required amount of this gas
54
đ = đđ Ă đđ đ â = (66Ă0.98Ă153)/ (0.0821Ă293) = 412 g
Similarly, for 20% amount of CO2
đ = đđ Ă đđ đâ = (44Ă0.42Ă153)/ (0.0821Ă293) = 117 g
Therefore, the amount required to fill 80%/20% mixture ratio of R152a/CO2 is 412:117g.
6.3 Mixture Ratio Analysis
Experiments were performed to locate power frequency breakdown characteristics on8mm
electrode distance under these environments (a) pure R152a, (b) pure CO2, (c) CO2 (50%) with
addition of R152a (50%), (d) CO2 (40%) with addition of R152a (60%), (e) CO2 (30%) with
addition of R152a (70%), (f) CO2 (20%) with addition of R152a (80%) and (g) R152a (10%) with
addition of R152a (90%). Figure 6.1 shows the breakdown strength of R152a and CO2 among their
mixture at different R152a/CO2 ratios.
Figure 6.1. Power frequency breakdown voltage of R152a/CO2 gas at varying mixture ratio and 8 mm
electrode gap distance.
R152a is an electronegative gas, moreover all negative (-) ions are created by gaining electrons
from neutral molecules, which as a result become positive ions after losing electrons. Gaining and
losing of the electrons could occur depending on the field applied and attachment and detachment
capability of the insulating medium. Losing electrons or detachment coefficients is symbolized by η
55
as shown in Equation (6.2) [114]. When a single electron travels per unit length, several electrons
produced in that specified path are defined by Townsend first ionization coefficient, α.
dN = N (α â η) dx (6.2)
where N refers to initial electron quantity, dN denotes the no of electron traveled a distance dx.
6.3.1 Dielectric strength analysis
The breakdown strength of R152a and CO2 different mixtures was measured in uniform field under
AC voltage. Figure 6.2 displays the dielectric strength characteristics which can be attained by
ratios of 80% and 20% respectively on 4 bar which gives the highest breakdown strength of 96% of
SF6 gas.
Figure 6.2. Breakdown characteristic comparison of R152a/CO2 gas at 80%/20% mixture ratio and SF6 at 8
mm electrode gap distance.
6.4 Gap Difference Analysis
The breakdown voltage of R152a/CO2 gas varied with the electrode gap distance (4â16 mm). This
gap between both electrodes has dominant effects on the gas dielectric strength as shown in Figure
6.3. In Equation (6.3) there is an almost linear relationship between the electrode gap and
breakdown voltage as can be seen [115].
đž = đ â (đ
đ·)(6.3)
56
wherever constant (f) is representative non-uniformity, while (V) is applied voltage as well as (D) is
distance flanked by two electrodes. R152a/CO2 (80%/20%) revealed a similar growth trend as SF6
by changing the gap length as shown in Figure 6.3. After 12 mm, no significant improvement in
breakdown voltage was found for other mixtures of R152a/CO2.
Figure 6.3. Breakdown voltages of R152a/CO2 gas varying the gap distance (4â16 mm) at different mixture
ratio.
6.5 Statistical Analysis of R152a
Table 6.3 demonstrates the statistical analysis of R152a along with CO2. These are premeditatedly
designed for variable magnitudes of two mixed gases. The experimental values like coefficient of
variation, (SD) standard deviation in addition to mean deviation are depicted in mentioned Table
6.3 that demonstrates the discrepancy of results are accomplish through the experiment. The SD of
R152a and CO2 (70%/30%) shows a rapid variation in value. Correspondingly, coefficient of
variation is observed at the lowest value at (90%/10%) mixing ratio and the mean deviation was
found lowest value at (60%/40%) in Table 6.3.
Table 6.3. Statistical analysis of R152a.
Base Gas R152a Mixed Gas CO2
RBG1 50% 60% 70% 80% 90%
SD 11.2 12.3 10.21 14.2 12.9
Î 46.1 51.6 59.7 57.3 55.3
cv 0.23 6 0.27 0.28 0.19
Max kV 60 69.8 73 76.1 71.6
Min kV 26 4 49.8 43 35.6
57
6.6 Global Warming Potential (GWP)Analysis
This novel alternative R152a/CO2 gas mixture has been particularly developed to significantly
reduce GWP as compared to SF6. According to environmental protection view, the GWP is
calculated as a weighted average of this proposed gas mixture, and from the sum of the weight
fractions of mixed substance and multiplied with their individual GWP as given in Equation (6.4)
where k shows the base gas mixing ratio, 140 is the GWP of R52a and 44 and 56 is the molar mass
of R152a and CO2 respectively [116-118].
đșđđ =(đĂ56Ă140)+(1âđ)Ă44Ă1
(đĂ56)+(1âđ)Ă44 (6.4)
The relationship among GWP value plus mixing ratios is shown in Figure.6.5. It is found that
R152a/CO2 mixture contents with ratio 80%/20% at â14.16°C has a total GWP of 117.17 instead of
22,800 of SF6 over a 100-year time span, effectively reducing the greenhouse effects by 98%.
Figure 6.4. Global Warming GWP analysis of R152a/CO2 gas mixture.
6.7 Synergistic effect
The synergistic effect defines as two gases mixing result in nonlinear behaviour along with this
nonlinearity show its effects. The effect can be categorized as [1].
Synergistic with positive effect
Synergistic with negative effect
58
Linear relation synergistic effect
Synergistic effect
Positive synergistic effect referred as whenever two mixed gases result of breakdown
strength (BS) is much superior in worth from individual gases are sum weighted.
Furthermore, when the breakdown strength (BS) result of these two mixed proper gases
is fewer than individual gases are sum weighted, then called by negative synergistic
effect [120]. Equation (6.5) is revealed the relation of index C synergistic effect,
breakdown voltage as well as mixing ratios.
Vm = V2+
k(V1âV2)
k+(1âk)C V1> V2
(6.5)
V1 and V2are represented with breakdown voltages of pure one, Vm denotes clearly breakdown
voltage with proper mixed gases, also C demonstrate the synergistic effect, while k presents the
mixing ratio.
6.7.1 Synergistic effect of R152a /CO2
Using Equation (6.5), the synergistic effect of R152a/CO2 has premeditated as in Table 5.5 and 5.6
correspondingly. Comprehensively investigation of R152a/CO2is given in Table 6.4 accordingly.
The indication of value of C is provided in Table 6.4 below.
When C greater than one, it provided negative- synergistic effect
When C =1, the relation presents the linear effect
When C greater than 0 and less than 1, only synergistic effect
When C less than 0, in this condition called positive synergistic effect
Table 6.4. Synergistic effect of R152a/CO2
Pressures(lb./iđ§đ) K (%)
(0.50) (0.60) (0.70) (0.80)
5 0.18 -0.10 -0.48 -0.86
C
10 0.39 0.41 -0.31 0.42
20 0.08 -0.02 -0.29 -0.60
30 -0.02 0.38 -0.05 -0.70
40 0.07 -0.06 -0.28 -0.66
50 0.28 0.08 -0.26 -0.62
6.8 Insulation Self-Recoverability Test of Gas mixtures
If a fault occurs due to a breakdown that will create a surge and it raised the temperature of these
gases, the blends have the ability to reduce the breakdown surge and restore their original form is
59
entitle insulation self-recovery. This mixture has insulation self-recoverability properties as that of
SF6 gas because CO2 also have arc quenching properties [121-123]. Breakdown tests of AC power
frequency were carried out in testing circuit exposed above chapter 5. Test has been intended for
each one minute, twenty shots for this breakdown was tested to this insulation gas as shown in
figure 6.6. Diminutive quantity of carbon was observed lying on electrodes Although few
drawbacks occurred, that can be eliminated by specific techniques of preventing carbonization
available in literature [124]. By and large, self-recoverability of proposed gases mixture is excellent.
Figure 6.5. Insulation self-recoverability.
6.9 R152a/CO2 Liquefaction Temperature Analysis
In the practical engineering application of new alternate gas, the most important parameter is
liquefaction temperature limitation. R152a liquefaction temperature is â25°C, while that of SF6 is
â64°C [125]. The association of vapor pressure with condensation temperature is revealed in Figure
6.7 for R152a and SF6 revealed lower value of condensation temperature for R152a. Thus, it
becomes necessary to mix R152a with air, CO2, N2 or buffer gases to meet the requirement of low
liquefaction temperature. Liquefaction temperature of pure gases like N2, CO2, air and R152a are
shown in Figure 6.8. CO2 has been preferred over other buffer gases like nitrogen and air due to its
superior arc quenching ability to produce the appropriate mixture for circuit breaker and disconnect
switch applications [126-127]. In this research, R152a was used along with the mixtures of CO2
resulting in reduced depletion of the ozone layer and acceptable liquefaction temperature.
60
Figure 6.6. Saturated vapor pressure R152a and SF6.
Figure 6.7. Liquefaction temperature of pure gases.
The formula for calculating the liquefaction temperature or saturated vapor pressure has been given
in Equation (6.6) [128]. The boiling point (b.p) of R152a is greater than SF6 (â63°C) [129]. Due to
this reason, buffer gas CO2 is added to reduce the disadvantages of high boiling point because CO2
possess very low b.p. Increasing the CO2 content in the mixture of R152a/CO2 reduces overall b.p.
Figure 6.9 shows mixed gas liquefaction temperature. It was proposed that by ever-increasing ratios
of additive gases, the overall liquefaction temperature reduce.
61
Figure 6.8. Liquefaction temperatures of R152aat different pressure and mixture ratio.
These characteristic curves achieved with presumptuous superlative additive gas [130].
P = đŽ[đđ„đ (1â
đđđ
đ )] (6.6)
Gas pressure boiling point is represented with P
Liquefaction temperature denoted by T of R152a in mixture with CO2
Tb atmospheric pressure
R = 2 cal/deg.mol is the gas constant and A = 0 21 cal/deg.molis constant
We have performed simulations in comsolmultiphysics regarding the effect of breakdown in
uniform electric field regarding pure R152a as well as its mixtures in different rations with N2 and
CO2. Simulation results are attached here with which clearly represent that R152a provides better
breakdown field strength with CO2 in comparison to pure R152a as well as its mixture with N2.
Further R152a in combination with CO2 gives better breakdown strength in comparison to SF6 at
the respective gas pressures. For the said analysis, plane to plane gap discharge arrangement was
used as breakdown in uniform field was to be investigated.
62
(a)
(b)
Figure 6.9 Simulation of (a) breakdown voltage, (b) electric filed under different mixtures
The decomposition by-products of the proposed gaseous mixture are analyzed by artificially
decomposed the gaseous mixture. For this purpose, the gaseous mixture was decomposed by
subjecting it to the multiple voltage stresses which cause the repetitive breakdown of the gaseous
mixture under the point-sphere electrode arrangement. It was found that carbon fumes are formed
and deposited on electrodes as shown in Figure 3. Further research is required for the detailed
analysis of decomposition by-products and also attempts should be made to find additives to reduce
the decomposition by-products.
Figure 6.10. Carbon fumes deposited on electrodes.
63
Chapter 07
Conclusion and Future Directions
In this thesis, the main focus was on investigating a good alternative to SF6 which provides
equivalent insulation properties as that of SF6 while also being environment friendly. So, variants of
different mixtures were identified and tested. This work was undertaken to ascertain the potential
significance of R152a gas as an upcoming substitute to sulfur hexafluoride(SF6) in metal gear
equipment of distribution system and other engineering applications. This study specifically focuses
on R252a and CO2 gas mixtures and their significance as insulation medium in high voltage switch
gears.
In this thesis harmful impact on environment has been discussed in detail and how it accumulates in
ozone layer and deteriorates it due to its inert nature. There is great concern over high GWP
provided by SF6 and as its greenhouse gas so it is essential that the manufacturers and industries
start considering substitute for SF6 gas to reduce the effect of global warming. This study discusses
in detail that R152a has low value of GWP and it is less hazardous to environment as compared to
SF6 gas. Leakage of SF6 is one of major issues which is not highlighted because the field emission
of this gas does not match the documented results. The estimated leakage ratio of SF6 in high
voltage switch gear in distribution network is covered in chapter 4 and it is also discussed that how
this issue is often over-looked but it is causing serious damage to environment even if leakage is
considered to be 0.01% on annual basis. The expected leakage of SF6 gas is then compared with
emission of CO2 and it is further discussed how leakage of SF6 gas was not reported because of
non-existent of Kyoto protocol in its early industry usage.
This research emphasizes on dielectric properties of combination of R152a and CO2 as different
mixture with different ratio of both gases and highlights the significance of this mixture as future
replacement for SF6 gas in industrial applications. The mixture of R152a and CO2 is tested
experimentally and its insulation properties are then compared with SF6 gas under different
breakdown voltage levels and lastly, its GWP index is compared with that of SF6 gas and
conclusion is drawn that it is more environment friendly than SF6.
The results from practical experimentation are summarized below:
(1) The gaseous mixture of R152a and CO2 with the ratios as 80% and 20 % respectively shows
more than 90% of insulation characteristics as that of SF6 gas.
64
(2) The breakdown voltage levels in AC system for mixture of R152a/CO2 shows linear relation
with the gap length i.e. if we increase gap length of electrodes the level of breakdown voltage also
increases. The proposed mixture also shows good insulation properties under low temperature
electrical applications.
(3) The proposed mixture is also less hazardous to environment as its contribution to GWP is almost
10% less as compared to SF6.
Constraints in the usage of proposed mixture
As we know that currently heavy investment has been made in current grid station system in
installation of SF6 gas compatible breakers and SF6 gas is being utilized globally so it will be very
difficult to replace it very quickly and even if any alternative provides better results as compared to
SF6 gas the industry will be hesitant to utilize it unless it is proven to provide better results in live
field equipment. So it will be a good solution to first try the mixture out on a small scale and then
gradually increase its consumption rate as its performance is monitored on global scale. Due to its
low GWP and current focus on reducing the greenhouse gases to save depletion of ozone layer it
will be a great kick up start for utilization of this proposed mixture and a quick transition then can
be made possible form SF6 gas to the proposed mixture once its environmental benefits are
documented worldwide. As SF6 gas leakage is now regulated worldwide and so any new alternative
will face a tough challenge to replace it in industrial application.
7.2 Future Work
The future scope should be investigation of this and other mixture at high voltage levels so they can
replace SF6 gas in high voltage equipment. The proposed mixture application is in distribution
switchgears while SF6 gas is being utilized at 500kV rated switch gears. This area is totally open
and has a vast mixture of gases available to test their insulation characteristics and develop a
mixture which is environmentally friendly and provides better insulation properties as compared to
that of SF6 gas.
This area of research has great future potential to develop different alternatives to SF6 gas.
Furthermore, special attention should also be placed to develop a much cheaper and
environmentally friendly insulation medium so it is therefore recommended to keep following
points in mind while doing future research on R152a and its related variants.
Future research should focus on improving insulation characteristics of R152a along with
other gaseous mixture and utilization of such mixtures at high voltage level
65
Any variant of the R152a with different gases along with different utilization ratios should
be tested and compared to know which performs better. For example, we have taken 80/20
percentage ratio of R152a/ CO2respectively. R152a ratio with different gases such as NO2 at
different pressure levels can be tested and compared.
66
References
[1] Climate Change 2007: Working Group I: The Physical Science Basis. Available online:
https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2â10â2.html. Cambridge
University Press, Cambridge, United Kingdom and New York, NY, USA, (accessed on 14th
August 2017).
[2] Environmental News Service. Potent New Greenhouse Gas Discovered. 2000 [cited 2010 26
May 2010]; Available from:
http://www2.fluoridealert.org/Pollution/GreenhouseGases/Potent-New-Greenhouse-Gas-
Discovered.
[3] Hopf, A.; Rossner, M.; Berger, F.; Prucker, U. Dielectric strength of alternative insulation
gases at high pressure in the homogeneous electric field. In Proceedings of the IEEE
Electrical Insulation Conference (EIC), Seattle, WA, USA, 7â10 June 2015
[4] J. D. Mantilla, N. Gariboldi, S. Grob and M. Claessens, "Investigation of the Insulation
Performance of a New Gas Mixture with Extremely Low GWP", IEEE Electr. Insul. Conf.
(EIC), Philadelphia, Pennsylvania, USA, pp. 469-473, 2014..
[5] S. ThĂ©oleyre, âCahier Technique no. 193: MV breaking techniquesâ, Schneider Electric,
2000. [Online]. Available: http://www.schneider-electric.com.
[6] Hideyuki Miyahara, Akitoshi Nakajima, Tatsuya Ishikawa and Satoru Yanabu âInsulating
System to Reduce the Amount of Oilâ, IEEE Transactions on Dielectrics and Electrical
Insulation Vol. 15, No. 2; April 2008.
[7] D. Koch, âSF6 properties, and use in MV and HV switchgear,â Schneider Electric, February
2003. [Online]. Available: http://www.schneider-electric.com..
[8] R. W. Blower, Distribution Switchgear - Construction, performance, selection and
Installation. London: Collins Professional and Technical Books, 1986.
[9] L. Hewitson, M. Brown and B. Ramesh, Practical Power System Proctection, S. Mackay,
Ed., Oxford: Newnes, Elsevier Ltd, IDC Technology, 2005.
[10] P. Duquerroy, G. Sonzogni, G. Perrissin and B. J. Bouillon, âMV Switchgear breaking in
SF6: The Situation after 20 Years in Service,â in Trends in Distribution Switchgear, IEE
Conference Publication No. 400, 1994.
[11] L. T. Falkingham, M. Waldron and Vacuum Interrupters Ltd., âVacuum for HV applications
- Perhaps not so new? - Thirty Yearsâ Service Experience of 132kV Vacuum Circuit
67
breaker,â in International Symposium on Discharges and Electrical Insulation in Vacuum,
ISDEIV '06 (Volume:1 ) , Matsue, 2006
[12] C. T. Dervos and P. Vassiliou, âSulphur Heaxafluoride (SF6): Global Environmental Effects
and Toxic Byproduct Formation,â in Air & Waste Management Association, vol. 50, no.
ISSN 1047-3289, pp. 137-141, 2000
[13] H. Katagiri, H. Kasuya and S. Yanabu, âMeasurement of Iodine Density Generated from
CF3I-CO2 Mixture after Current Interruption,â Presented at Japan-Korea Joint Symposium
on Electrical Discharge and High Voltage Engineering, Shibaura Institute of Technology,
Tokyo, 2007.
[14] H. Katagiri, H. Kasuya, H. Mizoguchi and S. Yanabu, âInvestigation of the Performance of
CF3I Gas as a Possible Substitute for SF6,â in IEEE Transactions on Dielectrics and
Electrical Insulation, Tokyo Denki Univ, vol. 15, Issue 5, pp. 1424 â 1429, 2008.
[15] O. Farish, M. D. Judd, B. F. Hampton and J. S. Pearson, âSF6 insulation systems and their
monitoring,â in Advances in High Voltage Engineering, vol. 40, A. Haddad and D. Warne,
Eds., London, IEE Power & Energy Series 40, The Institute of Electric Engineers, p. 37-76,
2004.
[16] Siemens Energy Sector, âPower Engineering Guide: Switchgear and Substations, 7th
Edition,â 02 08 2012. [Online]. Available:
http://www.energy.siemens.com/us/pool/hq/energy-
topics/power%20engineering%20guide/PEG_70_KAP_03.pdf.
[17] Christophorou, L.G., J.K. Olthoff , R.J. Van Brunt. Sulfur hexafluoride and the electric
power industry. IEEE Electrical Insulation Magazine, 1997. 13(5): p. 20-24.
[18] Takuma T.. âGas Insulation and Greenhouse Effectâ. Journal of The Institute of Electrical
Engineers of Japan, 1999. 119: p. 232-235.
[19] Malik N., A. Qureshi. âBreakdown gradients in SF6-N2, SF6-Air, and SF6-CO2 mixturesâ.
IEEE Transactions on Electrical insulation, 1980(5): p. 413-418.
[20] Malik N., A. Qureshi. âA review of electrical breakdown in mixtures of SF6 and other
gasesâ. IEEE Transactions on Electrical Insulation, 1979(1): p. 1-13.
[21] HernĂĄndez-Ăvila, J. E. Basurto, J. De Urquijo. âElectron transport and swarm parameters in
CO2 and its mixtures with SF6â. Journal of Physics D: Applied Physics, 2002. 35(18): p.
2264.
[22] Pinheiro M., J. Loureiro. âEffective ionization coefficients and electron drift velocities in
gas mixtures of SF6 with He, Xe, CO2, and N2 from Boltzmann analysisâ. Journal of
Physics D: Applied Physics, 2002. 35(23): p. 3077.
68
[23] Christophorou L G, Olthoff J K, and Green D S. âGases for electrical insulation and arc
interruption: possible present and future alternatives to pure SF6â. NIST Technical Note
1425. (Washington DC: National Institute of Standards and Technology), 1997
[24] United Nations Framework Convention on Climate Changes (UNFCCC). âKyoto protocol
to the united nations framework convention on climate changesâ. 1997. url:
http://unfccc.int/kyoto_protocol/items/2830.php
[25] De Urquijo, J. E. Basurto, J. âHernĂĄndez-Ăvila. Measurement of electron drift, diffusion,
and effective ionization coefficients in the SF6âCHF3 and SF6âCF4 gas mixturesâ. Journal
of Physics D: Applied Physics, 2003. 36(24): p. 3132.
[26] De Urquijo, J. E. Basurto, J. âHernĂĄndez-Ăvila. Measurement of electron drift, diffusion,
and effective ionization coefficients in the SF6âCHF3 and SF6âCF4 gas mixturesâ. Journal
of Physics D: Applied Physics, 2003. 36(24): p. 3132.
[27] Fang, X. et al.. âSulfur hexafluoride (SF6) emission estimates for China. an inventory for
1990â2010 and a projection to 2020â. Environmental science & technology, 2013. 47(8): p.
3848-3855.
[28] Zhang, Ge, ChangjunKe, and Shujuan Zhang. "Diffuse volume-discharges without pre-
ionization formed in SF6 and C2H6 mixtures." Journal of Electronics (China) 31.3 (2014):
267-270.
[29] TadahiroY.. âThe Development and practical use of a new 24kV dry air-insulated
switchgearâ. Mitsubishi, 1986. 10.
[30] Rokunohe, T. et al. âFundamental insulation characteristics of air; N2, CO2, N2/O2, and
SF6/N2 mixed gasesâ. Electrical Engineering in Japan, 2006. 155(3): p. 9-17.
[31] Rokunohe, T. et al. âFundamental insulation characteristics of air, N2, CO2, N2/O2 and
SF6/N2 mixed gasesâ. IEEJ Transactions on Power and Energy, 2005. 125: p. 619-625.
[32] Chen, L. et al. âBreakdown characteristics of CF3I/CO2 gas mixtures under fast impulse in
rod-plane and GIS geometriesâ. in 19th International Symposium on High Voltage
Engineering. 2015.
[33] Ngoc M.N. et al. âElectrical breakdown of CF 3 I and CF3I-N2 gas mixtures. in Electrical
Insulation and Dielectric Phenomenaâ. CEIDP'09. IEEE Conference on. 2009. IEEE.
[34] Kamarudin, M. et al. âA survey on the potential of CF 3 I gas as an alternative for SF 6 in
high voltage applicationsâ. in Universities Power Engineering Conference (UPEC), 2010
45th International. 2010. IEEE.
69
[35] Widger P, A. Haddad, H. Griffiths. âBreakdown performance of vacuum circuit breakers
using alternative CF 3 I-CO 2 insulation gas mixtureâ. IEEE Transactions on Dielectrics
and Electrical Insulation, 2016. 23(1): p. 14-21.
[36] Hunter S., L. Christophorou. âPressureâdependent electron attachment and breakdown
strengths of unary gases and synergism of binary gas mixtures: A relationshipâ. Journal of
applied physics, 1985. 57(9): p. 4377-4385.
[37] Mantilla, J. et al. âInvestigation of the insulation performance of a new gas mixture with
extremely low GWPâ. in Electrical Insulation Conference (EIC), 2014. 2014. IEEE.
[38] Hyrenbach M., S. Zache. âAlternative insulation gas for medium-voltage switchgearâ. in
Petroleum and Chemical Industry Conference Europe (PCIC Europe), 2016. 2016. IEEE.
[39] SchneiderElectric,"Cashiertechniqueno.193MVbreakingtechniques,"1999.
[40] A.H.CooksonandB.O. Pedersen, "Analysis of the HV breakdown results for mixture of
SF6 with CO2, N2 and Air," in 34th International Symposium on High Voltage
Engineering1979.
[41] Hitoshi Sato, Keiichi Morita, et al., "A fundamental study on electrical insulation of
N2/SF6 gas-insulated electric power apparatus," Electrical Engineering in Japan, Vol. 139,
pp. 9-16,2002.
[42] H. J. Lingal, A. P. Strom, et al., "An Investigation of the Arc -Quenching Behavior of
Sulfur Hexafloride," Power Apparatus and Systems, Part III. Tran sactionsof the American
Institute of Electrical Engineers, Vol. 72, pp. 242 -246, 1953.
[43] L.J.Cao and A.D.Stokes, "Ablation arc: Time constants of ablation -stabilized arcs in PTFE
and ice," pp. 1557-1562, 1991.
[44] Sweden NynasNaphthenics Ab, "Base Oil Handbook," 2001.
[45] I.Cotton and M. Barnes, "Options for the replacement of sulphur hexafluoride gas in the
transmission system."
[46] Toshiba, "72.5 to 1100kV High Voltage Gas Insulated Switchgear Brochure."
[47] M S Naidu and V Kamaraju, "Chapter 3 Conduction and breakdown in liquid dielectrics," in
High voltage Engineering 2nd Edition: McGraw -Hill, 1996.
[48] K.S.Kao, "Some electromechanical effects on liquid dielectrics," Br.J.Appl.Phys., Vol. 12,
pp. 141-148, 1961
[49] www.midel.com, 25th October 2007
[50] Y. Pelenc, "Review of current interruption techniques," Power systems engineering data,
Vol. 1, No.2, January, 1979.
[51] "C.P.S. Envorotemp FR3 Datasheet 900-20."
70
[52] Q. Liu, Z.D. Wang, et al., "Impulse breakdown voltages of ester-based transformer oils
determined by using different test methods," IEEE Conference on Electrical Insulation and
Dielectric Phenomena, pp. 608 -612, 18-21 Oct. 2009.a
[53] J. d. Urquijo, âIs CF3I a good gaseous dielectric? A comparative swarm study of CF3I and
SF6,â in 5th EU-Japan Joint Symposium on Plasma Processing, Instituto de CienciasFisicas,
Universidad Nacional Autonoma de Mexico, Journal of Physics: Conference series 86, Issue
1, pp. 012008, 2007.
[54] H. Toyota, S. Nakauchi, S. Matsuoka and K. Hidaka, âVoltage-time Charactersitics in SF6
and CF3I Gas within Non-uniform Electric Field,â in Proceedings of the XIVth International
Symposium on High Voltage Engineering, Beijing, China, Paper H-04, pp. 1-6, 2005.
[55] United Nations Framework Convention on Climate Change (UNFCCC), âKyoto Protocol,â
UNFCC, 2008. [Online]. Available: http://unfccc.int/kyoto_protocol/items/3145.php.
[56] Intergovernmental Panel on Climate Change (IPCC), Working Group I Contribution to
Fourth Assessment Report of the IPCC - Intergovernmental Panel on Climate Change,
Geneva, Switzerland: Addendum-Errata of Climate Change 2007 - The Physical Science
Basis IPCC WG1 AR4 Report, 2008.
[57] United States Environmental Protection Agency (EPA), âEPA Overview of Greenhouse
Gases,â 09 09 2013. [Online].
Available:http://epa.gov/climatechange/ghgemissions/gases/fgases.ht
[58] D. J. Jacob, âIntroduction to Atmospheric Chemistryâ, Harvard: Princeton University Press,
1999. [Online]. Available: http://www-as.harvard.edu/people/faculty/djj/book/.html.
[Accessed 01 02 2014].ml.
[59] J. A. Patz and J. J. West, ââThe Paris agreement could saves lives in China,ââ Lancet
Planetary Health, vol. 2, no. 4, pp. e147âe148,
[60] X. Zhang et al., ââReactive molecular dynamics study of the decomposition mechanism of
the environmentally friendly insulating medium C3F7CN,ââ RSC Adv., vol. 7, no. 80, pp.
50663â50671, 2017.
[61] J. Xiong, X. Li, J. Wu, X. Guo, and H. Zhao, ââCalculations of total electron-impact
ionization cross sections for fluoroketone C5F10O and fluoronitrile C4F7N using modified
DeutschâMĂ€rk formula,ââ J. Phys. D, Appl. Phys., vol. 50, no. 44, pp. 445206â445212,
2017.
[62] Y. Kieffel, F. Biquez, P. Ponchon, and T. Irwin, ââSF6 alternative develop- ment for high
voltage switchgears,ââ in Proc. IEEE Power Energy Soc. Gen. Meeting, Jul. 2015, pp. 1â5.
71
[63] Y. Wu et al., ââProperties of C4F7N-CO2 thermal plasmas: Thermodynamic properties,
transport coefficients and emission coefficients,ââ J. Phys. D, Appl. Phys., vol. 51, no. 15,
pp. 155206â155217, 2018.
[64] X. Li, H. Zhao, and A. B. Murphy, ââSF6-alternative gases for application in gas-insulated
switchgear,ââ J. Phys. D, Appl. Phys., vol. 51, no. 15, pp. 153001â153019, 2018.
[65] H. Zhao, X. Li, N. Tang, X. Jiang, Z. Guo, and H. Lin, ââDielectric proper- ties of
fluoronitriles/CO2 and SF6/N2 mixtures as a possible SF6-substitute gas,ââ IEEE Trans.
Dielectr. Electr. Insul., vol. 25, no. 4, pp. 1332â1339, Aug. 2018.
[66] B. Zhang, N. Uzelac, and Y. Cao, ââFluoronitrile/CO2 mixture as an eco- friendly alternative
to SF6 for medium voltage switchgears,ââ IEEE Trans. Dielectr. Electr. Insul., vol. 25, no. 4,
pp. 1340â1350, Aug. 2018.
[67] Y. Tu, Y. Cheng, C. Wang, X.Ai, F.Zhou, and G. Chen, ââInsula- tion characteristics of
fluoronitriles/CO2 gas mixture under DC electric field,ââ IEEE Trans. Dielectr. Electr.
Insul., vol. 25, no. 4, pp. 1324â1331, Aug. 2018.
[68] C. Wang et al., ââCharacteristics of C3F7CN/CO2 as an alternative to SF6 in HVDC-GIL
systems,ââ IEEE Trans. Dielectr. Electr. Insul., vol. 25, no. 4, pp. 1351â1356, Aug. 2018.
[69] H. E. Nechml, A. Beroual, A. Girodet, and P. Vinson, ââEffective ion- ization coefficients
and limiting field strength of fluoronitriles-CO2 mix- tures,ââ IEEE Trans. Dielectr. Electr.
Insul., vol. 24, no. 2, pp. 886â892, Apr. 2017.
[70] H. E. Nechmi, A. Beroual, A. Girodet, and P. Vinson, ââFluoronitriles/CO2 gas mixture as
promising substitute to SF6 for insulation in high volt- age applications,ââ IEEE Trans.
Dielectr. Electr. Insul., vol. 23, no. 5, pp. 2587â2593, Oct. 2016.
[71] A. Hopf, J. A. Britton, M. Rossner, and F. Berger, ââDielectric strength of SF6 substitutes,
alternative insulation gases and PFC-gas-mixtures,ââ in Proc. IEEE Electr. Insul. Conf.
(EIC), Jun. 2017, pp. 209â212.
[72] J. G. Owens, ââGreenhouse gas emission reductions through use of a sustainable alternative
to SF6,ââ in Proc. 34th Electr. Insul. Conf. (EIC), Jun. 2016, pp. 535â538.
[73] C. Preve, R. Maladen, and D. Piccoz, ââMethod for validation of new eco- friendly
insulating gases for medium voltage equipment,ââ in Proc. IEEE Int. Conf. Dielectr. (ICD),
vol. 1, Jun. 2016, pp. 235â240.
[74] Y. Deng, Y. Ma, X. Chen, S. Zhang, and X. Chen, ââAC breakdown charac- teristics of
CF3I-N2 gas mixtures in condition of quasi-homogeneous and extremely non-uniform
electric field,ââ High Voltage Eng., vol. 43, no. 3, pp. 754â764, 2017.
72
[75] Y. Li et al., ââStudy on the dielectric properties of C4F7N/N2 mixture under highly non-
uniform electric field,ââ IEEE Access, vol. 6, pp. 42868â42876, 2018.
[76] Z. Zhao, High Voltage Technology, 2nd ed. Beijing, China: China Electric Power Press,
2006.
[77] C. Guo et al., ââInfluence of electric field non-uniformity on breakdown characteristics in
SF6/N2 gas mixtures under lightning impulse,ââ IEEE Trans. Dielectr. Electr. Insul., vol. 24,
no. 4, pp. 2248â2258, Sep. 2017.
[78] Y. Qiu, J. Che, and M. Zhang, ââThe homogeneity of SF6 gas mixture in under high drop
condition,ââ High Voltage Appl., vol. 25, no. 3, pp. 12â16, 1989.
[79] J. Zhang, T. Xia, and S. Lai, ââStudy on the insulation performance of SF6/N2 mixed
gas in GIL,ââ High Voltage Appl., vol. 52, no. 12, pp. 156â163, 2016.
[80] Wikipedia. (2018). Kinetic Theory of Gases. [Online]. Available: https://
en.wikipedia.org/wiki/Kinetic_theory_of_gases
[81] D. W. Fahey, âTwenty questions and aswers about the ozone layer: 2006 update,â Presented
at Panel Review Meeting for the 2006 Ozone Assessment, Les Diablerets, Switzerland,
2006.
[82] N. M. Nguyen, A. Denat, N. Bonifaci, O. Lesaint and M. Hassanzadeh, âImpulse Partial
Discharges and Breakdown of CF3I in Highly Non-Uniform Field,â Eighteenth International
Conference on Gas Discharges and Their Applications, Ernst-Moritz-Arndt-University,
Greifswald, Germany, pp. 330-3
[83] Widger, P.; Haddad, A.M. Evaluation of SF6 Leakage from Gas Insulated Equipment on
Electricity Networks in Great Britain. Energies 2018, 11, 2037
[84] R. H. Petrucci, W. S. Harwood and F. G. Herring, General Chemistry Principles and Modern
Applications (8th Edition), Eighth Edition, Upper Saddle River, New Jersey, New Jersey:
Prentice-Hall Inc., ISBN 0-13-014329-4, 2002.
[85] P. Atkins and L. Jones, Chemistry Molecules, Matter, and Change, Third Edition, New
York: W. H. Freeman and Company, ISBN 0-7167-2832-X, 1997.33, 2010.
[86] Javadi, H., M. Farzaneh, and A. Peyda. "Determination of electric field at inception based
upon current-voltage characteristics of AC corona in rod-plane gaps." Iranian Journal of
Electrical & Electronic Engineering 6.2 (2010): 119.
[87] Warsito, Agung, Abdul Syakur, and GaluhSusilowati. "An Ozone Reactor Design with
Various Electrod Configurations." International Journal of Electrical and Computer
Engineering 1.2 (2011): 93.
73
[88] Shin, W. J., et al. "Evaluation of uniform and non-uniform breakdown characteristics of
liquid nitrogen with different electrode materials." IEEE Transactions on Applied
Superconductivity 22.3 (2012): 7701404-7701404.
[89] Seela-or, Surapong, et al. "Solid investigation in oil barrier dielectric under non-uniform
electric field." Electrical Engineering/Electronics, Computer, Telecommunications and
Information Technology (ECTI-CON), 2013 10th International Conference on. IEEE, 2013.
[90] Wadhwa, C. L. High voltage engineering. New Age International, 2007.
[91] Okabe S, Wada J, Ueta G. âDielectric properties of gas mixtures with C 3 F 8/C 2 F 6 and N
2/CO 2â. IEEE Transactions on Dielectrics and Electrical Insulation. 2015 Aug;22(4):2108-
16.
[92] Wada J, Ueta G, Okabe S, Hikita M. âDielectric properties of gas mixtures with per-
fluorocarbon gas and gas with low liquefaction temperatureâ. IEEE Transactions on
Dielectrics and Electrical Insulation. 2016 Apr;23(2):838-47.
[93] Xiao; S.; et al.: âAC breakdown characteristics of CF 3 I/N 2 in a non-uniform electric
fieldâ. IEEE Transactions on Dielectrics and Electrical Insulation, 2016. 23(5): p. 2649-
2656.
[94] Zhao H, Li X, Lin H. âInsulation Characteristics of cC4 F8-N2 and CF3/N 2 Mixtures as
Possible Substitutes for SF6. IEEE Transactions on Power Delivery. 2017 Feb;32(1):254-62
[95] Kieffel, Y. A. Girodet, J. Porte. âMedium-or high-voltage electrical appliance having a low
environmental impact and hybrid insulationâ. 2013, Google Patents.
[96] Xiao, S. et al. âAC breakdown characteristics of CF 3 I/N 2 in a non-uniform electric fieldâ.
IEEE Transactions on Dielectrics and Electrical Insulation, 2016. 23(5): p. 2649-2656.
[97] Eiseman Jr Bernhardt J. âMethod and apparatus for preventing carbon deposits in electrical
apparatus containing electronegatively substituted dielectric fluidsâ. 1965, Google Patents.
[98] Kasuya, H., et al. âInterruption capability and decomposed gas density of CF 3 I as a
substitute for SF 6 gasâ.IEEE Transactions on Dielectrics and Electrical Insulation, 2010.
17(4).
[99] Ullah, R.; Ullah, Z.; Haider, A.; Amin, S.; Khan, F. Dielectric properties of
tetrafluoroethane (R134) gas and its mixtures with N2 and air as a sustainable alternative to
SF 6 in high voltage applications. Electr. Power Syst. Res.2018, 163, 532â537.
[100] Ullah, R.; Rashid, A.; Rashid, A.; Khan, F.; Ali, A. Dielectric characteristic of
dichlorodifluoromethane (CCL2F2) gas and mixture with N2/air as an alternative to SF6
gas. High Volt.2017, 2, 205â210.
74
[101] Ray, E.A.; Moore, F.L.; Elkins, J.W.; Rosenlof, K.H.; Laube, J.C.; Röckmann, T.; Marsh,
D.R.; Andrews, A.E.Quantification of the SF6 lifetime based on mesospheric loss measured
in the stratospheric polar vortex.J. Geophys. Res. Atmos.2017, 122, 4626â4638.
[102] Katagiri, H.; Kasuya, H.; Mizoguchi, H.; Yanabu, S. Investigation of the performance of
CF3I Gas as a Possible Substitute for SF6. IEEE Trans. Dielectr. Electr. Insul.2008, 15,
1424â1429.
[103] Zhang, X.; Xiao, S.; Han, Y.; Cressault, Y. Experimental studies on power frequency
breakdown voltage of CF3I/N2 mixed gas under different electric fields. Appl. Phys.
Lett.2016, 108, 092901.
[104] Xiao, S.; Zhang, X.; Han, Y.; Dai, Q. AC breakdown characteristics of CF 3 I/N 2 in a non-
uniform electric field. IEEE Trans. Dielectr. Electr. Insul.2016, 23, 2649â2656.
[105] Zhao, S.; Xiao, D.; Zhang, H.; Deng, Y. Discharge characteristics of CF3I/N2 mixtures
under lightning impulse and alternating voltage. IEEE Trans. Dielectr. Electr. Insul.2017,
24, 2731â2737.
[106] Chen, L.; Widger, P.; Kamarudin, M.S.; Griffiths, H.; Haddad, A. CF3I Gas Mixtures:
Breakdown Characteristics and Potential for Electrical Insulation. IEEE Trans. Power
Deliv.2017, 32, 1089â1097, doi:10.1109/TPWRD.2016.2602259.
[107] Zhang, X.; Li, Y.; Tian, S.; Xiao, S.; Chen, D.; Tang, J.; Zhuo, R. Decomposition
mechanism of the C5-PFK/CO2 gas mixture as an alternative gas for SF6. Chem. Eng.
J.2017, 336, 38â46.
[108] Zhong, L.; Rong, M.;Wang, X.; Wu, J.; Han, G.; Han, G.; Lu, Y.; Wu, Y. Compositions,
thermodynamic properties, and transport coefficients of high temperature C5F10O mixed
with CO2 and O2 as substitutes for SF6 to reduce global warming potential. AIP Adv.2017,
7, 075003.
[109] Zhang, X.; Tian, S.; Xiao, S.; Deng, Z.; Li, Y.; Tang, J. Insulation Strength and
Decomposition Characteristics of a C6F12O and N2 Gas Mixture. Energies2017, 10, 1170.
[110] Wang, C.; Cheng, Y.; Tu, Y.; Chen, G.; Yuan, Z.; Xiao, A.; Owens, J.; Zhang, A.; Mi, N.
Characteristics of C3F7CN/CO2 as an alternative to SF6 in HVDC-GIL systems. IEEE
Trans. Dielectr. Electr. Insul. 2018, 25, 1351â1356.
[111] Zhang, X.; Chen, Q.; Zhang, J.; Li, Y.; Xiao, S.; Zhuo, R.; Tang, J. Experimental Study on
Power Frequency Breakdown Characteristics of C4F7N/CO2 Gas Mixture Under Quasi-
Homogeneous Electric Field. IEEE Access2019, 7, 19100â19108.
75
[112] International Electrotechnical Commission. High-Voltage Switchgear and Controlgear-Part
1: Common Specifications for Alternating Current Switchgear and Control Gear; IEC
62271-1; International Electrotechnical Commission: London, UK, 2007; p. 252.
[113] Koch, D. SF6 Properties, and Use in MV and HV Switchgear; Cahier Techique No. 188;
Schneider Electric: Rueil-Malmaison, France, 2003.
[114] Okabe, S.; Wada, J.; Ueta, G. Dielectric properties of gas mixtures with C3F8/C2F6 and
N2/CO2. IEEE Trans. Dielectr. Electr. Insul.2015, 22, 2108â2116.
[115] Zhao, S.; Xiao, D.; Xue, P.; Zhong, R.; Deng, Y. Experimental research on polarity effect of
CF3I/N2 mixtures under lightning impulse. IEEE Trans. Dielectr. Electr. Insul.2018, 25,
1357â1363.
[116] Zhang, B.; Uzelac, N.; Cao, Y. Fluoronitrile/CO2 mixture as an eco-friendly alternative to
SF6 for medium voltage switchgears. IEEE Trans. Dielectr. Electr. Insul. 2018, 25, 1340â
1350.
[117] Nechml, H.E.; Beroual, A.; Girodet, A.; Vinson, P. Effective ionization coefficients and
limiting eld strength of fluoronitriles-CO2 mixtures. IEEE Trans. Dielectr. Electr. Insul.
2017, 24, 886â892.
[118] Xiao, D. Insulating Characteristics of Potential Alternatives to Pure SF6. In Gas Discharge
and Gas Insulation; Springer: Heidelberg, Germany, 2016; pp. 271â309.
[119] Li, X.; Zhao, H.; Murphy, A.B. SF6-alternative gases for application in gas-insulated
switchgear. J. Phys. D Appl. Phys.2018, 51, 153001â153009.
[120] KovĂĄcs, T.; Feng, W.; Totterdill, A.; Plane, J.M.C.; Dhomse, S.; GĂłmez-MartĂn, J.C.;
Stiller, G.P.; Haenel, F.J.; Smith, C.; Forster, P.M.; et al. Determination of the atmospheric
lifetime and global warming potential of sulfur hexafluoride using a three-dimensional
model. Atmos. Chem. Phys. Discuss.2017, 17, 883â898.
[121] Hösl, A.; Pachin, J.; EgĂŒz, E.; Chachereau, A.; Franck, C. Positive synergy of SF6 and
HFO1234ze(E). IEEE Trans. Dielectr. Electr. Insul.2019, doi:10.3929/ethz-b-000353101.
[122] International Electrotechnical Commission (IEC). High-Voltage Test TechniquesâPartial
Discharge Measurements; IEC-60270; IEC: London, UK, 2000.
[123] Widger, P.; Griffiths, H.; Haddad, A. Insulation strength of CF3I-CO2 gas mixtures as an
alternative to SF6 in MV switch disconnectors. IEEE Trans. Dielectr. Electr. Insul.2018, 25,
330â338.
[124] Kasuya, H.; Kawamura, Y.; Mizoguchi, H.; Nakamura, Y.; Yanabu, S.; Nagasaki, N.
Interruption capability and decomposed gas density of CF3I as a substitute for SF6 gas.
IEEE Trans. Dielectr. Electr. Insul.2010, 17, 1196â1203.
76
[125] Ohtsuka, S.; Nagara, S.; Miura, K.; Nakamura, M.; Hikita, M. Effect of Mixture of a Small
Amountof CO2 in SF6/N2 mixed gas on the insulation Performance under Nonuniform
Field. In Proceedings of the 2000 IEEE International Symposium on Electrical Insulation,
Anaheim, CA, USA, 5 April 2000; pp. 288â291.
[126] Widger, P.; Haddad, A. Evaluation of SF6 Leakage from Gas Insulated Equipment on
Electricity Networks in Great Britain. Energies2018, 11, 2037.
[127] Su, Z.; Dengming, X.; Peng, X.; Ruishuang, Z.; Yunkun, D. Analysis of insulation
performance and polar effect of CF3I/CO2 mixtures. IEEE Trans. Dielectr. Electr.
Insul.2018, 25, 1364â1370, doi:10.1109/TDEI.2018.007117.
[128] Kharal,H.S Muhammad Kamran, Sohail Aftab Qureshi Safeguard Guide for Recycling and
Handling the Alternative of SF6 GAS in Electrical Investigatory Applications World
Scientific News 95 (2018) 182-192.
[129] Kharal, H. S., Ullah, R., Ullah, Z., Asghar, R., Uddin, W., Azeem, B., ... & Kamran, M.
(2018, September). Insulation Characteristic of CCl 2 F 2 with mixtures of CO 2/N as a
Possible Alternative to SF 6 substitute Gas for High Voltage Equipmentâs. In 2018
International Conference on Power Generation Systems and Renewable Energy
Technologies (PGSRET) pp. 1-5.
[130] Kharal, H.S.; Kamran, M.; Ullah, R.; Saleem, M.Z.; Alvi, M.J. Environment-Friendly and
Efficient Gaseous Insulator as a Potential Alternative to SF6. Processes 2019, 7, 740.
77
Appendices
Appendix A
A-1 Different alternative of SF6 gas. The global warming potential represents
the values over a time span of 100 years for equal masses of these gases.
Reference Gas
Dielectric
Strength
(DS)
Global
Warming
Potential
Atmosphere
Lifetime
Boiling
Point Cost/kg
[11] SF6 1 22,800 3200 â63â 25â30 $
[21] N2 0.40 0 â195.8â 0.25 times of
SF6
[22] CO2 0.37 1 â78.5â 0.35 times of
SF6
[22] C2F6 0.80 12,200 10,000 â78.1â 2.5 times of SF6
[22] C3F8 0.90 8830 2600 â36.7â 2 times of SF6
[22] CF3I 1.21 5 0.05 â22.5â 10 times of SF6
[22] C4F10 1.2â1.3 8700 3200 â5.99â 9 times of
SF6
A-2 Characteristics of SF6 Verses R152a
Properties Sulfur Hexafluoride Difluoroethane
Molecular formula SF6 CF2HCH3
Molecular weight 146.06 g/mol 66.05 gmol1
GWP 23900 140
Appearance Colorless Colorless
Density 6.17 kg/mÂł 0.90g/ccat 25 deg.C(77
deg,F).liquid
Melting point -50.8 C -117âŠC/-179âŠF
Boiling point -64 °C -25âŠC (-13âŠF)
Solubility in water 0.003% (25 °C) 0.28WT%@25C(77F)(87Pasia)
Vapour Density(air=0) 2.5 2.42
Electronegativity Not Applicable
Vapor pressure 10.62 bar 87 pasia@25âŠC (77âŠF )
Flash Point None
Atmospheric life 3200 1.5
Molecular mass 146.06 g/mol 66.1 g/mol
Price/kg $28 to $30 $12
78
A-3 Association of SF6 replacement
Gases Problems and Drawbacks
Carbon dioxide, Nitrogen and Dry air
Momentous expansion in pressure.
Momentous expansion in size of equipment.
Low breakdown voltage [17].
Trifluoro iodomethane mixtures
(CF3I/CO2 or N2)
Boiling point large than that of CF3I (â22.5 °C) at 0.1 MPa.
Classified as a perilous, mutagenic, and venomous for
facsimile (Type-3) [18].
Mixtures of per-fluorinated ketones
(C5F10O, C6F12O/Technical air or
CO2)
Superior smallest operating temperature than SF6 [19]. Far
above the ground boiling temperature (24°C) at (0.1 MPa)
because of higher molecular mass.
HFO 1234ze
Carbon grime dump on electrodes owing to high spark
voltage. Superior operating temperature than SF6 while
unpolluted (constrained at â15 °C).
C4F7N/CO2 Having high boiling point (â4.7 °C at 0.1 MPa) [14]
79
Appendix B
Worldwide usage and leakage of SF6 from all RMUâs [33]
Worldwide
SF6
insulated
RMUâs
Expected
SF6 Mass of
each
component
Total SF6
used in all
RMUâs
Annually
leakageof
SF6 from all
RMUâs
Cumulative
25 years
leakage of
SF6 from all
RMUâs
2,322,600 0.6 kg 1,393,560 kg 1,376 kg 34,424 kg
Worldwide usage and leakage of SF6 from all CBâs [83]
Worldwide
SF6
insulated
CBâs
Expected SF6
Mass of each
component
Total SF6
used in all
CBâs
Annually
leakageofSF6
from all CBâs
Cumulative
25 years
leakage of
SF6 from all
CBâs
500,000 0.3 kg 150,000 kg 148 kg 3705 kg
Worldwide usage and leakage of SF6 from all switches [83].
Worldwide
SF6insulated
Switches
Expected SF6
Mass of each
component
Total SF6
used in all
Switches
Annually
leakageofSF6
from all
Switches
Cumulative 25
years leakage of
SF6 from all
Switches
677,400 0.429 kg 290,604 kg 287 kg 7178 kg
80
Total amount of SF6 use in all RMUâs, CBâs and switches [83]
Worldwid
e SF6
insulated
RMUâs
Worldwide
SF6insulate
d CBâs
Worldwide
SF6insulate
d Switches
Total
SF6 used
in all
MV
RMUâs,
CBâs &
Switches
Annually
leakageofSF
6 from
allMV
RMUâs,
CBâs &
Switches
Cumulativ
e 25 years
leakage of
SF6 from
all MV
RMUâs,
CBâs &
Switches
2,322,600 500,000 677,400 1,834,16
4 kg
1,812 kg 45,308 kg
Worldwide usage and leakage of SF6 from all GIS [83]
Worldwide
SF6insulated
GIS
Expected
SF6 Mass of
each
component
Total SF6
used in all
GIS
Annually
leakageofSF6
from all GIS
Cumulative 25
years leakage of
SF6 from all GIS
20,000 500 kg 10000000 kg 9881 kg 247023 kg
f) Worldwide usage and leakage of SF6 from all GIL [83]
Worldwide
SF6insulated
GIL
Expected
SF6 Mass of
each km
Total SF6
used in all
GIL
Annually
leakageofSF6
from allGIL
Cumulative 25
years leakage of
SF6 from all GIL
30,000 km 30.24 kg 907184 kg 896 kg 22410 kg
81
Appendix C
C-1 Laboratory Test Setup and Assembly of Test Electrodes
Experimental set up to examine R152a/CO2 breakdown voltage by sphereâsphere electrodes.
(a)
(b)
Test equipment used: (a) Control and measurement unit; (b) Testing vessel (HV-9134); (c)
Experimental setup for DC; (d) Spark formation comparison
Control Desk
Resistor
Measuringcapacitor
Testing Transformer
Connecting Rod
Gas cylinder
Sphere electrode
82
Test setup specification.
Specifications Standards
Voltage (AC) 100 kilovolts
Pressure (p) 0 to 6 bars
Diameter of sphere electrodes 50 mm
Vertical height 800 mm
Experimental constraints
Configuration of Electrodes SphereâSphere
Length of spark gap 6mmâ18mm
AC voltage 0â100 kV (AC)
DC voltage 0â140 kV (DC)
Material of electrode Aluminum Ni plated steel
Different mixture ratio of R152a and CO2
Measurement No. R152a Ratio (%) CO2 Ratio (%)
1 90 10
2 80 20
3 70 30
4 60 40
5 50 50
83
Appendix D
D-1 Calculation of Accurate Gas Mixture Pressure
V = mRTMW Ă Pâ
where:
m = Mass of gas (grams), T = Temperature (Kelvin), P = Pressure (bar);
MW = Molecular weight of gas (g/mol), R = Ideal gas constant, V = Volume (liters).
For example, in R152a operation, the filling temperature was 20°C. The ideal gas constant
(R) is 0.0821, the MW of R152a is 66.01 g/mol and MW of CO2 = 44.01 g/mol. Therefore,
when the chamber is filled with mixture the volume of each gas can be calculated as follows
[27]:
a) Mixture Ratio Analysis
dN = N (α â η) dx
where N refers to initial electron quantity, dN denotes the no of electron traveled a distance
dx.
D-2 Gap Difference Analysis
E = f Ă (V/D)
where constant f is demonstrating non-uniformity, V is applied voltage and D is the distance
between two electrodes.
b) Statistical analysis of R152a.
Base Gas R152a Mixed Gas CO2
RBG1 50% 60% 70% 80% 90%
SD 11.2 12.3 10.21 14.2 12.9
Î 46.1 51.6 59.7 57.3 55.3
Cv 0.23 6 0.27 0.28 0.19
Max kV 60 69.8 73 76.1 71.6
Min kV 26 4 49.8 43 35.6
1RBG: Ratio of base gas; SD: standard deviation; M: mean; cv: coefficient of
variation.
84
D-3 Global Warming Potential (GWP)Analysis
GWP =đĂđđĂđđđ+(đâđ)ĂđđĂđ
đĂđđ+(đâđ)Ăđđ
D-4 Synergistic effect
đđŠ= đđ+
đ€(đđâđđ)
đ€+(đâđ€)đđđ>đđ
V1 and V2 denoted by breakdown voltages of pure one, Vm is the breakdown voltage of
mixed gas, c shows thesynergistic effect and mixing ratios shows by k.
If C is greater than one, it gives negative synergistic effect
If C is equal to one, then it gives linear relation effect
If C is greater than 0 and less than one, it gives synergistic effect
If C is less than 0, it gives positive synergistic effect
Synergistic effect C of R152/co2
Pressure (lb./iđ§đ) K (%)
0.50 0.60 0.70 0.80
5 0.18 -0.10 -0.48 -0.86
C
10 0.39 0.41 -0.31 0.42
20 0.08 -0.02 -0.29 -0.60
30 -0.02 0.38 -0.05 -0.70
40 0.07 -0.06 -0.28 -0.66
50 0.28 0.08 -0.26 -0.62
D-5 R152a/CO2 Liquefaction Temperature Analysis
P = exp[A(1â
đđđ
đ )]
c) where P represents the gas boiling point pressure; T is the liquefaction temperature of
R152a in mixture with CO2; Tb is the liquefaction temperature (K) at atmospheric
pressure;R = 2 cal/deg.mol is the gas constant and A = 21 cal/deg.molis constant.
85
Appendix E
E-1Papers published during work on this project
Hafiz Shafqat Kharal, Muhammad Kamran, Rehmat Ullah, âEnvironment-Friendly
and Efficient Gaseous Insulator as a potential alternative to SF6â, Processes,2019,
7(10), 740. (Thomson Reuters Impact Factor = 1.963)
Muhammad Junaid Alvi, Hafiz Shafqat Kharal, âField Optimization and
Electrostatic Stress Reduction of Proposed Conductor Scheme for Pliable Gas-
Insulated Transmission Linesâ, Applied Sciences, 2019, 9(15), 2988. (Thomson
Reuters Impact Factor = 2.316)
Hafiz Shafqat Kharal, Muhammad Kamran, Rehmat Ullah,
âDichlorodifluoromethane gas mixtures: A Novel Competent Gaseous Insulator as
surrogate of SF6 for Electrical applications", Accepted to International Journal of
Global Warming, 2019(Thomson Reuters Impact Factor = 0.78)
H. Shafqat Kharal, Muhammad Kamran, Sohail Aftab Qureshi, M. Zaheer Saleem,
âSafeguard Guide for Recycling and Handling the Alternative of SF6 Gas in Electrical
Investigatory Applicationsâ, World Scientific News,2018, 95, 182-192.
H. Shafqat Kharal, RehmatUllah, Z. Ullah ; R. Asghar ; Waqar Uddin ; B. Azeem ;
S. M. Ali ; A. Haider, Muhammad Kamran, âInsulation Characteristic of R12(CCl2F2)
with mixtures of CO2/N as a Possible Alternative to SF6substitute Gas for High
Voltage Equipmentâsâ,2018 International Conference on Power Generation Systems
and Renewable Energy Technologies (PGSRET), Islamabad, Pakistan, 2018, pp. 1-5
Muhammad Kamran H. Shafqat Kharal, Renewable Energy Resources Penetration
within Gridâ, First International Conference on High Performance Energy Efficient
Buildings and Homes (HPEEBH 2018), UET Lahore.