Power Systems

More information about this series at http://www.springer.com/series/4622

Tharangika BambaravanageAsanka Rodrigo • Sisil Kumarawadu

Modeling, Simulation,and Controlof a Medium-ScalePower System

123

Tharangika BambaravanageDepartment of Electrical EngineeringUniversity of MoratuwaMoratuwaSri Lanka

Asanka RodrigoDepartment of Electrical EngineeringUniversity of MoratuwaMoratuwaSri Lanka

Sisil KumarawaduDepartment of Electrical EngineeringUniversity of MoratuwaMoratuwaSri Lanka

ISSN 1612-1287 ISSN 1860-4676 (electronic)Power SystemsISBN 978-981-10-4909-5 ISBN 978-981-10-4910-1 (eBook)https://doi.org/10.1007/978-981-10-4910-1

Library of Congress Control Number: 2017952534

© Springer Nature Singapore Pte Ltd. 2018This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or partof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmissionor information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilarmethodology now known or hereafter developed.The use of general descriptive names, registered names, trademarks, service marks, etc. in thispublication does not imply, even in the absence of a specific statement, that such names are exempt fromthe relevant protective laws and regulations and therefore free for general use.The publisher, the authors and the editors are safe to assume that the advice and information in thisbook are believed to be true and accurate at the date of publication. Neither the publisher nor theauthors or the editors give a warranty, express or implied, with respect to the material contained herein orfor any errors or omissions that may have been made. The publisher remains neutral with regard tojurisdictional claims in published maps and institutional affiliations.

Printed on acid-free paper

This Springer imprint is published by Springer NatureThe registered company is Springer Nature Singapore Pte Ltd.The registered company address is: 152BeachRoad, #21-01/04GatewayEast, Singapore 189721, Singapore

ToMr. D.S.C. Wijesekara&Mrs. D.W. Jayasinghe

Acknowledgements

We are very thankful to the Institute of Technology, University of Moratuwa, forthe financial support provided for this research study.

Heartfelt sincere thanks are due to Dr. (Miss) Lidula Vidanagamage for helpwith PSCAD simulations during the course of this work.

We would also like to extend our sincere thanks to the faculty and the staff of theDepartment of Electrical Engineering, University of Moratuwa, for providingresources and facilitating the research study.

We are very much thankful to the System Control Centre of the CeylonElectricity Board (CEB), for the invaluable discussions and help with data duringthis research study.

Last but not least, a precious thank-you goes to our family members for theirlove, encouragement, and constant support all throughout.

vii

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Literature Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1 Structure of an Electrical Power System. . . . . . . . . . . . . . . . . . . . 52.2 Power System Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 Why Power System Instability Situations Occur? . . . . . . . . . . . . . 62.4 Disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.4.1 Effects of the Disturbances on the Power System . . . . . . . 82.5 Reliability of a Power System . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.6 Quality of a Power System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.6.1 Addressing Instability Situations Due to Perturbationsin the Power System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.6.2 Classification of Power System Dynamics . . . . . . . . . . . . . 112.7 Process for Generation-Load Balance . . . . . . . . . . . . . . . . . . . . . . 14

2.7.1 Primary Control (Is by Governors) . . . . . . . . . . . . . . . . . . 152.7.2 Secondary Control (Is by Automatic

Generation Controls) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.7.3 Tertiary Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.7.4 Time Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.8 Under-Frequency Load Shedding . . . . . . . . . . . . . . . . . . . . . . . . . 25

3 Modelling the Power System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.1 Power System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.2 Configuring Power System Components/Mathematical

Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.2.1 Transmission Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343.2.2 Under-Ground Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2.3 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423.2.4 Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.2.5 Exciters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

ix

3.2.6 Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.2.7 Governors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

3.3 Control System of the Overall Power System . . . . . . . . . . . . . . . . 783.3.1 LS Logic1 Control System Module . . . . . . . . . . . . . . . . . . 783.3.2 U_Frequency Control System Module . . . . . . . . . . . . . . . . 863.3.3 Add_Ld Control System Module . . . . . . . . . . . . . . . . . . . 86

3.4 Verifying the Simulation Model Performance . . . . . . . . . . . . . . . . 873.4.1 Steady State Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 873.4.2 Generator Tripping/Sudden Generation

Deficit Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

4 Designing the Load Shedding Scheme . . . . . . . . . . . . . . . . . . . . . . . . 974.1 Overview of the Power System of Sri Lanka . . . . . . . . . . . . . . . . 974.2 Identification of Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

4.2.1 Power System Regulations and Practice of Sri Lanka . . . . 984.2.2 Identifying Settling Frequency . . . . . . . . . . . . . . . . . . . . . 994.2.3 Deciding the Number of Steps in the Load Shedding

Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994.2.4 First Step of Load Shedding Scheme . . . . . . . . . . . . . . . . 1004.2.5 Identifying When to Implement Load Shedding Based

on Rate of Change of Frequency (ROCOF) . . . . . . . . . . . . 1004.2.6 Delay Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

4.3 Ahsans’ Scheme as a Pilot Model [56] . . . . . . . . . . . . . . . . . . . . 1044.4 Proposed Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

4.4.1 Load Shedding Scheme-I (Based on Prevailing FacilitiesAvailable with the CEB) . . . . . . . . . . . . . . . . . . . . . . . . . 107

4.4.2 Load Shedding Scheme-II (Based on Disintegrationof the Power System) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215.1 Discussion: Load Shedding Scheme-I with Generation Deficit

of 829.6 MW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215.2 Discussion: Load Shedding Scheme-II with Generation Deficit

of 495.14 MW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235.2.1 Performance of the National Grid . . . . . . . . . . . . . . . . . . . 1245.2.2 Performance of Island Rantembe . . . . . . . . . . . . . . . . . . . 1265.2.3 Performance of Island Matugama . . . . . . . . . . . . . . . . . . . 1305.2.4 Performance of Island Embilipitiya . . . . . . . . . . . . . . . . . . 1355.2.5 Performance of Island Kiribathkumbura . . . . . . . . . . . . . . 139

5.3 Performance Comparison on Selected Load SheddingSchemes (LSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

x Contents

Appendix A: Transmission Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Appendix B: Composite Loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Appendix C: Generation Characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Appendix D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Contents xi

About the Authors

Tharangika Bambaravanage obtained her B.Sc.(Engineering), M.Eng. inElectrical Engineering, and M. Phil. in Power System Stability and Control from theUniversity of Moratuwa, respectively, in 1998, 2005, and 2017. She has been aSenior Lecturer in Electrical Engineering at the Institute of Technology, Universityof Moratuwa, since 2017.

Asanka Rodrigo obtained his B.Sc.(Hons) and M.Sc. in Electrical Engineering,respectively, in 2002 and 2004, from the University of Moratuwa, and Ph.D. inIndustrial Engineering from Hong Kong University of Science and Technology in2010. He has been a Senior Lecturer in Electrical Engineering at the Faculty ofEngineering of University of Moratuwa since 2010.

Sisil Kumarawadu obtained his B.Sc.(Hons) in Electrical Engineering from theUniversity of Moratuwa in 1996. He obtained his M.Eng. in advanced SystemsControl Engineering and Ph.D. in Robotics and Intelligent Systems in 2000 and2003, respectively, from Saga National University, Japan. From April 2003 to July2005, he was with Intelligent Transportation Systems Research Center, NCTU,Taiwan, as a postdoctoral research fellow. Currently, he is a Professor in ElectricalEngineering at the University of Moratuwa.

xiii

List of Figures

Fig. 2.1 Structure of an electrical power system . . . . . . . . . . . . . . . . . . . 6Fig. 2.2 p-model of a transmission-line. . . . . . . . . . . . . . . . . . . . . . . . . . 9Fig. 2.3 A generic model of a generator system . . . . . . . . . . . . . . . . . . . 12Fig. 2.4 Typical time intervals for analysis and control of the most

important power system dynamic phenomena . . . . . . . . . . . . . . 13Fig. 2.5 Generation load balance in different time horizons . . . . . . . . . . 14Fig. 2.6 Power system automatic generation control . . . . . . . . . . . . . . . . 15Fig. 2.7 Equilibrium points for an increase in the power demand . . . . . . 17Fig. 2.8 A typical speed power characteristic of a governor system . . . . 19Fig. 2.9 Turbine speed–droop characteristics for various settings

of Pref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Fig. 2.10 Power balance of a control area. . . . . . . . . . . . . . . . . . . . . . . . . 22Fig. 2.11 Frequency and interchange flow deviations for one area . . . . . . 24Fig. 2.12 Power system responses due to a load-generation

imbalance situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Fig. 2.13 Fink and Carlsen diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Fig. 3.1 Issues of mathematical modelling of a power system/power

system components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Fig. 3.2 PSCAD windows corresponding to transmission line from

Randenigala to Rantembe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Fig. 3.3 A part of the power system comprising the ‘Rand-Rant’

transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Fig. 3.4 Different layers of insulation and protective materials of an

underground cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Fig. 3.5 The cable that links Colombo Fort substation

and Kelanitissa power station bus-bars, as appearin the simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Fig. 3.6 PSCAD windows corresponding to power transmission cablefrom Kelanitissa to Colombo Fort substation. . . . . . . . . . . . . . . 41

xv

Fig. 3.7 132 kV under-ground cable lay-out corresponding to‘Keltissa-Col_F’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Fig. 3.8 Generator transformers located at the Kotmale power station,as appear in the PSCAD simulation model . . . . . . . . . . . . . . . . 46

Fig. 3.9 PSCAD generator transformer windows corresponding to theKotmale power station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Fig. 3.10 Classification of synchronous generators referringto their speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Fig. 3.11 Configuration of a generating unit . . . . . . . . . . . . . . . . . . . . . . . 48Fig. 3.12 Relationship between mechanical and electrical power

and speed change. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Fig. 3.13 Block-diagrams demonstrating the effect of change in

frequency sensitive and non-frequency sensitive load . . . . . . . . 52Fig. 3.14 A generator unit at Kotmale power station with its hydro

turbine, governor and exciter . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Fig. 3.15 Values used with PSCAD window corresponding

to Kotmale generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Fig. 3.16 Basic types of exciters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Fig. 3.17 Block diagram of the excitation and AVR system . . . . . . . . . . . 58Fig. 3.18 Cascaded DC generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Fig. 3.19 Exciter model ‘AC1A’ used for the simulation . . . . . . . . . . . . . 60Fig. 3.20 IEEE Alternator Supplied Rectifier Excitation System

#1 (AC1A) as in PSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Fig. 3.21 The excitation system with AC alternator and the uncontrolled

rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Fig. 3.22 Values used with PSCAD windows in configuring

Ac1A exciters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Fig. 3.23 Configuration of a tandem compound single-reheat

steam turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Fig. 3.24 Control system of a single reheat tandem compound steam

turbine as per [11] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Fig. 3.25 Generic turbine model including intercept valve effect as

given in PSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Fig. 3.26 Generic model for steam turbines as per [11] . . . . . . . . . . . . . . 68Fig. 3.27 Values used with PSCAD windows in configuring

Steam_Tur_2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Fig. 3.28 ‘Steam_Tur_2’ Generic turbine model including intercept

valve effect (TUR2) used for the power system simulation . . . . 70Fig. 3.29 Hydro turbine model used in power system

simulation—‘Non-elastic water column without surgetank (TUR1)’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Fig. 3.30 Block diagram of control system of ‘Non-elastic watercolumn without surge tank’, TUR1, PSCAD simulationmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

xvi List of Figures

Fig. 3.31 Values used with PSCAD windows in configuringHydro_Tur_1 (Non-elastic water column without surgetank (TUR1)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Fig. 3.32 Governor models used in PSCAD . . . . . . . . . . . . . . . . . . . . . . . 73Fig. 3.33 Block diagram of control system of Steam_Gov_2

(Mechanical-hydraulic controls), PSCAD simulation model. . . . 74Fig. 3.34 Block diagram of ‘Mechanical-hydraulic controls governing

system’ as per [11] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Fig. 3.35 Block diagram of control system of governor

Electro-Hydraulic Controls (GOV3), as per PSCADsimulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Fig. 3.36 Block diagram of ‘Electro-hydraulic controls governingsystem’ as per [11] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Fig. 3.37 Governor models used in PSCAD . . . . . . . . . . . . . . . . . . . . . . . 76Fig. 3.38 Block diagram of the control system of hydro governor

‘Hydro_Gov_1 (Mechanical-hydraulic controls (GOV1)as per PSCAD simulation model) . . . . . . . . . . . . . . . . . . . . . . . 77

Fig. 3.39 Block diagram of governing system for hydraulic turbineas per [3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Fig. 3.40 Hydro_Gov_3 (Enhanced controls for load rejection studies(GOV3) of PSCAD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Fig. 3.41 Steam_Governor_2 and Steam_Governor_3. . . . . . . . . . . . . . . . 81Fig. 3.42 Parameter values for hydro turbine governor types used

in the simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Fig. 3.43 PSCAD windows corresponding to the Chebyshev filter

configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Fig. 3.44 PSCAD windows corresponding to Butterworth filter

configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Fig. 3.45 The Chebyshev and Butterworth filters used . . . . . . . . . . . . . . . 85Fig. 3.46 Derivative function in PSCAD . . . . . . . . . . . . . . . . . . . . . . . . . 85Fig. 3.47 PSCAD model used to calculate the df/dt

of the power system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Fig. 3.48 Control circuit which senses the system frequency and

to operate circuit breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86Fig. 3.49 System responses to a sudden generation deficit

of 23.18 MW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Fig. 3.50 Implementing a sudden load addition

with the simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Fig. 3.51 Power system performance during steady state . . . . . . . . . . . . . 91Fig. 3.52 System frequency, system voltage and generator power

output, after tripping off some selected generator setsand loads from the simulation model. . . . . . . . . . . . . . . . . . . . . 93

Fig. 3.53 Frequency profiles during a tripping offof a coal power plant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

List of Figures xvii

Fig. 4.1 Time taken to reach the minimum df/dt due to a coal powerplant tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Fig. 4.2 Flow chart of the CEB load shedding scheme consideringtime delays for relay and circuit breaker operation . . . . . . . . . . 103

Fig. 4.3 Flow chart illustrating different steps of the techniqueintroduced by Ahsan et al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Fig. 4.4 Power system of Sri Lanka considering as a groupof small islands and the national grid . . . . . . . . . . . . . . . . . . . . 106

Fig. 4.5 Time line diagram that demonstrates the relayand circuit breaker operating times . . . . . . . . . . . . . . . . . . . . . . 107

Fig. 4.6 System frequency variation against Time, duringa forced generation tripping of 243.08 MW. . . . . . . . . . . . . . . . 108

Fig. 4.7 Flow chart demonstrating the load shedding scheme-I. . . . . . . . 109Fig. 4.8 Flow chart of the Phase-I of load shedding scheme-II . . . . . . . . 112Fig. 4.9 Flow chart of the Phase-II of load shedding scheme-II that

corresponds to Island-Rantembe . . . . . . . . . . . . . . . . . . . . . . . . 120Fig. 5.1 Frequency profile with the implementation of the LSS-I in

response to a generation deficit of 829.6 MW . . . . . . . . . . . . . . 122Fig. 5.2 Voltage profile of the national grid . . . . . . . . . . . . . . . . . . . . . . 122Fig. 5.3 Rate of change of frequency after the disturbance . . . . . . . . . . . 123Fig. 5.4 Stages involved in the load shedding scheme . . . . . . . . . . . . . . 123Fig. 5.5 Power outputs of some selected generators . . . . . . . . . . . . . . . . 124Fig. 5.6 Frequency profile of the national grid with the disturbance . . . . 125Fig. 5.7 Voltage profile of the national grid during and after the

disturbance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Fig. 5.8 Rate of change of frequency after the disturbance . . . . . . . . . . . 126Fig. 5.9 Stages got implemented in the load shedding scheme-II.

4 nos. of stages of the phase-I and the disintegration of thepower system. The stage 7 corresponds to the 5th stage whichleads for disintegration of the power system . . . . . . . . . . . . . . . 126

Fig. 5.10 Some of the power plants that got tripped-off and generationoutput of some selected generators . . . . . . . . . . . . . . . . . . . . . . 127

Fig. 5.11 Island Rantembe control station. . . . . . . . . . . . . . . . . . . . . . . . . 127Fig. 5.12 Control logic used to perform ‘Generator Rantembe’

as a swing generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128Fig. 5.13 Frequency profile of Island Rantembe . . . . . . . . . . . . . . . . . . . . 129Fig. 5.14 Voltage profile of Island Rantembe . . . . . . . . . . . . . . . . . . . . . . 129Fig. 5.15 Rate of change of frequency of Island Rantembe during

disintegration of the power system . . . . . . . . . . . . . . . . . . . . . . 130Fig. 5.16 Implementation of the load shedding scheme

of Island Rantembe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Fig. 5.17 Instant the reactance got connected to the

‘Island Rantembe—power system’. . . . . . . . . . . . . . . . . . . . . . . 131

xviii List of Figures

Fig. 5.18 Implementation of reactive power compensation of ‘IslandRantembe-Power System’ with the simulation model . . . . . . . . 131

Fig. 5.19 Inductor used for reactive power compensation of ‘IslandRantembe-Power System’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Fig. 5.20 Power generation of generator Rantembe against Time, afterislanding operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Fig. 5.21 Reactive power generation of the generator Rantembe withthe isochronous governor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Fig. 5.22 Island Matugama control station . . . . . . . . . . . . . . . . . . . . . . . . 133Fig. 5.23 Control logic used to perform ‘Generator Kukule-1’ as a

swing generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Fig. 5.24 Frequency profile of Island Matugama . . . . . . . . . . . . . . . . . . . 135Fig. 5.25 Voltage profile of the Island Matugama. . . . . . . . . . . . . . . . . . . 135Fig. 5.26 Rate of change of frequency of ‘Island Matugama’ during

disintegration of the power system . . . . . . . . . . . . . . . . . . . . . . 136Fig. 5.27 Implementation of the load shedding scheme

of Island Matugama. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Fig. 5.28 Instance the reactance got connected to the

‘Island Matugama—power system’ . . . . . . . . . . . . . . . . . . . . . . 137Fig. 5.29 Implementation of reactive power compensation

of ‘Island Matugama—power system’with the simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Fig. 5.30 Inductor used for reactive power compensation of ‘IslandMatugama - Power System’. . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Fig. 5.31 Power generation of generator Kukule-1 against Time, afterislanding operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Fig. 5.32 Reactive power generation of the generator Kukule-1with the isochronous governor. . . . . . . . . . . . . . . . . . . . . . . . . . 138

Fig. 5.33 Island Embilipitiya control station . . . . . . . . . . . . . . . . . . . . . . . 139Fig. 5.34 Control logic used to perform ‘Generator Samanalawewa-1’

as a swing generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140Fig. 5.35 Frequency profile of Island Embilipitiya . . . . . . . . . . . . . . . . . . 141Fig. 5.36 Voltage profile of Island Embilipitiya . . . . . . . . . . . . . . . . . . . . 141Fig. 5.37 Rate of change of frequency of ‘Island Embilipitiya’

during disintegration of the power system . . . . . . . . . . . . . . . . . 142Fig. 5.38 Implementation of the load shedding scheme of Island

Embilipitiya . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142Fig. 5.39 Instance the reactance got connected to the ‘Island

Embilipitiya—power system’ . . . . . . . . . . . . . . . . . . . . . . . . . . . 143Fig. 5.40 Implementation of reactive power compensation of ‘Island

Embilipitiya—power system’ with the simulation model . . . . . . 143Fig. 5.41 Inductor used for reactive power compensation of ‘Island

Embilipitiya - Power System’ . . . . . . . . . . . . . . . . . . . . . . . . . . 143

List of Figures xix

Fig. 5.42 Power generation of generator Samanalawewa-1 againstTime, after islanding operation . . . . . . . . . . . . . . . . . . . . . . . . . 144

Fig. 5.43 Reactive power generation of the generator Samanalawewa-1with the isochronous governor. . . . . . . . . . . . . . . . . . . . . . . . . . 144

Fig. 5.44 Island Kiribathkumbura control station . . . . . . . . . . . . . . . . . . . 145Fig. 5.45 Control logic used to perform ‘Generator Ukuwela’

as a swing generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146Fig. 5.46 Frequency profile of Island Kiribathkumbura. . . . . . . . . . . . . . . 147Fig. 5.47 Voltage profile of Island Kiribathkumbura. . . . . . . . . . . . . . . . . 147Fig. 5.48 Rate of change of frequency of ‘Island Kiribathkumbura’

during disintegration of the power system . . . . . . . . . . . . . . . . . 148Fig. 5.49 Implementation of the load shedding scheme of Island

Kiribathkumbura . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148Fig. 5.50 Instance the reactance got connected to the ‘Island

Kiribathkumbura-Power System’ . . . . . . . . . . . . . . . . . . . . . . . . 149Fig. 5.51 Implementation of reactive power compensation

of ‘Island Kiribathkumbura—power system’with the simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Fig. 5.52 Inductor used for reactive power compensationof ‘Island Kiribathkumbura - Power System’. . . . . . . . . . . . . . . 149

Fig. 5.53 Power generation of generator Ukuwela against Time,after islanding operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Fig. 5.54 Reactive power generation of the generator Ukuwelawith the isochronous governor. . . . . . . . . . . . . . . . . . . . . . . . . . 150

Fig. A.1 a Two-port p equivalent circuit of an approximatedtransmission line. b Corresponding phasor diagram.c Real power and reactive power characteristics . . . . . . . . . . . . 160

Fig. B.1 Illustration of the definition of voltage sensitivity . . . . . . . . . . . 164Fig. C.1 Generation characteristic as the sum of speed–droop

characteristics of all the generation units . . . . . . . . . . . . . . . . . . 166Fig. C.2 Speed–droop characteristic of a turbine

with an upper limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167Fig. C.3 Influence of the turbine upper power limit and the spinning

reserve allocation on the generation characteristic . . . . . . . . . . . 168Fig. C.4 Static system generation characteristic . . . . . . . . . . . . . . . . . . . . 168

xx List of Figures

List of Tables

Table 3.1 Conductor types used in the transmission networkof Sri Lanka . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Table 3.2 RXY values as given in [41], for the transmission line‘Rand-Rant’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Table 3.3 Physical parameter data used for configuring the cablesin the simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Table 3.4 Resistivity of metals used in the cables . . . . . . . . . . . . . . . . . . . 39Table 3.5 Permittivity of insulation materials used in the cables . . . . . . . . 40Table 3.6 Data used for configuring under-ground/submarine cables. . . . . 42Table 3.7 Typical per-unit values of transformers . . . . . . . . . . . . . . . . . . . 43Table 3.8 Per-unit values of transformer parameters . . . . . . . . . . . . . . . . . 44Table 3.9 Inertia constants of different types of generators . . . . . . . . . . . . 55Table 3.10 Inertia constants of generators obtained from the CEB . . . . . . . 56Table 3.11 Inertia constants used for the units considered

in the simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Table 3.12 Typical values in Fig. 3.26 corresponding to Fig. 3.25 . . . . . . . 69Table 3.13 Comparison of time constants and gains in Fig. 3.24

(as per [11]-Kundur’s) and Fig. 3.25 (PSCAD) . . . . . . . . . . . . . 69Table 3.14 Values used for the parameters in the control system

of ‘Generic turbine Model including intercept valveeffect as given in PSCAD’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Table 3.15 Governor Models of PSCAD used in controlling steamand hydro turbines of the simulation of the Power systemof Sri Lanka . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Table 3.16 Typical values for the parameters in Mechanical-HydraulicControls (GE) (GOV2) model in PSCAD . . . . . . . . . . . . . . . . . 75

Table 3.17 Typical values for the parameters in Electro-HydraulicControls (GE) (GOV2) model of a steam turbinein PSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

xxi

Table 3.18 Typical values for the parameters in Mechanical-HydraulicControls (GE) (GOV1) model of a hydro turbinein PSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Table 3.19 Values used to configure the governor model ‘Hydro_Gov_3(enhanced controls for load rejection studies (GOV3))’ . . . . . . . 80

Table 3.20 Maximum overshoot during start of source and steady statefrequency obtained with different Chebyshev filter settings . . . . 82

Table 3.21 Actual generator outputs and simulation model’s generatoroutputs corresponding to the load flow on the 13th March,2013 during day time peak demand. . . . . . . . . . . . . . . . . . . . . . 89

Table 3.22 Removed generator outputs and loads from the PSCADsimulation model designed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Table 4.1 Present Ceylon Electricity Board (CEB) loadshedding scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Table 4.2 Time delays corresponding to each load shedding actionin the simulated present CEB load shedding scheme . . . . . . . . . 104

Table 4.3 Ahsans’ LS Scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106Table 4.4 Proposed load shedding scheme-I with time delays

corresponding to each load shedding action. . . . . . . . . . . . . . . . 110Table 4.5 Generators took part in the forced outage with their

corresponding generation capacities . . . . . . . . . . . . . . . . . . . . . . 110Table 4.6 Phase-I of proposed LSS-II with time delays corresponding

to each LS action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111Table 4.7 Generators took part in the forced outage with their

corresponding generation capacities . . . . . . . . . . . . . . . . . . . . . . 113Table 4.8 Generators which were tripped off to balance the power

generation and demand of the National Grid . . . . . . . . . . . . . . . 114Table 4.9 Generators in continuous operation in the National Grid

immediately before and after the disintegrationof the power system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Table 4.10 Loads connected to each grid substation, whichwere involved in the Phase-I of the load shedding scheme . . . . 116

Table 4.11 Loads connected to each substation in the National Grid,with a 40% of the total demand. . . . . . . . . . . . . . . . . . . . . . . . . 117

Table 4.12 Inductive reactance required to be connected for reactivepower compensation in Island Matugama . . . . . . . . . . . . . . . . . 117

Table 4.13 Inductive reactance required to be connected for reactivepower compensation in Island Rantembe. . . . . . . . . . . . . . . . . . 118

Table 4.14 Inductive reactance required to be connected for reactivepower compensation in Island Embilipitiya . . . . . . . . . . . . . . . . 118

Table 4.15 Inductive reactance required to be connected for reactivepower compensation in Island Kiribathkumbura . . . . . . . . . . . . 119

Table 4.16 Phase-II of proposed load shedding scheme-II with timedelays corresponding to Island Rantembe . . . . . . . . . . . . . . . . . 119

xxii List of Tables

Table 4.17 The excess demand and amounts of loads to be shedin shedding stages in each island during disintegrationof the power system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Table 5.1 Simulation results of present CEB LSS, Proposed LSS-I andProposed LSS-II when applied for the Power System ofSri Lanka, under different forced power generation outages . . . 151

List of Tables xxiii

Abstract

Emergency load shedding for preventing frequency degradation is an establishedpractice all over the world. The objective of load shedding is to balance load andgeneration of a particular Power System (PS). In addition to the hydro and thermalgenerators each with less than 100 MW, today, the PS of Sri Lanka is comprised ofthree coal power plants: Each has a generation capacity of 300 MW; Yugadanavicombined cycle power plant (300 MW generation capacity) and a considerablyextended transmission network. To cater consumers with high-quality electricity, areliable PS is a must. Therefore, it has become timely necessity to review theperformance of the present Ceylon Electricity Board (CEB) Under Frequency LoadShedding Scheme (UFLSS) and suggest amendments where necessary.

The objective of this research is to explore a better UFLSS which can faceprobable contingencies and maintain stability of the system while catering moreconsumers. The suggested UFLSSs can address the recent changes taken place inthe Sri Lanka PS too.

A simulation of the PS of Sri Lanka was designed with software PSCAD. Itsvalidity was checked through implementing actual scenarios which took place inthe PS under approximately equal loaded conditions and by comparing the simu-lated results and actual results. Then, a performance analysis was done for theCEB UFLSS which is being implemented in Sri Lanka. Having identified itsdrawbacks, the new UFLSSs (LSS-I and LSS-II) were suggested.

The Load Shedding Scheme-I (LSS-I) is designed based on PS frequency and itsderivative under abnormal conditions. Without doing much modification to theprevailing UFLSS, and utilizing the available resources, the suggested LSS-I can beimplemented.

The LSS-II gives priority for 40% of the system load for continuous powersupply, and it is comprised of two stages. During the stage-I, approximately 30%of the load is involved with the Load Shedding action. During the stage-II, thedisintegration of the PS is done. This involves the balance 30% of the load. At 48.6Hz, the disintegration of the PS takes place. By disintegrating the PS at theabove-mentioned frequency, all islands as well as the national grid can be brought

xxv

to steady-state condition without violating the stability constraints of the SriLanka PS. During disintegration of the PS, special attention must be paid for:

• Generation and load balance in each island and in the national grid.• Reactive power compensation in islands and in the national grid.• Tripping off of all isolated transmission lines (which are not connected to

effective loads).

Through simulations, the effectiveness of the UFLSSs was evaluated. Theydemonstrate better performance compared to that of the currently implementingCEB scheme. Results highlight that the UFLSS should exclusively be specific for aparticular PS. It depends on factors such as PS practice, PS regulations, largestgenerator capacity, electricity consumption pattern etc.

xxvi Abstract