interactions between dynamic line rating and …. mohamed emad farrag glasgow caledonian university...
TRANSCRIPT
Introduction: Dynamic line rating enhances
efficiency of transmission lines among many other benefits
such as:
Reducing power transmission overall losses and costs
Increases control of system’s stability and inertia
However….
There are some protection co-ordination challenges to
overcome ;
Mismatch between increased temperature allowance of
overhead lines and those of current transformers.
Impact of this mismatch on protection zone reach,
potentially leading to under reach during a fault which
may lead to cascading a fault upstream heathy section.
Abdallah Abdaelbaset
Scottish & Southern Electricity Networks
Interactions between Dynamic Line Rating and Protection Coordination in Transmission System of Northern Scotland
[1] A.Abdaelbaset, M.Farrag, D.Hepburn, S.Farokhi, “Overview of On-line and Off-line Ampacity
Identification Techniques of Bare Overhead Transmission Line”, 45th University Power Engineering
Conference, Coimbra, Portugal, September 2016.
[2] DA Tziouvaras, “Protecting Mutually Coupled Transmission Lines: Challenges and Solutions”, 67th
Annual Conference for Protective Relay Engineers” , TX, USA, March 2014
[3] BS 7626 – Clause 9 “Specification for Current transformers — (Implementation of CENELEC HD 553
S2)”, BS Std. 1993
[4] ABB -Instrument Transformers Technical Information and Application Guide- Accessed online
07DEC16, https://library.e.abb.com/public/e2462bd7f816437ac1256f9a007629cf/ITTechInfoAppGuide.pdf
[5] BS IEC 60076-7- “Loading guide for oil-immersed power transformers”, BS IEC Std 2005
Ahmed Mohamed
Scottish & Southern Electricity Networks
Mahmoud AbouElkasem
Scottish & Southern Electricity Networks
Dr. Mohamed Emad Farrag
Glasgow Caledonian University
Frequency response: Time required by power generation depends requires careful
consideration, DLR technology facilitates better economical generation despatch.
Generation Technology Response Time
Pumped Storage ~ Seconds
Gas Turbines ~ Minutes
CCGT ~ 6 Hours
Coal Fired Plants ~12 – 24 Hours
Nuclear Power station ~ 48 HoursConclusions : To maintain high degree
of accuracy of DLR systems it is essential to
undertake the following steps.
o Measuring the bare overhead line conductor
impedances using an LCR meter at high
temperatures 90 ◦C. This should give
utilities accurate impendence values
reflecting real life applications and help them
calculate protection zone more accurately.
o Consider employing remote protection
adjustment technologies, beside reduced
need of operational personnel travel to sites
and increased flexibility of control. This will
enable safe deployment of DLR systems and
reduce risks associated with protection over
/under reach.
o Consideration should be made for using
current transformers with thermally upgraded
paper insulation that meets criteria defined in
ANSI/IEEE C57.100. This technology will
support increasing ampacity of the line under
consideration node to node.
o Most modern digital relays are equipped with
thermal transducers and are capable of
initiating a trip signal when pre-set criteria is
met.
o Installing a weather station coupled with
conductor thermocouple in part of line under
investigation will prove thermal calculations
in real time.
o Installation of partial discharge monitoring
system can greatly reduce reliability through
establishing a detection system to capture
any degradation in performance of
insulation.
Discussion:Overhead line conductor
High Voltage circuit breaker
The mismatch in temperature allowance between overhead line conductor and current
transformer can contribute towards reducing value utilities can obtain from adopting
similar technology.
Relay
Thermal Conductor allowance = Ambient temperature -
cooling effect of wind & rain + Joule heating (average
allowance for a typical 132kV newly installed line is 90◦C )
Thermal current transformer allowed
thermal rise = Ambient temperature
– cooling effect of oil + Joule heating
(BS7626 recommends to limits this
value to no more than 60◦C )
Protection zone reach is pre-set
based on 20 ◦C measured
impedance
Protection Zone Reach: Protection
zones of power systems are sensitive to changes in
resistance which are caused by change of conductor
temperature, hence the more accurate the thermal
ratings of the conductor are calculated the greater the
accuracy and fault discrimination capability the relays
will offer when DLR system is employed. It is also
important to underline that backup over current
protection will also be effected because choice of
protection setting may not reflect ground real time
conditions.
Example of power generation response and
synchronizing lead times
Temperature & Resistance:
R = Rref [ 1+ α (T – Tref ) ]Where;
R Conductor resistance at temperature “T”
Rref Conductor resistance at reference
temperature.
α Temperature coefficient of resistance.
T Conductor temperature
Tref Reference temperature at which α is
specified at.