Preferential Subject #3 Protection and Control of Series Compensated Networks S U M M A R Y Special Reporter: Graeme Topham South Africa Study Committee B5 Colloquium 2005 September 14 – 16 Calgary, CANADA

SUMMARY STUDIES SIMULATION DATA

Q1: Main utility considerations when deciding to series compensate a transmission line and/or what are the challenges faced? JP: Design considerations 275 kV double circuit SC line:  Simulation study: Degree of compensation vs. Stable transmission capacity  Special directional scheme for backup  Large scale field tests GS: Introducing SC more economical than additional line CA: Must be careful in choice of relays. Tests important CA: SC reduces influence of Geo-magnetic induced currents

Q2: What economic and/or environmental issues deter the implementation of series compensation? SE: Environmental issues can influence preferred location of SC

Q3: Experiences of other unique SC distance relay applications where special adjustments to settings and/or logic are required? BR: Extensive simulation tests -> necessity to refine logic and/or settings At lower voltages tests expensive -> tools needed CN: Deviation of power frequency component relay. Zero sequence source impedance artificially decreased. Adaptive functionality. JP: Special directional scheme. Based on memory function -> operating time delay for V inversion. Three directional distance elements required for SC double-circuit lines. Numerical technology allowed simplification.

Q3: Experiences of other unique SC distance relay applications where special adjustments to settings and/or logic are required? SE: Distance relay model – basis for problems for dealing with SC UK:  Special setting when accurate V measurement unavailable  Special polarizing V for direction decision  Cross differential relay proposed as better solution for double circuit lines  Weak infeed not a problem  New capacitor voltage calculation technique

Q3: Experiences of other unique SC distance relay applications where special adjustments to settings and/or logic are required? US: Formula based on gap voltage to come to a security factor for setting Z1 CA: Current diff relay better than distance relay SE: Margin for Z1 dependent on compensation degree

Q4: What analysis tools are available to utilities to assist in evaluating distance relay performance on SC applications prior to the purchase or choice of a particular relay type? BR: Use of RSim tool to ‘assemble’ a virtual relay. Good results for relays where enough info available. Cooperation between manufacturers and users SE: SS simulations (PSSE / CAPE) not suitable EMTP - insufficient relay details Only viable option is simulator tests US: Tools – relay manual; test report; test data base (COMTRADE files); simulation US: Real-time simulation - system specific and must be accurately CA: HyperSim

Q4: What analysis tools are available to utilities to assist in evaluating distance relay performance on SC applications prior to the purchase or choice of a particular relay type? CN: Digital model for development. Physical models for testing CA: Relay model info will allow users to see margin -> added security US: DLL file for EMPT testing

Q5: Besides zero sequence current compensation, what other techniques have been successfully applied to distance relays to resolve the impedance measurement inaccuracy on SC parallel lines? US: Supervise impedance measurement with superimposed direction function SE: China – 4 x 500 kV systems on same tower. Grounding switches?

Q6: What are the current experiences with using the weak infeed protection function, particularly in SC line protection applications? BR: Many problems with weak infeed function. How to determine temporary weak infeed terminals during long duration major disturbance and restoration? 2006 Session? CA: Agree weak infeed trip insecure Recommendation to separate WI from permissive trip Echo function in POTT schemes

Q6: What are the current experiences with using the weak infeed protection function, particularly in SC line protection applications? SE: WI important feature. Must consider all necessary precautions to prevent unwanted operations

Q7: What are the main technical difficulties with accurate fault location on SC lines and what fault location techniques are currently being successfully employed? JP: Experience with one- and two-terminal methods. Latter better than differential equation based algorithm. SE: Impedance method inaccurate especially when compensation degree switched. Travelling wave method found to be most accurate

Q8 a): What methodologies are used to optimize settings for series compensated line applications? SE: Real-time simulations to verify total protection scheme SE: Thyristor controlled capacitor needs to be correctly simulated when testing line protection

Q8 b): What are the requirements of utilities in terms of certification tests for relays and/or protection systems before applying these to SC lines? AU: Distance relay problems Transient fault studies essential Automatic test tool very useful BR: Real-time digital simulation to verify behavior and performance of relays. Also used to optimize settings. US: High quality records to verify models

Q9: What are utility experiences with non- distance protection applications on series compensated transmission lines? JP: FM current differential as main protection with directional distance as back-up

Q10: What are the advantages, disadvantages, technical challenges and cost implications of using non-distance protection when compared to using distance protection on SC applications? JP: Advantages of using current-based relay as main protection Operating time of back-up distance well co- ordinated 270 line faults cleared by Main. Backup not involved and no misoperations

Q10: What are the advantages, disadvantages, technical challenges and cost implications of using non-distance protection when compared to using distance protection on SC applications? UK: High charging current possible problem for current diff. Cross differential relay proposed option for double circuit lines. Examples of new relay principles being researched – surge impedance, noise generated protection and boundary protection techniques Importance of dynamic tests and international research and development collaboration

Q10: What are the advantages, disadvantages, technical challenges and cost implications of using non-distance protection when compared to using distance protection on SC applications? US: Comparison of distance protection (with and without comms) and directional comparison and importance of performance and cost assessment SE: Charging current compensation no longer a problem. Trend towards current differential.

Q11 a): What are the current experiences with auto- reclosing on series compensated transmission lines? Q11 b): What are the technical challenges and proposed solutions? SE: Duty cycles for thyristor controlled capacitor bank elements outlined. Challenge relating to multi-pole tripping and sequential reclosing. SE: Good experience with ARC (3-pole tripping) even on TCSC

BR: No UPFCs, but TCSCs successfully applied – No particular problems. Line protection set according to worst conditions Q12: Have there been any problematic protection issues relating to the use of UPFCs experienced by other utilities and what solutions are available?

Q13: What other novel theoretical tools are available to assist in the analysis and understanding of SC networks? SE: Practical results of complex subject of informational analysis in Russia

Q14: What influences of shunt capacitor banks on protection measurement are reported and how are the effects mitigated? CH: Large impact on the circulating currents and transient behaviour during line faults under weak infeed conditions. Close-to-zero V faults make direction determination difficult More than 1 polarization signal for direction decision recommended

PS-3 Concluding Comments Evidence of continued valuable work being done to improve the performance of the protection, control and monitoring of series compensated networks New challenges in protecting series compensated and adjacent transmission lines are emerging and innovative techniques to deal with such challenges and also to enhance equipment performance continue to be developed

PS-3 Concluding Comments Encouraging to see the high level of co- operation between manufacturers and utilities (evident from the number of joint papers) to solving application problems and also to improve protection equipment It is also apparent that a thorough understanding of the subject is advantageous in order to ensure optimal use of the correct equipment for particular applications

PS-3 Concluding Comments The importance and value added by collaboration through international bodies and working groups should not be underestimated