Estimation of Fault Resistance from Fault Recording Data. Daniel Wong & Michael Tong 2014-November-5

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1 Estimation of Fault Resistance from Fault Recording Data Daniel Wong & Michael Tong 2014-November-5

2 Agenda Project Background & Introduction Fault Resistance & Effect Estimation Algorithm Estimation Results Conclusion

Project Background About AltaLink Canada s only fully independent transmission company Own and operate more than half of Alberta s Transmission Grid Serve 85% of Alberta population

3 Project Background About AltaLink Canada s only fully independent transmission company Own and operate more than half of Alberta s Transmission Grid Serve 85% of Alberta population Interconnections to BC, Saskatchewan and Montana (US) 12,000 km transmission lines 69kV to 500kV 300 substations More than 20,000 protection relays Own and operate a telecommunication (in-house) system

4 Project Background Line Protection Coverage Impedance Protection - one of the widely used line protections Impedance relay responds to Voltage and Current Line impedance contains reactance and resistance Ground fault impedance contains line impedance and ground fault resistance For correct relay operation, relay setting needs to coverage ground fault resistance The question is how much resistance to cover

5 Project Background AltaLink relay setting guidelines (Pre December 2004) AltaLink in-house guideline (up to December 2004) For transmission lines, impedance protection were applied most of the time For zone 1 impedance setting, it needs to cover 5 Ohms Based on actual operating experience, line protection performance was good No problem was identified with the 5 Ohms coverage

Standards: Effective: December 1, 2004 Valid for

6 Project Background AESO Protection Standard Alberta Interconnected Electric System Protection Standards: Effective: December 1, 2004 Valid for 5 years Expired: December 1, 2009 Document Size: 65 pages

7 Project Background AESO Protection Standard Section 3.6 on Fault Types Protection applied to the Alberta Interconnected Electric System must be capable of detecting: Single line to ground fault with 20 Ohms (tower footing plus arc) impedance Phase to phase to ground fault with 20 Ohms (tower footing plus arc) impedance

8 Project Background ISO (AESO) Rules ISO Rules Section Interconnected Electric System Protection Requirements: Draft rules posted on 2012 August 15 for consultation Final rules posted on 2012 December 31 Effective: 2012 December 31 Expiry: No date declared yet Document size: 12 pages

9 Project Background ISO (AESO) Rules - Section Interconnected Electric System Protection Requirements Ground Fault Resistance Coverage: Single line-to-ground fault with impedance up to 5 Ohms Phase-to-phase-to-ground fault with impedance up to 5 Ohms

10 Project Background Based on protection guidelines, standards and rules, requirements on ground fault resistance coverage changes from 5 to 20 and back to 5 Ohms again No improvement or deterioration in protection performance was observed with these changes No study has been carried out to determine the magnitude of ground fault resistance in the AltaLink system In mid 2012, a study project was initiated with University of Alberta

11 Project Introduction Alberta Power Industry Consortium (APIC) Project (Report No. 2013A-1) Develop an algorithm to estimate the fault resistances from fault data recorded and verify the algorithm through simulation and experimental studies Apply the algorithm to a large number of fault cases with COMTRADE fault files in single phase to ground faults on 2- terminal lines Identify the typical value of the ground fault resistance in AltaLink system in order to assess the Protection Setting Guidelines Department of E&C Engineering, University of Alberta P&C Engineering and System Operations, AltaLink

Fault Resistance Single Phase to Ground Fault: Electric arc:

current/length Value is variable during the fault Tower

Value is stable during the fault Objects in the fault path:

12 Fault Resistance Single Phase to Ground Fault: Electric arc: Traditionally considered as a resistance Dependent on the arc current/length Value is variable during the fault Tower grounding: Mainly resistive Not dependent on the fault current Value is stable during the fault Objects in the fault path: Usually considered mainly resistive Might be zero or very high Value is unpredictable

13 Fault Resistance Effect Homogeneous System X ZL 1 R f Z (apparent impedance) R

14 Fault Resistance Effect Non-Homogeneous System X ZL 1 ZL X 1 Z(apparent impedance) Z(apparent impedance) R R Overreach Underreach

15 Estimation Algorithm Two stages: Stage 1: Fault location estimation Stage 2: Fault resistance estimation V S mz L F 1 m ZL V R I S I R Relay R F Relay

16 Estimation Algorithm S-End R-End V 1S S V 1R S I 1S I 1R Z 1S mz 1L (1-m)Z 1L Z 1R I 2S + Z 2S mz 2L (1-m)Z 2L Z 2R - V 2F I 2R I 0S I 0R Z 0S mz 0L (1-m)Z 0L Z 0R 3R F I F

17 Estimation Algorithm Stage 1 Fault Location Estimation Two-Ended Negative-Sequence Impedance Method Negate the effect of pre-fault load and fault resistance, zerosequence mutual impedance. No source are involved, calculation is based on Magnitude. Data alignment is not required. I 2S + Z 2S mz 2L (1-m)Z 2L Z 2R - V 2F I 2R 1 V I Z mz 2F 2S 2S 2L V I Z m Z 2F 2R 2R 2L

18 Estimation Algorithm Stage 2 Fault Resistance Estimation V S mz L F 1 m ZL V R I S I R Relay R F Relay For an A-G fault, Voltage and current at end S: V mz I k I R AS L AS r F F I

92% of the faults on the studied lines have a fault resistance of less

19 Estimation Results 54 fault cases in AltaLink 240KV and 138KV transmission system. 92% of the faults on the studied lines have a fault resistance of less than 5Ω Average/Median value of the fault resistance in 240KV system < Average/Median value of the fault resistance in 138KV system

20 May-07 Jul-09 Jul-09 Sep-09 Mar-10 Apr-10 May-10 Jun-10 Aug-10 Aug-10 Jan-11 Apr-11 May-11 May-11 May-11 Jul-11 Jul-11 Jul-11 Aug-11 Aug-11 Aug-11 Sep-11 Sep-11 Apr-12 Apr-12 Sep-12 May-13 Feb-08 Mar-08 Jul-08 Aug-08 Mar-09 Sep-09 Jul-10 Sep-10 Feb-11 Apr-11 May-11 May-11 May-11 Jul-11 Jul-11 Apr-12 May-12 Aug-12 Aug-12 Aug-12 Aug-12 Oct-12 Nov-12 Feb-13 Mar-13 Jun-13 Aug-13 Estimation Results (All Fault Cases) KV Line Fault Resistance Level (All Fault Cases) KV Line Fault Resistance Level (All Fault Cases) Estimated Value (Ω) Median Value ( 0.76) Average Value (1.31) Estimated Value (Ω) Median Value (2.33) Average Value (2.84)

21 May-07 Jul-09 Sep-09 Mar-10 Apr-10 May-10 Jun-10 Aug-10 Aug-10 Jan-11 Apr-11 May-11 May-11 May-11 Jul-11 Jul-11 Jul-11 Aug-11 Aug-11 Aug-11 Sep-11 Sep-11 Apr-12 Apr-12 Sep-12 May-13 Feb-08 Mar-08 Jul-08 Aug-08 Mar-09 Sep-09 Jul-10 Sep-10 Feb-11 Apr-11 May-11 May-11 May-11 Jul-11 Jul-11 Apr-12 May-12 Aug-12 Aug-12 Aug-12 Aug-12 Oct-12 Nov-12 Feb-13 Jun-13 Aug-13 Estimation Results (Excluding Outlier) 8 240KV Line Fault Resistance Level (Excluding Outlier) 8 138KV Line Fault Resistance Level (Excluding Outlier) Estimated Value (Ω) Median Value ( 0.72) Average Value (0.87) Estimated Value (Ω) Median Value (2.17) Average Value (2.31)

22 Estimation Results (Pie Chart) Fault Resistance Level (All Fault Cases) Fault Resistance Level (Excluding Outliers) > 5 Ohm 8% > 5 Ohm 4% 2 ~ 5 Ohm 24% 2 ~ 5 Ohm 25% < 2 Ohm 68% < 2 Ohm 71%

23 unknown Tractor unknown lightning Contamination Bird Nest Bird Nest Bird Nest unknown Lightning unknown Lightning CVT failure Lightning Conductor Cross-arm Cross-arm Lightning Contamination Conductor Lightning Conductor Contamination Gravel Truck Lightning Lightning Dump Truck Cross-arm Weather unknown Lightning Contamination unknown unknown unknown Icing unknown Shield Wire Estimation Results (Ω vs. Cause) KV Line Fault Resistance Level (All Fault Cases) KV Line Fault Resistance Level (All Fault Cases) Estimated Value (Ω) Median Value ( 0.76) Average Value (1.31) Estimated Value (Ω) Median Value (2.33) Average Value (2.84)

24 Protection Setting Guidelines Existing Protection Setting Guidelines for Line Protection.. Impedance Zone 1: Generally zone 1 is the zone set to underreach the end of the protected line. Zone 1 reach shall be set to 85% of the actual impedance of the protected line with no intentional tripping delay. Mutual coupling with parallel lines causes overreaching for some faults; the zone 1 reach may be reduced to no less than 60% of the line impedance to allow the two opposite zone 1 reaches to overlap with 15% margin, provided a ground fault with 5 ohms resistance still produces high-speed operation...

25 ISO Rules Part 500 Facilities Section Interconnected Electric System Protection Requirements.. Bulk Transmission Line Ground Fault Resistance Coverage 15 If a bulk transmission line experiences a fault of the following type, then each of the two (2) protection systems for the bulk transmission line must initiate isolation of the fault: (a) single line-to-ground, with a minimum impedance of five (5) ohms; or (b) phase-to-phase-to-ground with a minimum impedance of five (5) ohms....

26 Conclusion (Project Specifics) An off-line method is proposed for estimating the fault resistance in single phase-to-ground faults. The method eliminates the need to synchronize the fault data. The developed program makes it possible to estimate the fault resistances in a large number of fault cases, and to obtain a statistical picture of typical fault resistance values. More than 50 fault events are studied and the estimation result aligns with AltaLink Protection Setting Practice.

27 Conclusion (Application Specific) With the outliers excluded, 96% of the recorded ground fault resistances were less than 5 Ohms The 5 Ohms requirement for ground fault resistance coverage, as stated in the ISO (AESO) Rules is appropriate AltaLink provides 5 Ohms ground fault resistance coverage in full compliance with Rules 502.3

28 Questions

DOUBLE-ENDED FAULT LOCATORS

The InterNational Electrical Testing Association Journal FEATURE END-TO-END TESTING OF DOUBLE-ENDED FAULT LOCATORS BY STEVE TURNER, Beckwith Electric Company, Inc.. www.netaworld.org FOR HIGH VOLTAGE,