NERC System Protection and Control Task Force. Presented to the Western Protective Relay Conference Spokane, Washington October 20, 2004

Transcription

1 NERC System Protection and Control Task Force Presented to the Western Protective Relay Conference Spokane, Washington October 20, 2004

2 Outline History Recommendations SPCTF Organization SPCTF Scope Comments from NERC Aug 14, 2003 Blackout Investigation Team Bob Stuart SPCTF Clarification of Ratings Bill Kennedy SPCTF Recommendations to NERC PC SPCTF Exception Criteria Jon Daume, Skip Williams Q&A - Panel 2

3 History WECC Blackouts 1996 Distance Relays were found to contribute January 1997 IEEE Computer Applications in Power Article by Carson Taylor and Dennis Erickson o Responses by Charles Henville and Charles Rogers in April 1997 Computer Applications in Power (letters to editor) August 14, 2003 Eastern Interconnection Blackouts U.S. Canada Power System Outage Task Force Reports on 11/19/03 and 4/4/04 NERC Investigation BOT Approved Recommendations on 2/10/04 July 13, 2004 NERC Technical Analysis Report ECAR Investigation Report on 2/16/04 3

4 History (Continued) All investigations into August 14, 2003 blackout found that Distance Relays tripping for non-fault conditions contributed to the blackout Much Criticism for Not Addressing Distance Relays after earlier blackouts NERC Planning Committee Formed a task force to address Relaying Issues relating to August 14, 2003 blackout SPCTF Scope was Approved by NERC on 3/25/04 SPCTF Staffed by NERC on 5/14/04 4

5 Recommendations NERC Recommendation 8a US Canada Power System Outage Task Force Recommendation 21a 5

6 SPCTF Organization Charles Rogers Consumers Energy Chairman (ECAR) Mark Carpenter TXU Electric Delivery Vice Chairman (ERCOT) John Mulhausen Florida Power and Light (FRCC) Al Darlington Tampa Electric (retired) (FRCC Alternate) Joe Burdis PJM Interconnection (MAAC) Bill Miller Excelon (MAIN) Deven Bahn WAPA (MAPP) Phil Tatro National Grid (NPCC) Phil Winston Georgia Power (SERC) Skip Williams AEP (ECAR Alternate) Fred Ipok Springfield, MO. SPP Dave Angell Idaho Power (WECC) Baj Agrawal APS (WECC Alternate) Jon Daume BPA (WECC Alternate) John Ciufo Hydro One (Canada - Eastern) Bill Kennedy Alberta Electric System Operator (Canada - Western) Jim Ingleson NYISO (ISO/RTO) Evan Sage PEPCO (IOU) Gary Kobet TVA (Federal) Keith Orsted American Transmission Company (TDU) Robert Stuart NEXANT, PGE (retired) (NERC Investigation Team) Tom Weidman Commonwealth Edison (retired) (NERC Investigation Team) Bob Cummings NERC Staff 6

7 SPCTF Scope Highlights Review and Report on Pros and Cons of Zone-3 Relays on Transmission Systems Review Zone-3 Relay Settings to Avoid Tripping on Load Review Requests for Exception and Report to PC Merits and Deficiencies of UVLS Review Region Evaluations of UVLS Feasibility and Benefits Review NERC Planning Standard III and Recommend Revisions as Appropriate General Review of Protection System Design to Improve Protection of System and Prevent/Mitigate Cascading Failures 7

8 SPCTF Activities To Date Clarified Definition of Rating Defined Zone 3 Further Defined Zone 3 Schedule and Assigned Major Roles to Regions Defined Temporary Exceptions and Technical Exceptions Developed draft Technical Exception Criteria Developed Technical Exception Reporting Form 8

9 NERC Investigation Team Bob Stuart NERC Investigation Team 9

10 NERC Investigation Team Zone 3 relays contributed to blackout Sammis Star 345 kv 16:05:57 escalated cascade East Lima Fostoria Central 345 kv trip accelerated cascade In total, 14 lines tripped by distance relay due to load encroachment 10

11 NERC Investigation Team Sammis Star tripped at 16:05:57 by Zone 3 Load Encroachment 120% emergency rating; 0.96 p.u. voltage (Sammis end); 27 degree line angle Zone 3 relay set for 200% of line to protect transformer 1500 MW of load dropped prior to line relaying would have contained disturbance to Cleveland 11

12 NERC Investigation Team Factors taken into consideration WECC Guidelines degree power factor angle p.u. voltage - margin recommended based on power flow studies Establish capability to ride thru severe disturbances - Give operators 10 to 15 minutes to drop load or reconfigure system Discussed with investigation team 12

13 NERC Investigation Team Conductor short term emergency ratings - 15 minute ratings based on more aggressive conditions - Achievable over 50% of time - normal ratings at 75% of line rating 10 to 15 minutes to reach 100 degrees C Assumed 15 to 25 % relay margin - CT and PT error - Relay error 15 to 25% margin above short term emergency rating will still allow small margin for 150% of summer emergency ratings 13

14 NERC Investigation Team Calculated relay settings for various lengths of lines Determined that line lengths above 75 miles would be difficult to set zone 3 relays assuming 150% setting Make relays less sensitive to load encroachment - Increasing maximum torque angle to 90 degrees - Activating load encroachment feature on modern relays - Installing blinders Asked two large utilities (represented on Investigation Team) to review proposed policy very small percentage had some mitigation to do may not be representative Policy intended to drive stake in ground more specific guidelines would have to be generated later 14

15 SPCTF Recommendations Bill Kennedy - AESO 15

16 SPCTF Clarification on Ratings NERC Recommendation 8a footnote states emergency ampere rating NERC PC Minutes March 24 suggests long time summer emergency ampere rating SPCTF Clarification (June 18) Highest seasonal ampere circuit rating that most closely approximates a 4-hour rating considering the lowest ampere rated device in the line 16

17 SPCTF Recommendations TPSO Transmission Protection System Owner Current Process to Address Only Zone-3 Relays Zone-3 Relays Defined As Remote Backup Relays (IEEE C Clause ) Inject Regions Into Zone-3 Process Build on Their Natural Relationships With the TPSO s TPSOs to Respond to Regions by Dates Established in NERC Recommendation 8a Regions to Assure That All TPSOs Have Responded and Respond to NERC 1 Month Later 17

18 SPCTF Recommendations (Continued) Establish Two Classes of Exception Temporary and Technical Temporary Exceptions to Request Delayed Schedule for Workforce or Construction Clearance Issues Must Include Proposed Schedule Technical Exceptions to Address Conditions Where Thermal Limits Are Not the Practical Limiting Condition SPCTF Developing Technical Exception Criteria SPCTF to Review All Exception Requests and Report to PC Denied Requests Must Be Mitigated in 1 Year 18

19 SPCTF Recommendations (Continued) All Other Load-responsive Relays to Be Reviewed and Addressed on a Schedule to Be Developed by SPCTF Exceptions to Be Reviewed by Regions Regions to Identify Critical Lines 115kv and Above for Inclusion in Review (Joint TF Recommendation 21a) All Recommendations were Approved by NERC PC on July 15,

20 Implementation Timeline for NERC Recommendation 8a Activities 12/31/2004 TPSOs Submit to Regions: - Certification of conformance to loadability - Violation mitigation (before 12/31/05) plans - Applications for exceptions 12/31/2005 TPSOs Submit to Regions: - Certification of full conformance - Implementation dates for outstanding violations 9/30/2004 TPSOs report to Regions on Zone 3 reviews 2/10/2004-9/30/2004 TPSOs review Zone 3 relays for conformance 9/30/ /31/2004 TPSOs mitigate violations 1/1/ /31/2005 TPSOs mitigate violations 2/10/2004 NERC Rec. 8A Issued by Board Today 10/31/2004 Regions Report TPSO completion of 9/30 review to SPCTF 1/31/2005 Regions report TPSO responses of 12/31/04 to SPCTF 2/1/2006 Regions report TPSO responses of 12/31/05 to SPCTF 20

21 SPCTF Exception Criteria Temporary Exceptions Technical Exceptions Realistic Circuit Ratings Achieve Minimum Acceptable Protection Network Topology Transmission System Must be Adequately Protected, and Distance Relaying Must also allow for Maximum Practical Load Flow Distance Relaying Must Not Contribute to Cascading Outages 21

22 Ratings and Technical Exceptions NERC Recommendation 8a refers to circuit thermal ratings SPCTF Clarified to highest seasonal 4-hour rating of most limiting circuit element Thermal ratings may not represent practical circuit ratings Technical Exceptions attempt to address the other practical circuit capabilities 22

23 Temporary Exceptions Permit delayed implementation because of workforce issues, construction outage constraints, or availability of replacement equipment Not intended to provide for budget relief TPSO must do all possible to mitigate with Existing Equipment Must Include Proposed Schedule for Mitigation 23

24 Technical Exceptions Twelve Individual Technical Exception Criteria Establishes lower margins for shorter-term circuit ratings (1) Address other system limitations that present more realistic actual system rating criteria (5) Establish ratings based on minimally-adequate protection (2) Natural system limitations due to topology (4) 24

25 Technical Exception #1 Utilize the 15-Minute Rating of the Transmission Line The tripping relay should not operate at or below 115% of the 15-minute winter emergency rating Assuming: 0.85 per unit voltage line phase angle of 30 degrees 25

26 Maximum Power Transfer Diagram Sending X S = 0 X L X R = 0 Receiving E S = 1.0 PU V S P R = V S V R X sinδ L V R E R = 1.0 PU The maximum real power that a transmission line can transfer occurs when the voltage angle across the line reaches 90º. 26

27 Maximum Power Transfer Capability 345 kv (2 X 1272 ACSR) Line Loadability Apparent Power (MVA) & St. Clair (MW) St. Clair Curve MW St. Clair MVA S 1.5xWE Ss (Vs=1 δ=90 ) Line Length (miles) 27

28 Derivation of the Exception Equation V P = P = V S 2 X L V R X sinδ L VS VS VR Q = cos X X ( o δ ) The real and reactive currents are equal at maximum power transfer Q = V L 2 X L 2 L 28 I total = 2 I real I total 2 V = 3 X L

29 Technical Exception # 2, 3 and 4 The protective relays only need to accommodate the power transfer capability of a transmission line #2 Line X only, 1.00 p.u. V Recertify when line is changed #3 Line and breaker interrupter rating, 1.05 p.u. V Recertify when breaker is underrated or changed #4 Line and actual source impedance, 1.05 p.u. V Recertify annually 29

30 Technical Exception #5 Special Considerations for Series- Compensated Lines Tripping relay should not operate at or below the greater of: times the highest emergency rating of the series capacitor 2. I total (calculated under Exception 2, 3, or 4 using full line inductive reactance) assuming 0.85 per unit voltage line phase angle of 30º 30

31 Technical Exceptions Part 2 Skip Williams AEP 31

32 Technical Exception #6 Weak Source Systems The tripping relay should not operate at or below 1.15 times I = I max Assuming: fault 0.85 per unit voltage at a load phase angle of 30 degrees where I max is the maximum end of line three-phase fault current magnitude. 32

33 Technical Exception 6 - Drawing OPEN FAULT TRANSMISSION SYSTEM R LOAD CENTER Weak Source Systems 33

34 Technical Exception #7 Long Line Relay Loadability Long line relay loadability can be adjusted as long as ALL of the following conditions are met: 1. Most sensitive tripping relay set 125% of total line impedance 2. MTA set as close to 90 degrees (sanctioned by manufacturer) 34

35 Technical Exception #7 (cont.) 3. Short-term emergency rating (I emergency ) of line is equal to or less than: Vrelay cos( MTA Θline) I emergency = Zline cos( MTA 30 ) Where V is the nominal line-to-line voltage and Z line is the impedance of the line in ohms 4. I emergency used in all planning and operational modeling for STE Rating (15-min. or most closely approx. 15-min. rating) 35

36 Technical Exception #7 (cont.) 5. No current or subsequent planning contingency analyses identify any conditions where the recoverable flow is greater than I emergency 6. Transmission Operators take immediate remedial steps, including dropping load, if current reaches I emergency If any of these conditions are violated, then the condition must be fully mitigated to avoid the loadability issue 36

37 Technical Exception 7 - Drawing X Z RELAY 1.25 Z LINE Z LINE MTA 30 0 R Z RELAY 30 LINE Long Line Loadability 37

38 Technical Exception 8 Three (or more) Terminal Lines Similar to Exception 7, except considers apparent impedance to the most distant line terminal, instead of simply considering line impedance Includes lines with significant taps 38

39 Technical Exception #9 Generation Remote to Load The tripping relay should not operate for 1.15 times the maximum current, representing twice the aggregate generator MVA capability, assuming 0.85 per unit voltage line phase angle of 30 degrees 39

40 Technical Exception 9 - Drawings GENERATION CENTER LOAD BUS A R R OPEN OPEN LOAD BUS B LOAD BUS C LOAD CENTER R Generation Connected to System Multiple Lines 40

41 Technical Exception #10 Load Remote to Generation The tripping relay should not operate for 1.15 times the maximum current flow as calculated by the TPSO assuming 0.85 per unit voltage line phase angle of 30 degrees 41

42 Technical Exception 10 - Drawing GENERATION CENTER LOAD BUS A R R LOAD BUS B LOAD BUS C LOAD CENTER R Load Remote to Generation 42

43 Technical Exception #11 Remote Cohesive Load Center The tripping relay should not operate for 1.15 times the maximum current flow as calculated by the transmission owner assuming 0.85 per unit voltage a line phase angle of 30 degrees 43

44 Technical Exception 11 - Drawing TRANSMISSION SYSTEM R R LOAD CENTER R Remote Cohesive Load Center 44

45 Technical Exception #12 Cohesive Load Center Remote to Transmission System The Tripping relay should not operate for 1.15 times the maximum current flow as calculated by the TPSO assuming 0.85 per unit voltage line phase angle of 30 degrees 45

46 Technical Exception 12 - Drawing TRANSMISSION SYSTEM R R LOAD CENTER R Cohesive Load Center Remote to Transmissions System 46

47 Wrapup and Conclusions Dave Angell 47

48 Some Possible Mitigation Methods Must Adequately Protect System Disable Unnecessary Protective Elements Increase Distance Relay Maximum Torque Angle Utilize load-tolerant relay characteristics Utilize Transfer Trip for Remote Backup Transmission System modifications to Facilitate Protection Others? 48

49 SPCTF Next Distance Relay Activities All other load responsive relays (230 kv and above, and lower voltage level critical facilities) must also not limit practical loading capability. Includes Zone 2 relays, pilot-scheme relays, and overcurrent relays DCB Carrier Schemes can improperly operate on through load if lines are consuming significant real and reactive power Will have a different schedule for analysis, reporting, and mitigation Must adequately protect electrical system! 49

50 SPCTF Documents Approved SPCTF Documents may be found on the NERC web site at: Official Reports on the August 14, 2003 Blackout may be found on the NERC web site at: 50

51 SPCTF Contacts For detailed questions or suggestions, please contact Bob Cummings Charles Rogers Mark Carpenter Any other SPCTF member We Need everyone s help for us to do the best possible job! 51

52 NERC SPCTF Q&A Panel Members All Available SPCTF Members 52