Cascade-Based Planning Analysis. Robert W. Cummings NERC Senior Director of Engineering and Reliability Initiatives

Transcription

1 1 Cascade-Based Planning Analysis Robert W. Cummings NERC Senior Director of Engineering and Reliability Initiatives

2 WHAT SHOULD BE STUDIED 2

3 3 Tenets of Cascading Analysis Why do it? Learn from History What is a credible combinations of events? What should I think might get involved? Be imaginative Murphy is! Be a Student of the System!! Constantly observe how your system behaves normally and when under stress How does your system interact with the rest of the Interconnection? Practice simulating actual events Good for model validation Helps avoid complacency

4 4 Some Trends in Event Analysis 1. Protection system misoperations (39) 2. Unexpected Gen. Turbine Control Action (33) 3. Transmission equipment failures (18) (most initiating) 4. Voltage sensitivity of gen. aux. power systems (13) 5. Human Error (12) 6. Near-term load forecasting error (6) 7. Wiring errors (incidental) (5) 8. Relay loadability (5) 9. Inter-area oscillations (5) 10. SPS & RAS Misoperations (5)

5 5 Two Top Disturbance Elements 33 Unexpected generator turbine control actions 29 in 8 events 2 units CAUSAL in a system separation event 13 Voltage and/or frequency sensitivity of generation auxiliary power systems (not included above) or plant / Unit Digital Control Systems Problem: THESE BEHAVIORS ARE NOT MODELED OR STUDIED Boiler and Turbine controls are not modeled Understand roll of controls action Power-Load Unbalance (PLU) Typical dynamic analysis only analyzing t = 0 to t = 20 seconds control actions can go well beyond that What about fuel system controls?

6 6 Planning a Cascading Study Be imaginative! You may have to design study methodology to mimic past disturbances to see if the system is still susceptible Think in bus-breaker mode Bus-line model thinking will not get you there Break-to-breaker study needed to analyze protection system misoperations Know your protection system configurations Directional distance, reach, differentials, breaker failure local or remote, Remedial Action Schemes, transfer tripping, etc. Expect the analysis to piece-wise slices of time to mimic the developing overloads or potential voltage collapses

7 7 Planning a Cascading Study (cont.) What parameters do you have to monitor within the study to tell you what would be the next step of the cascade? Look for overloaded lines How overloaded are they? Voltages below 0.9 per unit How low? Results of one run flow into another Reactive flow into both ends of a line? Think about controls!! Inverter controls play a part too! Behavior during protracted faults breaker failure (to operate) emulation SLG faults transition to multi-phase in cycles Longer faults evolve into 3-phase faults

8 8 Planning a Cascading Study (cont.) Protracted faults mean protracted low voltages UVLS schemes? Inverter behavior during low voltages Inverter blocking current injection? Inverter tripping? Know your loads! Know your station load composition residential, commercial, industrial, etc. Helps characterize load behavior under abnormal conditions Loads with high-quality power requirements may leave the system Voltage-sensitive or frequency sensitive loads must be monitored during the study

9 9 Study Practices Cardinal Rule of forensic event analysis Everything happens for a reason!! There is no sympathy in the power system Think like a protection system or plant control system What the heck did it see?? Why did it react the way it did? Take advantage of all available disturbance monitoring data (PRC-002) Leave no questions unanswered Don t be myopic in the scope of your analysis! Examine the Interconnection to ensure there were no wider area impacts Timing is everything! Creating a detailed sequence of events is crucial!

10 10 Study Practices (Continued) Cascading typically starts slow and progresses as multiple things go wrong Know the cascade players Triggering event lightning arrestor failure Causal events Breaker fails to operate protection system failure Contributory events Protection system miscoordination widens impact Coincidental events It was a dark and stormy night Resultant events fault progressed from single-phase to multi-phase

11 11 EXAMPLE 1 NORTHEAST BLACKOUT AUGUST 14, 2003

12 Blackout Signature MW/MVAr 4000 MW kv kv MVAr :10:38 16:10:40 16:10:42 16:10:44 16:10:46 16:10:48 Time - EDT

13 13 Major Path to Cleveland Blocked ONTARIO 4:08:59-4:09:07 PM

14 8 Generation Trips ONTARIO

15 9 Cascade Moves into Michigan 4:10:36 PM

16 Power Transfers Shift 4:10:38.6 PM 10

17 11 Northeast Island Separates from EI North of Lake Superior 4:10:43 4:10:45 PM

18 12 End of the Cascade Area affected by blackout Service maintained in isolated pockets

19 Frequency (Hz) Start of split between East and West MI Detroit, Cleveland separated from W. MI. Cleveland cut off from PA NY separates from PA Cleveland separates from Toledo, islands 1630 MW Detroit generation trips NY separates from NJ NY and New England separate Split complete between East and West NY Ontario splits from West NY Ontario reconnects with West NY Power Flows (MW) 13 5,000 4,000 3,000 2,000 1, ,000-2, Blackout Analysis 16:10:36 16:10:38 16:10: :10: :10:48 16:10:50 16:10:56 16:10: :10:49 16:10: :10:42 New York into Ontario Ontario into Michigan New York into New England PJM into New York -3,000 16:10:30 16:10:40 Time 16:10:50 16:11:00 16:10:30 to 16:11: NY-West Lambton ONT-MI NY-East 57 16:10:30 16:10:40 Time 16:10:50 16:11:00

20 % of Normal Ratings (Amps) Dale-W.Can 138 kv W.Ak 138 kv Bkr Failure Cham-W.Ak 138 kv E.Lima-N.Fin 138 kv CantC Xfmr W.Ak-PV Q kv Babb-W.Ak 138 kv E.Lima-N.Lib 138 kv Clov-Torrey 138 kv Star-S.Cant 345 kv Hanna-Jun 345 kv Hard-Chamb 345 kv Blackout Simulations 3 Months to Build Sammis-Star 345 kv 100 CantC-Tidd 345 kv Star-S.Cant 345 kv Hanna-Jun 345 kv Hard-Chamb 345 kv 0 Outages

21 Some Key Elements of the Cascade Vegetation management Relay loadability Miscoordination of generator controls and system protection Generator underfrequency protection and under / over speed controls not coordinated Pole Slipping UFLS failures Constrained by extreme undervoltage Time delays too long 21

22 22 What to look for in the study Slow cascading not all cascades happen at dynamic speeds Slow, progressive Voltage collapse Increasing overloads of key elements over time Loading above Surge Impedance Limits (SIL) Reactive power entering the line from both ends Excessive bus angles across transmission lines Potential for parts of the system separating by out-of-step conditions If it trips can you reclose it?? Doubtful for angles above 45 degrees

23 Relative Phase Angle 16 Angular Separation Analysis :05:00 15:32:00 15:44:00 15:51:00 16:05:00 16:06:01 16:09:05 16:10:38 Reference: Browns Ferry Normal Angle ~ -25º Time (EDT) Cleveland West MI 23

24 24 16:05:50 to 16:08:52 Western MI Sammis - Star NJ Detroit Muskingum Ohio Central - Galion East Lima Fostoria Central 15 Degrees NY Ontario Cleveland 24

25 18 Detroit out of Synch 16:08:50 to 16:10:50 Western MI NY NJ 40 Degrees NY-PJM Separation Cleveland Separation Cleveland Ontario 25

26 26 EXAMPLE2 FLORIDA SYSTEM DISTURBANCE FEBRUARY 26, 2008

27 27 Event Overview Delayed clearing of 138 kv SLG fault progressed to a 1.7 second 3-Ø fault Loss of 1,350 MW load near fault Loss of 2,500 MW of generation near fault Loss of 2,300 MW more load by UFLS program Loss of 1,800 MW more generation across the Region Oscillatory effects across interconnection

28 30 Key Elements of Cascade Protection system turned off Single Ø fault progressed to three Ø fault 1.7 seconds Nuclear units tripped on undervoltage as designed Eight turbines unexpected trips; auxiliary bus voltage protection rate of frequency change -- burner lean blowout phenomenon Proper UFLS action prevented system separation Inter-area oscillations 1,000 MW swings in TVA 500 kv system 600 MW swings in New England 345 kv system 12 kv swings on Ontario 230 kv system

29 29 Florida UFLS Activation FRCC RC Visibility Event Summary Impact contained within FRCC Majority of load restored within 2 hrs. No major equipment damage reported No thermal O/L 2 Nuclear units (tripped as designed) Generation Trips Actuation of UFLS FRCC RC Footprint Location of 138 kv 3θ fault

30 29 Interconnection-wide Impact Turkey Point (FPL) Calloway / Rush Island TVA Dorsey (MH)

31 31 What to look for in the study Localized voltage collapse Low voltages on generators Motor controllers often drop out for voltages below 0.87 per unit Potential inter-area oscillations Excessive bus angles across transmission lines Potential for parts of the system separating by out-of-step conditions If it trips can you reclose it?? Doubtful for angles above 45 degrees

32 32 EXAMPLE 3 PACIFIC SOUTHWEST DISTURBANCE SEPTEMBER 8, 2011

33 CAISO Freq/ACE MST From RA Tool CISO Freq/ACE MST

34 1-Min. CAISO Freq MST From RA Tool

35 System Separation & SONGS Trip Loss of SDGE Loss of San Onofre Gen. Load From RA Tool

36 Initial FNet FDR Angular Plot AZ-NM-CO California

37 FNET FDR Locations

38 Event A

39 Event A Detail

40 Event B

41 Event C

42 Event D

43 What we learned with FNET The frequency shows four main events A. The initial separation around 22:27:39 (UTC), resulting in a slow frequency dip of about -30 mhz over about 25 seconds B. A frequency ramp beginning around 22:32:10 increasing frequency +30 mhz over about 15 seconds C. A frequency drop around 22:37:55 of over -40 mhz (B-A) over about 12 seconds D. A frequency jump around 22:38:21 of over +150 mhz (C-A) in less than 5 seconds, settling at around +80 mhz (B-A) in about 20 seconds

44 Components of the Outage Over 30 major element operations over the course of 11 minutes Line and transformer trips Generator trips and runback Load shedding Over 50 additional minor operations such as capacitor and reactor switching Over 6 GB of data of different qualities and resolution Operator logs, PI historian, SCADA, PMU, DFR, relay records

45 45 What to look for in the study Think like a phasor measurement unit (PMU) But don t be fooled by phase-jumps at inception of a fault, clearing of a fault, or significant reactive switching Think Multi- dimensionally! Don t fixate on single reading Frequency, voltage, current, time multi-dimensional plots Potential for inter-area oscillations Recognize tripping of various system elements Line trip, Transformer trip, Load trip Excessive bus angles across transmission lines If it trips can you reclose it?? Doubtful for angles above 45 degrees

46 Phase 1 Pre-Disturbance Hot, shoulder season day; some generation and transmission outages High loading on some key facilities: H-NG at 78% of normal rating; CV transformers at 83% 44 minutes before loss of H-NG, IID s RTCA results showed loss of CV-1 transformer would load CV-2 transformer above its relay trip point 15:27:39: APS technician skipped a critical step in isolating the series capacitor bank at North Gila substation; H-NG trips

47 Phase 2 Trip of H-NG 500 kv H-NG 500 kv trips at 15:27:39 15:27:39 15:28:16 APS tells WECC RC line expected to be restored quickly H-NG flow redistributes: 77% to SCE-SDGE (Path 44); remainder to IID, and WALC CV transformers immediately overloaded above relay settings Path 44 at 5,900 amps; 8,000 amp limit on SONGS separation scheme

48 Initiating Event Voltage Divergence Hassayampa North Gila 500 kv Trip Series Capacitor Bypass Switch Arcs Over

49 Hass. N. Gila 500 kv Line Trip South of SONGS Current CCM Unit 1 generator trip Hassyampa N. Gila 500 kv line trip

50 15:28:16 15:32:10 Phase 3 Trip of CV Transformers 15:28:16 CV-2 and CV-1 230/92kV transformers trip on overload relays Severe low voltage in WALC 161 kv system Loading on Path 44 increases to 6,700 amps

51 Coachella Valley Transf. Trip South of SONGS Current Coachella Valley 230/92 kv transformers trip

52 Phase 4 Ramon Transformer Trip 15:32:10 Ramon 230/92kV transformer trips on overload relay 15:32:10 15:35:40 15:32:13 Blythe-Niland 161kV line trips 15:32:15 Niland CV 161kV line trips IID undervoltage load shedding; loss of generation and 92 kv transmission lines Severe low voltage in WALC 161 kv system Loading on Path 44 increases to 7,800 amps; settles at 7,200 amps

53 Ramon Transformer Trip South of SONGS Current Voltage collapse in pocket, followed by load tripping Multiple line, generator and load trips Ramon 230/92 kv transformer trip

54 Voltage in Northern IID 92 kv System Over-Voltage Trip of 92 kv System Capacitors Ramon 230/92 kv Transformer Trip Trip of Over 400 MW in Northern IID 92 kv Load Pocket

55 Blythe 161 kv Voltage Trip of Hassayampa North Gila 500 kv Line El Centro Pilot Knob 161 kv Line Trip Trip of Coachella Valley 230/92 kv Transformers Yucca 161/69 kv Transformers 1 and 2 Trip Ramon 230/92 kv Transformer Trip Trip of Over 400 MW in Northern IID 92 kv Load Pocket

56 Phase 5 Yuma Separates 15:35:40 15:37:55 Yuma AZ Separates from IID and WALC when Gila and Yucca transformers trip Yuma load pocket isolated on single tie to SDG&E Loading on Path 44 increases to 7,400 amps after Gila transformer trip; to 7,800 amps after Yucca transformers and generator trip

57 Yuma Separation South of SONGS Current YCA generating units trip Yucca 161/69 kv transformers trip Pilot Knob 161/92 kv transformers trip Gila 161/69 kv transformers trip

58 15:37:55 Phase 6 High-Speed Cascade El Centro Pilot Knob 161kV line trips; all IID 92 kv system radial from SDG&E via S-Line WALC 161 kv system voltage returns to normal Path 44 exceeds 8,000 amp setting and timer starts

59 Phase 6 High-Speed Cascade South of SONGS Current CLR generating units trip Imperial Valley El Centro 230 kv S line trip SONGS separation El Centro Pilot Knob 161 kv line trip

60 SONGS Separation Frequency Impacts Hz Phase Jump Transient ~ Hz System Zenith (Point C) ~ Hz System Response (Value B) Hz Pre-Event (Value A) :38: :38: :38: :38: :38: :38: :38: :38: :38: Ault (Denver) Mead (Las Vegas) Tesla (Sacramento) Palo Verde Grand Coulee SONGS Recalculated Frequency Devers Recalculated Frequency

61 SONGS separation SONGS Unit 2 GSU trip and transfer of aux load SONGS aux load on startup transformers SONGS generators ring down SONGS Unit 3 GSU trip and transfer of aux load

62 UFLS Operations in the Island

63 Phase 4 Example Two GTs & UVLS CV-Niland UVLS Motor stalling Colmac GT Blythe-Niland

64 Phase 5 Example transformers trip generators trip

65 Phase 6 Example Blythe RAS S line RAS generators A line trip S line RAS generators

66 Devers SVC Output

67 Capacitor Switching capacitor switching candidate signatures location confirmed by comparing voltage

68 Questions? 68