Low SCR Wind Identification and Mitigation. Will Lovelace MIPSYCON 2015 November 11 th, 2015

Transcription

1 Low SCR Wind Identification and Mitigation Will Lovelace MIPSYCON 2015 November 11 th, 2015

2 System Background - Diagram

3 System Background - Diagram

4 System Background - Description MW wind farm on remote 115 kv system 133 GE 1.5 MW Type 3 machines Four control groups 54 mile ACSR (weak) to the south 58 mile T2-477/477 ACSR (strong) to the east Originally two load serving lines networked in 2008 when the wind farm was built

5 System Background - Limits Wind-adjusted ratings Line L1 and L3 Steady State voltage stability limits 120 MW on Line L1 SPS Flow > 120 MVA on line L1 towards S1 Trip 80 MW wind generation at farm

6 System Background - Operating Processes Limit Wind Farm during local 115 kv line switching L1 No limit L2 60 MW L3 60 MW No limits for transient stability during prior outage

7 Composite Short Circuit Ratio (CSCR) CSCR = SCC system P wind SCC system is the 3ph fault MVA at the high-side wind generator transformer equivalent bus with all local and nearby high-side wind generator transformer equivalent buses shorted Local and nearby wind machines disconnected P wind is the total nameplate capacity of all local and nearby wind generation

8 Composite Short Circuit Ratio (CSCR) 0.6 kv 34.5 kv SCC system 115 kv System Intact SCC system = 307 MVA CSCR 1.5 Outage of L2 SCC system = 176 MVA CSCR 0.9

9 Composite Short Circuit Ratio (CSCR) Historically, a CSCR < ~3.0* meant instability Presently a CSCR > ~1.0* could be managed with control changes in some cases MPC s current CSCR interconnection criteria is: CSCR < 3.0* (or applicable manufacturer data) requires further analysis *The above CSCR limits are not prescriptive and CSCR needs to be considered on a case-by-case basis.

10 Event A - 6/7/2011 A. Initial B-phase SLG fault on L2 B. L2 opens after ~2 cyc and wind farm begins to go unstable C. SUB A Zone 1 Phase B-C element asserts after ~2.5 cyc D. L4 opens after ~2 cyc

11 Event A - 6/7/2011 A B C D

12 Event B - 11/28/2011 A. L1 manually opened by MPC Operators and voltage begins to decay B. SUB A & B Zone 1 Phase A-B & B-C elements looking both directions assert after ~4.4 sec C. L2 opens after ~1.5 cyc

13 Event B - 11/28/2011 A B/C B C

14 Wind Farm Instability vs. Distance Relaying The swing briefly (1/4 cyc) tricks the distance element of the SEL 311C into seeing a forward fault Too fast (25 Hz) to be handled with OOS tripping/blocking Option: Introduce a Zone 1 phase distance delay NOTE: Be careful with this so as not to propagate the swing outside the local system

15 Wind Farm Instability vs. Distance Relaying While not intended the operation of the Zone 1 distance element protects the rest of the system by tripping the farm BUT The wind turbine restart procedure is long and complicated due to loss of the grid tie, and the operation of the distance element in every situation is not guaranteed

16 GE Study #1 Identify and Qualify Issues A model of the local system was built in GE s EMTP-type proprietary software Three historical events ran 6/7/ /9/ /28/2011 Model output benchmarked against historical recordings Preliminary recommendations

17 GE Study #1 Modeling/Validation Simulated voltage (p.u.) at Sub B during manual opening of L3 Lighter shaded line is the historical recording. Motor modeling assumptions correct, but other load responses not modeled.

18 GE Study #2 Quantify Issues and Propose Solutions Refine modeling of Study #1 Comprehensive analysis Long-term voltage stability (plant level control) Short-term voltage stability (generator level control) Voltage regulator stability (dq/dv) Fast Dynamics Specific control change recommendations

19 GE Study #2 Voltage Stability P-V and Q-P analysis Long-term (LT) and short-term (ST) Combinations of local outages and contingencies

20 GE Study #2 Voltage Regulator Stability (dq/dv) Practical limit (+/-10% margin) For most conditions, more limiting than voltage stability Hard limit

21 GE Study #2 Limits Note capacitive load has a 10 MW negative effect

22 GE Study #2 Control Change Summary Generator-level control changes Plant-level control changes Operating process changes

23 GE Study #2 Generator level Control Changes Weak grid control changes on ALL turbines Decreased gains in control loop Lower rate of active current change Fast-stop feature enabled on 53 turbines Detects a large increase in system impedance between time-steps and trips turbine Turbines automatically restart after 2 minutes

24 GE Study #2 Plant Level Control Changes Reduce response time of voltage regulator Enable line-drop compensation Slow down power factor regulation Limit wind farm to 120 MW following a fast stop event

25 GE Study #2 Operating Process Changes Prior to control changes being implemented During local 115 kv switching: Maintain MW limits During local 115 kv outages: 80 MW limits During adjacent 230 kv and 115 kv system outages: MW limits

26 GE Study #2 Operating Process Changes After control changes implemented During local 115 kv switching: Maintain MW limits During local 115 kv outages: 120 MW limits During adjacent 230 kv and 115 kv system outages: no limits Indication of a fast stop event sent to the MPC control room Following a fast stop event, the MPC operator must assess the state of the grid and release the wind farm to full output if allowable

27 Control/Process Change Example A. Fault on L3 opens line B. Fast Stop trips up to 53 turbines prior to distance relaying seeing a fault C. After 2 minutes tripped turbines reconnect to grid with plant limiting output to 120 MW D. Operator closes L3 and releases farm to full output

28 Testing Test #1 Wind farm at 110 MW Opened L2 51 turbines operated on fast stop L2 was closed after approximately 2 minutes

29 Testing Test #1 Opening L2 w/ Fast Stop vs. Opening L3 w/o Fast Stop

30 Testing Test #2 Wind farm at 185 MW Opened L1 No turbines operated on fast stop Oscillations due to system response

31 Testing Test #3 Wind farm at 60 MW Opened L2 No turbines operated on fast stop

32 Performance Experience Overtripping occassionally occurs Remote 230 kv bus fault example

33 Will Lovelace Questions?