1. © Electric Power Group. 2014. All rights reserved. W IND F ARM O SCILLATION D ETECTION AND M ITIGATION WECC Joint Synchronized Information Subcommittee Meeting Salt Lake City, UT Sept. 9-11, 2014 Kevin Chen

2. © Electric Power Group. 2014. All rights reserved. What is the Presentation About? Page 1 UNDAMPED OSCILLATIONS DISCOVERED AT A WIND FARM April 2014

3. © Electric Power Group. 2014. All rights reserved. What Happened? Page 2  Oscillations observed by PMU located at a wind farm  Nature of oscillations – Low damping (less than 1%) – Present for 17 hours over two days  Magnitude of oscillations – About 1% in voltage April 2014

4. © Electric Power Group. 2014. All rights reserved. Oscillations First Noticed at 08:30 AM on Day-2 (1 min timeline) Page 3 Frequency April 2014 Oscillations observed by operation engineer for first time on RTDMS® at 08:30 AM on day-2 No oscillations in other frequency signals Oscillations only in wind farm PMU signal Built upon GRID-3P® platform. US Patent 7,233,843, US Patent 8,060,259, and US Patent 8,401,710. ©2014 Electric Power Group. All rights reserved.

5. © Electric Power Group. 2014. All rights reserved. RTDMS Replay Showed Start of Oscillations at 06:14 PM on Day-1 (1 min timeline) Frequency Oscillations not detected in SCADA Start time determined by playing-back RTDMS Oscillations determined to have started previous evening at 06:14 PM Oscillations not detected in SCADA Start time determined by playing-back RTDMS Oscillations determined to have started previous evening at 06:14 PM Start of oscillations 06:14 PM Page 4 April 2014

6. © Electric Power Group. 2014. All rights reserved. How would the Event have been Observed in SCADA? Page 5 April 2014  Synchrophasors provide crucial advantages: – Observability of oscillations in real-time – Oscillation damping and frequency tracking in real-time PMU Data Comparison between voltage signal from the event as captured by SCADA vs. PMU data End of oscillations SCADA Data

7. © Electric Power Group. 2014. All rights reserved. Sustained Oscillations for 17 Hours Page 6 April 2014 Oscillations present continuously for 17 hours on day-1 and day-2 ………. 17 hours Start End

8. © Electric Power Group. 2014. All rights reserved. RTDMS Display Shows Constant Oscillation Frequency, Low Damping Oscillation Frequency Damping % 3.3 Hz Less than 1% Low damping oscillations with a modal frequency of 3.3 Hz noticed throughout the duration of oscillations Page 7 April 2014 Constant frequency indicates presence of a single mode of oscillation

9. © Electric Power Group. 2014. All rights reserved. Typical Oscillation Frequencies in Power Systems Page 8 April 2014 Oscillation FrequencyTypical Cause 0.01 - 0.15 HzSpeed Governor 0.15 - 1.00 HzInter-area 1.00 - 5.00 HzLocal Control 5.00 - 14.00 HzTorsional dynamics 3.3 Hz oscillations fall under “local control” mode Indicates local wind farm control problem Helped in identifying “root cause” 3.3 Hz oscillations fall under “local control” mode Indicates local wind farm control problem Helped in identifying “root cause”

10. © Electric Power Group. 2014. All rights reserved. Operator Actions Page 9 April 2014 ActionImpactConclusion Disabling wind farm Automatic Voltage Regulator (AVR) NoneNo problem with AVR Reduction of wind farm output from 56 MW to 45 MW Oscillations decrease, but do not damp out completely Partial impact Further reduction of wind farm output to 40 MW Oscillations damp out completely Oscillations stop Resetting the wind farm controllers Oscillations damp out completely Solves problem

11. © Electric Power Group. 2014. All rights reserved. Oscillations Ceased after Power Output was Reduced at 10:54 AM on Day-2 (1 min timeline) Page 10 April 2014 Frequency Oscillations damped out on reduction of wind farm output from 45 MW to 40 MW Reduction in power output at 10:54 AM

12. © Electric Power Group. 2014. All rights reserved. How was it Confirmed that Control Settings Caused the Oscillations? Page 11 April 2014  Operators contacted manufacturer to research the problem  Manufacturer acknowledged settings were changed on Day-1 – Intended to increase the performance of wind farm – Changes were made concurrent with start of oscillations  Manufacturer restored original settings on controllers  Power output of wind farm was increased to pre-event levels – No oscillations detected  The root cause of oscillations was identified and corrected

13. © Electric Power Group. 2014. All rights reserved. What Conditions Triggered the Oscillations? Power HighPower Low Original Control Settings No Changed Settings YesNo Page 12 April 2014 Oscillations resulted from combination of changed controller settings and high power output

14. © Electric Power Group. 2014. All rights reserved. Summary Page 13  PMU at wind farm detected oscillations  RTDMS enabled the engineers and operators to observe oscillations and diagnose: – Low damping nature of oscillations – Oscillation location  RTDMS synchrophasor displays – Helped the operators to observe oscillations – Provided feedback to operators on effectiveness of mitigation actions – Provided insight to operators into oscillations through replay feature April 2014

15. © Electric Power Group. 2014. All rights reserved. 201 S. Lake Ave., Suite 400 Pasadena, CA 91101 (626)685-2015 www.ElectricPowerGroup.com Page 14 April 2014 For questions, please contact us at: contact@ElectricPowerGroup.com Or if you prefer, call us directly: (626) 685-2015 Thank You