1. Wind Farm Oscillation Detection and Mitigation
WECC Joint Synchronized Information Subcommittee Meeting
Salt Lake City, UT
Sept. 9-11, 2014
Kevin Chen

2. What is the Presentation About?
UNDAMPED OSCILLATIONS DISCOVERED AT A WIND FARM
April 2014

3. What Happened? 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. Oscillations First Noticed at 08:30 AM on Day-2 (1 min timeline)
Frequency
Oscillations only in wind farm PMU signal
No oscillations in other frequency signals
Oscillations observed by operation engineer for first time on RTDMS® at 08:30 AM on day-2
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.
April 2014

5. RTDMS Replay Showed Start of Oscillations at 06:14 PM on Day-1 (1 min timeline)
Frequency
Start of oscillations
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
April 2014

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

7. Sustained Oscillations for 17 Hours
Oscillations present continuously for 17 hours on day-1 and day-2
Start
End
……….
17 hours
April 2014

8. RTDMS Display Shows Constant Oscillation Frequency, Low Damping
3.3 Hz
Constant frequency indicates presence of a single mode of oscillation
Damping %
Less than 1%
Low damping oscillations with a modal frequency of 3.3 Hz noticed throughout the duration of oscillations
April 2014

9. Typical Oscillation Frequencies in Power Systems
Oscillation Frequency
Typical Cause Hz
Speed Governor Hz
Inter-area Hz
Local Control Hz
Torsional dynamics
3.3 Hz oscillations fall under “local control” mode
Indicates local wind farm control problem
Helped in identifying “root cause”
April 2014

10. Operator Actions Action Impact Conclusion
Disabling wind farm Automatic Voltage Regulator (AVR)
None
No 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
Solves problem
April 2014

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

12. How was it Confirmed that Control Settings Caused the Oscillations?
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
April 2014

13. What Conditions Triggered the Oscillations?
Power High
Power Low
Original Control Settings No
Changed Settings
Yes
Oscillations resulted from combination of changed controller settings and high power output
April 2014

14. Summary 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. Thank You For questions, please contact us at:
Or if you prefer, call us directly:
(626)
201 S. Lake Ave., Suite 400
Pasadena, CA 91101
(626)