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

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

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

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

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

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

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

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

Typical Oscillation Frequencies in Power Systems Oscillation Frequency Typical Cause 0.01 - 0.15 Hz Speed Governor 0.15 - 1.00 Hz Inter-area 1.00 - 5.00 Hz Local Control 5.00 - 14.00 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

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

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

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

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

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

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