1. Copyright © SEL 2012 A Comparison of Different Signal Selection Options and Signal Processing Techniques for Subsynchronous Resonance Detection Yu Xia, PhD, Member, IEEE Normann Fischer, Senior Member, IEEE Schweitzer Engineering Laboratories

2. Outline Existing Subsynchronous Resonance (SSR) detection methods Signal input options Signal processing tools Application results Conclusions

3. Background Series compensated lines Types of SSR 1. Induction Generator Effect 2. Subsynchronous Torsional Interaction 3. Subsynchronous Control Interaction

4. Challenges Low magnitude of oscillation Low frequency range Tight response time requirement (Speed) High amplitude of fault current Avoid false trips (Security) Recognize SSR (Dependability)

5. Existing SSR detection methods Tex Relay Torsional motion relay Armature current relay

6. Microprocessor based methods Patent by Southern California Edison Patent by ABB ERLphase method

7. Input signal options Negative sequence current Voltage across the series capacitors Generator terminal currents and voltages Generator speed

8. DFT result for voltage and current of the capacitor bank

9. Signal processing techniques Fourier Transform Short time Fourier transform Wavelet transform

10. Heisenberg boxes (STFT)

11. Heisenberg boxes (WT)

12. DFT, STFT and WT

13. Real world event Generator current waveform for a real world SSR case

14. Application results (FT)

15. Application results (STFT)

16. Application results (WT)

17. Conclusions (1) Existing SSR detection methods were reviewed. Different signal selection options and signal processing techniques were compared. Existing methods either do exclusively time domain analysis or exclusively frequency domain analysis.

18. Conclusions (2) STFT and WT decompose the signals in both time and frequency domain. WT overcomes the drawbacks of FT and show a clear relationship between the magnitudes of different frequency components and time.

19. Questions?