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Transcript of Copyright © SEL 2012 A Comparison of Different Signal Selection Options and Signal Processing...
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
Outline
• Existing Subsynchronous Resonance (SSR) detection methods
• Signal input options
• Signal processing tools
• Application results
• Conclusions
Background
• Series compensated lines
• Types of SSR
1. Induction Generator Effect
2. Subsynchronous Torsional Interaction
3. Subsynchronous Control Interaction
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)
Existing SSR detection methods
• Tex Relay
• Torsional motion relay
• Armature current relay
Microprocessor based methods
• Patent by Southern California Edison
• Patent by ABB
• ERLphase method
Input signal options
• Negative sequence current
• Voltage across the series capacitors
• Generator terminal currents and voltages
• Generator speed
DFT result for voltage and current of the capacitor bank
0 20 40 60 80 100 1200
5
10
15
20
X: 35.4Y: 19.27
Frequency, Hz
Vol
tage
, kV
DFT result of voltage and current of the capacitor bank
X: 60Y: 17.9
0 20 40 60 80 100 1200
0.05
0.1
0.15
0.2
X: 60Y: 0.1624
Frequency, Hz
Cur
rent
, kA
X: 35.4Y: 0.1029
Signal processing techniques
• Fourier Transform
• Short time Fourier transform
• Wavelet transform
Heisenberg boxes (STFT)
Heisenberg boxes (WT)
DFT, STFT and WT
Real world event
0 0.2 0.4 0.6 0.8 1-1000
-800
-600
-400
-200
0
200
400
600
800
1000
Time, sec
Cur
rent
, A
Generator current waveform for a real world SSR case
Application results (FT)
0 20 40 60 80 100 1200
50
100
150
200
250
300
350
400
X: 25Y: 380.9
Frequency, Hz
Mag
nitu
de,
ADFT result of IA
X: 60Y: 176.3
X: 95Y: 32.94
Application results (STFT)
Application results (WT)
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.
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.
Questions?