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?