Copyright © Snowy Hydro Limited and SEL 2017

Advanced Generator Protection and Monitoring Using

Transducer Measurements

Terry Foxcroft, Snowy Hydro Limited, Australia

and

Normann Fischer, Dale Finney, Satish Samineni, and Yu XiaSchweitzer Engineering Laboratories, Inc., USA

• Brief review of filtering• Applications• Conclusions

Overview

Protection Enhancements

Measurements Applications

Rotor and Exciter

Stator Winding

Generator Controls

LCI Starting

Bearings

Subsynchronous Resonance

Field Current and Voltage

DC Ground Current

Shaft Current

Shaft Angle

Typical Relay Data Acquisition System

VAC/IAC

VDC/IDC Antialiasing Filtering

Protection

Antialiasing FilteringADC

ADC

• Frequency-specific• Reject dc and the

harmonics• Suppresses inter

harmonics

Full-Cycle Cosine Filter

0 50 100 150 200 250 3000

0.2

0.4

0.6

0.8

1

Frequency (Hz)G

ain

(dB

)

• Includes all frequencies• Ideal for thermal

protection elements

RMS Filter Under- and Overestimates Magnitude

0 20 40 60 80 100 1200

0.5

1.0

Frequency (Hz)

Gai

n (d

B)

1.5

• Field quantity measurements• DC ground fault protection• Stator-field differential protection• Generator control monitoring • Subsynchronous resonance• Generator shaft currents

Applications

Generator Shaft CurrentsOil Film

Bearing HousingBearing

Rotor

Guide Bearing

Turbine Spiral Case

• Shaft current causes arcing

• Arcing removes metal from bearing face

• Guide bearing was also damaged

Damage to Thrust Bearing

Closer Look at Damage to White Metal Thrust Bearing

Preventing Shaft Current From Flowing

• Monitoring shaft voltage is not effective

• Monitoring shaft current is best

• Requires shaft CTs

Detection of Shaft Currents

Initial Rotor Position

Position After One-Pole Pitch Rotation

# of segmentsk# of pole pairs

=

100Pe

rcen

tage

50

0

75

25

3.11Frequency (Hz)

15.53 40.37 65.2227.95 52.80

No Shaft Current Frequency Spectrum

Shaft Current Frequency Spectrum(2 A Primary)

100Pe

rcen

tage

50

0

75

25

50.0Frequency (Hz)

250.0 450.0 650.0 850.0 1050.0

• Flexible and easy to install• Need to select integrator

range correctly

Rogowski Coil

• Additional generator measurements such as field voltage and current complement traditional protection

• Additional generator measurements increase the level of observability of the generator

• This allows generators to be operated more efficiently and economically

Conclusions

Questions