Answer / rk

The insulating power factor test, better known as the ”Doble
Test”, is a complete overall test of the insulating
properties of a transformer. Elements such as carbonization,
ionization, moisture, and heat can breakdown the
insulation's strength. The Doble test measures the power
losses due to leakage current through the insulation.

One of our gas turbine generator unit "1st stage rotor ground fault" alarm was occured several times. we tried to measure some voltage vulue ground fault protection relay (UNS3020a made by ABB and we measured the value of: Ground: 0.9VDC 5V: 5.8VDC 24V: 23VDC u+: 300 – 350mVAC Rf1: 17.5mVAC Rf2: 17.6mVAC The unit still running and the alarm was reset. As of 6pm yesterday and unitl now no alarm happened again. I our protection relay was defective?

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