Answer / tendulkar

adding information to this question....
transformer is used for three purposes
1.to step and atep down the volatge.
2.for impedance matching
3.for isolation.
transformer used for isolating purpose is called isolation
transformer,it is used when there is a requirement to break
a continues big circuit,it should be noted that the voltage
at primary and secondary ends of this transformer is same

Answer / bhadrappa

for impedance matching and isolation.

it is used when there is a requirement to isolate the power ckt with control circuit and to transfer the pulse.
example: thyristor working in 415 volts firing circuit under 5volts.

Answer / nagesh.patwari

Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass. Transformers that have a ratio of 1 to 1 between the primary and secondary windings are often used to protect secondary circuits and individuals from electrical shocks between energized conductors and earth ground. Suitably designed isolation transformers block interference caused by ground loops.

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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