Rotor Earth Fault Relay


Thread Starter


Hello Every one,

I want to know about the working principle for the rotor earth fault relay? and is the working principle same for the earth fault relay in battery chargers? I learned there are different principles for rotor earth fault relay working.

the three prevalent types of protection used are:

1) DC-Voltage Measurement
A voltage-relay is connected between the center-tap of resistor in parallel with the rotor, and earth rotor winding and earth. Virtually any EF will produce a voltage which is detected by the relay, except a fault near the center of the winding. This covered by a second tap on the resistor some distance from center.

2) AC-Current Injection
An auxiliary ac source is connected between the rotor-winding end and an ac voltage-relay, thru a capacitor. This eliminates the situation above when the EF occurs near the center of the winding.

3) DC-Injection
A DC source is provided that sets up a voltage greater than that of the rotor. It will detect an EF anywhere along the rotor-winding. But, its magnitude also varies, i.e., unlimited at the winding end where it's connected, to a minimum value at the opposite end of the winding. Thus, a current limiting resistor is added.

Phil Corso
Hello sudamadhav,

Yes. Generally, the method of earth fault detection for a battery charger is very different from the method used for earth fault detection on a rotating generator field.

To be certain about how the equipment at your site works, you'll need to consult the manuals for the equipment at your site. I'm very certain you will find the battery charger earth fault detection method/scheme is relatively simple, and the generator rotor earth fault detection method/scheme is more complicated.

Please write back to let us know what you find!