Measuring Ground Current

Your question is hard (for me) to understand.

Is that motor / drive actually tripping due to ground fault and you're trying to find out why, or are you trying to determine the correct setting for the ground fault relay to protect the motor / drive?

Thank you for your response regarding my question,actually the drive is tripping due to ground fault but we need to indicate the actual ground current that makes us to become alert before tripping.

See #2.

I'd probably like to have a strip chart recorder in the CT circuit to see what the current looks like before tripping.

But, you have a setting on the current ground fault trip device--obviously the ground fault current is exceeding that setting when it trips. I guess you want a warning before the trip--I'm not sure how much warning you can get, but try setting another ground fault relay, driving an alarm, at 1/2 the value of the trip...

Yes, it is very easy to measure. A current transformer of expected maximum earth fault current and an ampmeter will do the job. The earth fault current is the ratio of the applied voltage over the total earth fault loop impedance. I = V/ R, were R is the resistance of earth fault loop.