0.5Amps Earth Leakage current on 4.7MW motor
0.5Amps Earth Leakage current on 4.7MW motor
(OP)
We are commissioning a new 4.7MW (6.6kV) induction motor. When the motor was tested on no load it was found that there is a 0.5 Amps current as Io. All connections checked & meggered (>9 GOhm), but nothing was found. Still it is showing 0.5Amps Io. Can anyone please advise from where this leakage can be & how dangerous is it to couple the motor & run?
Thanks in-advance
Kabos
Thanks in-advance
Kabos





RE: 0.5Amps Earth Leakage current on 4.7MW motor
First of all where are u measuring this current? Is this reading taken from the relay. Hope connection must be residual for the earth fault element. In this condition there are chaces of some curent in earthfault element due to mismatch of the CTs. Tell about the problem in detail?
RE: 0.5Amps Earth Leakage current on 4.7MW motor
You might want to take a look at your protective relay settings to see how far you are from a trip.
If you want some extra peace of mind you can take a megger reading.
RE: 0.5Amps Earth Leakage current on 4.7MW motor
As for an additional megger reading, we did...& the value is good >9 Giga.
RE: 0.5Amps Earth Leakage current on 4.7MW motor
Ideally it only cares about the current that passes within the window. But I have heard they are actually sensitive to placement of cables within the window. Cable forced against edge may not read quite as high as cable in center.
Shield currents can be a consideration also.
If you were continously passing 0.5A, I am pretty sure there would be some residual effect which would show up on the megger. So I suspect the explanation will lie in careful review of the ct.
I'm sure there are others here that can provide better advice on this. Also the power engineering forum can provide some comments.
RE: 0.5Amps Earth Leakage current on 4.7MW motor
If the CT is on the incoming cables, proper handling of the cable shield wires is critical. Review the relay instructions for recommendations. In general, the CT must be placed over a region of the cable where the shield has been removed, or the shield must pass through the CT twice.
Also, since the output of the CT is fairly low, twisted shielded cable on the secondary is always a good idea.
Good luck.
RE: 0.5Amps Earth Leakage current on 4.7MW motor
To add to other wise advice—realize also the significant difference between digital-display resolution and analog accuracy. In this case, a major portion of the reading may be ‘way-in-the-mud’; id est, noise.