Megging 3 phase 480v 9 wire motor

[devonhilburn21]

I need help. I have a dura pulse gs3 VFD on a 3 phase 480v 3 phase 9 wire motor. VFD trips on ground fault every now and then. It may trio every other time the motor kicks on or every tenth time, it just varies. I’ve isolated my line and load cables to the motor and ran insulation test, all good. Now to the motor. Disconnected all 3 line wires, ran test and got .1 megohm on each phase to ground. Then isolated every wire (disconnected 4-7, 5-8, 6-9 and of course line wires). I get 550 megohms on each phase to ground. Is this motor bad? Is the VFD bugging out? Any help is appreciated.

 

[waross]

It doesn't sound good.
You can provide us with more information if you connect 4 to 5 to 6 and megger 1, 2, or 3 to ground.
I expect to see about 183 megohms to ground.
Also, megger 7 or 8 or 9 to ground.
The motor should have 6 equal windings.
You are reading 550 Ohms to ground on one winding. I assume line 1 to ground with wire 4 left open.
For 6 windings you should read 550 meghoms for each winding.
A megger test on any line with the 4-7, 5-8, and 6-9 jumpers in place should read 550/6 megohms. That's about 92 megohms.
You are reading 0.1 megohms.
It looks as if one or more of the windings in the 7,8,9 group is failing to ground.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!