I have a 120 HP 460 VAC Inverter duty motor driven by a VFD, yesterday the drive tripped on output overload. While checking resistance between the load size terminals to the motor (which were isolated from the drive and only connected to the motor) I measured a very low resistance of .1 ohm between windings. I then checked the leads to ground and found that the circuit is grounded, which I still need to troubleshoot. I thought the reading between windings was low so I checked another similar drive and motor and found the resistance between windings low as well. So what would be a normal reading between windings? I thought a reading of a few ohms was the norm.
I guess my question to you would be what resistance did you anticipate?
This is a very simple explaination.
When you measure winding resistance you are measuring a simple length of wire of that winding. Would not one expect that the resistance be very low then since you are measing resistance with a DC source? If you measure the resistance of each individual winding one would anticipate that each one would result in a very similar resistance reading since all windings would be made up of the same length and gauge of wire. As such measuring winding resistance of each winding in and of by itself really is of not relevance unless you compare the reading of each winding and find that there is a relevant difference which may indicate some of the windings may have shorted to themselves resulting in a lower resistance or open which would be strange should the motor still be operational.
When AC voltage is applied to the motor it is the interaction between the stator and the rotating rotor that provides the needed stator resistance which is not evedent when measurng the simple winding resistance with a ohm meter when the motor is de-energized.
Then there is an insulation test that would also assure that the winding to ground resistance is within acceptable values and that there isn't insulaion failure in progress.
Personally, I would target an insuation test by having the motor meggered to varify the insultion integrety. You may not find a thing an would have to consider another issue.