TK V500 semi-hermetic compressor insulation test varied results

[swampy84]

Hi all. Went to a job other day and customer was complaining
About no standby operation. (240v single phase) Checked the source and found mains power
Had been tripped. Meggered the extension lead, tested all ok.
Reset the mains, unit started but cut out very quickly.
Reset mains once again, this time manually pushing the contactor in
with the same result once again cutting out immediately.

Isolated all wiring from windings and found windings going straight to
Ground @ 500V test.

Strangest thing though, I have since removed the compressor and drained the oil
Only to retest the windings on a bench and @ 500 V resistance is infinite!
Has anyone else seen anything like this before?!

[cadwaladr]

Put the oil back in,then test again

[swampy84]

Really? What if it tests ok then?!!?

[Grizzly]

Really? What if it tests ok then?!!?

Damp motor winding which may of dried out since the first test, COULD? be the cause?
Moisture in a stored motor will give similar results.
Strange given what you have done all the same!
Swampy has a good point if using synthetic oil within this comp.
The oil has the ability to become highly saturated with water if not stored or used correctly.
Grizzly

[swampy84]

Good point, never really thought of that really. In which case if the windings have gone to ground due to poor oil condition... The oil used is polyol ester oil. So yeah very hygroscopic.....

[swampy84]

I guess that long story short is I don't want to put this motor back in
That may only last a few months as it's in a prick of a spot.
Mind you I don't want to replace if It's not necessary either.
Surely if the oil has gathered so much moisture and or has turned acidic
The windings wouldn't be in the best condition

[cadwaladr]

If in doubt sling it out!

[cadwaladr]

I used to get problems with early ones the terminal box on the compressor was prone to letting water in ,I used to put a small sheet of ally on the grill/cover it was worse if it snowed.