13.2kv motor coil inspection û missing carbon
13.2kv motor coil inspection û missing carbon
(OP)
Attached is boroscopic picture taken looking into the vent duct area of a 13.2kv motor during teardown inspection following 20 years of service. The motor passed a dc step voltage test to 32kvdc with no non-linearity.
The motor has Thermalastic insulation (wound by Westinghouse in 1980's).
The corona suppression system in the slot is provided by tape (polyester glass tape impregnated with carbon).
A red surface coating is applied over all.
The photo shows apparent white residue from partial discharge.
The red outer coating is missing.
What is visible appears to be glass type tape, but there is no hint of carbon black material.
That is the real puzzle... how can there be no carbon showing in this photo?
The motor has Thermalastic insulation (wound by Westinghouse in 1980's).
The corona suppression system in the slot is provided by tape (polyester glass tape impregnated with carbon).
A red surface coating is applied over all.
The photo shows apparent white residue from partial discharge.
The red outer coating is missing.
What is visible appears to be glass type tape, but there is no hint of carbon black material.
That is the real puzzle... how can there be no carbon showing in this photo?
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(2B)+(2B)' ?





RE: 13.2kv motor coil inspection û missing carbon
RE: 13.2kv motor coil inspection û missing carbon
We decided to rewind this motor, even before it got to the shop based on a variety of factors unrelated to the as-found condition of this particular motor (criticality of the application, performance of similar vintage/style motors, very long time until next availability). I am still very interested to understand what the heck is going on with this indication.
Another observation from the same motor was: looking at where the coils come out of the core, you can see white powder at the interface between the coil and the core. It seems the semicon is not present or not effective at that location also. I'll try to get a photo.
The possibilities would seem to be:
A – no semicon (carbon) was ever applied
B – there is a semi-con layer under the armour
C – the semicon came off somehow, possibly because it was not correctly applied to begin with.
They all seem far out to me. C seems least far out among them.
What do you guys think?
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(2B)+(2B)' ?
RE: 13.2kv motor coil inspection û missing carbon
Did your shop do a Doble test?
RE: 13.2kv motor coil inspection û missing carbon
Due to hassles with the paints, I have switched over to tape based systems for both slot and end winding more than 10 years back. Not a single issue so far. The additional cost of tape based system is worth the money.
Muthu
www.edison.co.in