Insulation problems

[guntherb]

I have the following problem

a gearless mill drive motor

We have numerous problems with insulation. ie partial discharge.
The main problem I think is the derating factor at high altitudes.(insulation at high and cold altitudes over 2000 metres)
Could I please have suggestions around this

 

[edison123]

Motors have to be derated at altitudes over 1000 meters. You need to talk to the manufacturer about the amount of derating.

What tests have you done to confirm partial discharges ? Usually, it is due to low quality coils.

 

[TheBlacksmith]

I suspect you have a VFD to control speed since you say it is gearless. The rapid voltage rise and switching can exacerbate partial discharge tendencies. IRIS power engineering has some papers on this; look them up on the web.

 

[itsmoked]

An output choke could also help as it will round off those sharp insulation thrashing VFD waveforms.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

Dertating for high altitude is due to low air density which reduces cooling capacity. It is a reduction in loading, not voltage. As such, it will not change the motor tendency for partial discharge which depends on voltage stresses.

I am with edison in wondering how you conclude you have a partial discharge problem? Testing? If so please share your results. And has it changed or always been there? Inspections? If so, what is the location of the partial discharge (slot exit, end turn inter-phase, etc) ? What is the voltage and horsepower of the machine? And what type insulation system (vpi or B-stage). And how old is the insulation system ?

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