Motor DIP and Bake versus VPI

[davva]

we have old motor going for overhaul and OEM recommended procedure written at time of manufacturer (1978) was to DIP and bake.

Would you recommend now to VPI?

Also regarding test (it is 440V 300kW motor), is a surge test applicable for this random wound machine?

 

[mikekilroy]

just my opinion but if this motor is not used on a vfd drive, then it seems like dip/bake should be fine - it did last 30+ years......

If used on vfd I would do no less than vpi as the high voltage spikes will ionize any air (breaks down varnish) in winding varnish gaps and potentially significantly shorten the motor life (down from last 30+ yrs to I have seen as little as 3 minutes)

 

[electricpete]

Consider doing neither (unless the motor is being rewound, in which case vpi).

For one thing, most shops will not put a non-rewound stator into their vpi tank for fear of contamination (even after steam cleaned/bake).

For either dip/bake or VPI performed after initial rewind, you have to consider possible negative effects on thermal performance (adding layers of thermal insulation, and clogging cooling passages).

Perhaps substitute a robust electrical test (after clean/bake/inspect). If passes, you have pretty good confidence in existing winding. If fails, it'll push you to rewind but you'll be glad you identified it through testing at a time you could do something about it.


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(2B)+(2B)' ?

 

[electricpete]

Also regarding test (it is 440V 300kW motor), is a surge test applicable for this random wound machine?

Yes. Random and form wound are both included in IEEE522 and it is certainly a useful test for both. Do recognize that it is potentially destructive. Meaning that if it fails, you may be forced to rewind. But if you have selected your test voltages correctly and still fail, one could argue the winding was in bad shape and it's a good thing you found it at this time.


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(2B)+(2B)' ?

 

[davva]

Thanks all.

Electricpete. Yes, I had read that IEEE522 was o.k. for random and form motors (LV included) despite the title of the standard suggesting it is just for form wound motors. The more I looked into it, it seemed to suggest that it was only a suitable test for high voltage motors that may see switching transients. The reference I had seemed to suggest it would be a good Go / No-go test for LV random wound motors as well.