NEMA submergence test 2

[electricpete]

We are thinking about specifying NEMA submergence test following rewind for large critical motors in outdoor environments.

Does anyone have experience with this test? Is it useful? Can it cause latent damage that wil create problems later?

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[KB3HHC]

I don’t have any first hand experience with this, since it’s not our normal practice in this company. However, I had a conversation with a large motor supplier last year about it. This particular supplier said they have equipment to do a spray test, but not a submerged test. The spray test is an alternative per MG1. He said that about 20-30% of buyers specify the spray test (esp for API-based specs). They spray the stator first, then apply the hipot (i.e. not at the same time). He said the failure rate is approximately the same as for the normal hipot. In other words, the defects would have been found by the normal (dry) hipot anyway. The stators themselves are exactly the same whether the test is specified or not. There didn’t seem to be much value in specifying this test. Most large motor suppliers will confirm that their insulation is a ‘sealed’ system – i.e. capable of passing this test. I don’t believe there would be any harm in specifying it.

 

[bill1055]

A motor shop I worked at years ago had a customer that required this test. A good VPI winding had no problem passing the test, the only extras involved were a post test steam and bake to remove the water from the test. The water was treated with a wetting agent to reduce the surface tension. I don't believe the wetting agent, if allowed to remain on the winding, would do any harm, but better safe than sorry.