Is there a IEEE standard for scheduling motor bake and dip frequency?

[Electic]

I am doing work for a facility that has a robust PM program based on plant experience. They wish to convert experience into written procedures. I am seeking published industry standards or article to support (or correct) their procedures.

We have been tracking down recognized standards that support their practice, but have not found one for recommending motor bake and dip frequency or criteria for when this should be accomplished. Is there an article or standard that offers guidelines?

[The facility has a good track record of scheduling motor PM including vibration monitoring, bearing temp, winding, on-line electrical tests and bake and dip PM. I do power distribution work and am not familiar with the details of the motor programs.]

 

[starkopete]

You may want to look at IEEE Std. 432-1992, Guide for Insulation Maintenance for Rotating Electric Machinery (5 hp to less than 10,000 hp).

 

[electricpete]

We don't ever dip and bake. The downside of dip and bake is you accumulate thermal insulation and also possibly increase blockage in cooling ports. The upside? Not much I can see if you already have a vpi winding. It might be a good idea once if you have a winding which is mechanically loose. Maybe someone else can explain any other reasons why anyone would ever want to dip and bake.

I am pretty sure there is no IEEE standard which recommends PERIODIC dip and bake.

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[Electic]

Thanks for the answers gents.

I might have misunderstood whether they are performing dip and bake on schedule. I thought they were cleaning the windings (steam?) then baking to drive out impurities and then dip to restore any lost insulation. That is a guess. My questions was whether there is an industry standard based on service/severity and you have answered my question.

 

[electricpete]

Steam clean and bake is a standard part of motor refurbishment. The "dip" part is the controversial part that I disagree with.

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[starkopete]

Electripete is correct that there is probably no standard that recommends periodic "dip" and bake. The Std. that I suggested deals with evaluating and cleaning the insulation, it stops short of suggesting any "repair" to the winding. I also agree with him that it is highly questionable if there is any upside to "dipping". If the insulation is that bad, rewind it or replace the motor. "Dipping" a thermally aged or otherwise compromised winding might buy you a little time but it just as easily may cause the motor to fail sooner due to loss of thermal conductivity as he suggests.
I have dealt with some specifications where a "dip" is required every time the motor is repaired. I realize that that is an extreme and you are not advocating it. But I have always felt that "dipping" is of questionable value and advise that it not be part of a specification. Do we "dip"? Sometimes, ultimately the customer is right, they pay the bill (but we won't warranty it). Do we recommend it? No.

 

[edison123]

I agree with both petes.

As a rewinder, I never dip or revarnish windings during repairs and overhaul. The machine is dipped and baked only when it is freshly wound. Subsequent dips will only degrade the residual life of the windings due to heat trapping by additional thermal layer of varnish. Also, any inaccessible accumulated winding dust will be permanently trapped by the varnish dip.