(No) Impregnation for motor stators 3

[cgmorganti]

Have anyone tested the life of a motor without impregnation of the stator?
Do anyone know motors produced by someone without impregnation of the stator?

 

[jclough]

Foreign made steppers and universal motors are usually not impregnated.

 

[aolalde]

Impregnation of motor and generator windings is done mainly to provide mechanical support to the winding.

As the machine size increases, the electric attraction and repulsion between conductors increases with the current driven.

If the conductors are allowed to vibrate, eventually abrade the insulation leading to a failure.

The life of a winding without impregnation will depend on the machine size and how tight fits the winding into the slots, probably toy motors are made that way.

Large motors with medium voltages will last a few hours if not minutes.

 

[electricpete]

I'm not sure I can give an answer, but for anyone to address your question you will have to be more specific about what you are asking.

What size motors.

What do you mean by no impregnation? No global vacuum impregnation? What about a B-stage coil... do you consider that impregnated? Large motors can be made with B-stage coils (no VPI) and operate reliably for decades.

VPI is the state of the art and preferred for high end applications imho.

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[jbartos]

Suggestion: Often, toy motors are seen without stator impregnations. Some toys do last years, when occasionally used.

 

[edison123]

Random wound and form wound lv (<600 V) are invariably impregnated to 1. fill the voids with resin/varnish for improving dielectric stength 2. to bind the mechanically to prevent winding / coil movement 3. to prevent moisture entry etc.

Form wound mv windings (3.3 KV and above) may be vacuum pressure impregnated with B stage coils or use resin rich non-impregnated coils, both systems having been time tested.

Advantage with resin-rich system (non-impregnated) windings is that it is easier and cheaper to rewind them.

pete,

I have not come across machines being operated with B stage coils, which are only semi-cured and are not fully fit for dielectric stresses until they are fully cured under VPI (global or coil wise)

 

[electricpete]

B-Stage was pioneered by GE. Still in wide use. I find it a very common choice in repair shops when the stator is too large for their vpi tank.

The curing occurs under high temperature when the stator is baked after winding.


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[jbartos]

Suggestion: Visit

http://www.electromash.com/eng/elremob/p6/elremob_p6.htm

http://www.nwibrt.org/Specifications/acmotor.doc

etc. for more info

 

[UKpete]

I think B-stage refers to tapes pre-impregnated with resin (though they feel quite dry to the touch), used on form-wound stators and are cured-off in the oven after winding.

 

[aolalde]

"B-stage" refers to tapes loaded with a semi cured resin, regularly stored at low temperatures to avoid reaching of the "C-stage"(fully polymerized stage). This type of tapes had limited shelf life.
This insulation is broadly used on form-wound Generator stators 7.5 to 15 kV. The coils are cured in a molded-press under temperature.
Isola and US-Samica are some of the leading tape manufacturers in USA

 

[jbartos]

Suggestion: The motor windings can be tested before impregnation. Visit

http://www.electromash.com/eng/elremob/p6/020105.htm

for the testing equipment.
If installed unimpregnated, then the slots have to be insulated.

http://www.cedrat.com/software/motor-cad/pdf/Motor-CAD_IEMDC_2001.pdf

for:
Additional methods used to increase the winding
dissipation include improved winding impregnation
techniques and potting of the end-windings. Vacuum
impregnation can eliminate air pockets within the winding.
For instance the winding shown in Figs 5 & 6 benefit from a
decrease in temperature rise of around 9% when the motors
are perfectly impregnated compared to a 50% impregnated
motor.