wedges out of rotor

[gaux]

We have rewind a dc motor 400 KW and 1000 rpm, and after rewind the rotor we mount it on the application, after one week we find some wedges out.from the rotor... the insulation was ok, cause we have this problem in two times.... we use fiber wedges,.. could you recommend some kind of wedges or some tip...... or link.... maybe is a question of the vernis....??

 

[ankervik]

Slot wedge material should have at least the same thermal classification as the rest of the insulation system so that its mechanical strength is not degraded by operating temperature. Vulcanized fibre has a maximum service temperature of 120°C, and although it is pretty strong & tear resistant it is also very flexible & more susceptible to moisture. You would probably get away with it in a stator slot but it isn’t really suited for rotors or armatures. I would suggest using a glass/polyester pre-formed wedge, or a glass/epoxy G-11 laminate.

 

[electricpete]

I don't know the answer but sounds like good advice above.

What's a "vernis"

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[ankervik]

Sorry...I forgot to ask. What type of varnish system are you using?

 

[oftenlost]

I agree that the wedge material needs to be changed. I have had good results with G11 wedges. One caution with G11 though. This material is composed of layered glass sheets impregnated with epoxy. In milling the wedge angle to fit the slot I have found that matching the wedge groove angle is critical to prevent the wedge from delaminating.

 

[gaux]

sorry for the delay in reply but i was with others problems..... i think, i´´m not a expert, they dip the rotor in varnish, polyester varnish.....in your opinion, what king of varnish is better for a rotor ?
Could you send me a link to some info about the g11 wedges....?
thanks a lot

 

[ankervik]

Gaux,
I guess your location is France...yes? The attachment ought to help you out with info on G-11 laminates (BTW, I think "Vonn Roll" still have an office in Delle).
Polyester based varnish is fine for most dip & stove applications (stators), in the absence of a VPI system maybe you could double-dip larger rotors/armatures.

 

[ankervik]

Sorry the link got mixed up. Here is the product sheet for class "H" G-11 laminate (also available is class "F).

 

[gaux]

sorry ankervik, i heard some times that, when you varnish by dip a rotor or a armature is no a good pratice to redip again it, cause the varnish didn´´t enter more in the holes, what do you think? is it a good pratice?
thanks

 

[ankervik]

Gaux,
As I said VPI is the best method but if you don't have VPI then dip varnish is your only alternative.
You are quite right that if an armature (or stator for that matter) has been dip varnished well enough, then a second dip is unlikely to achive any penetration. It will however contribute to the overall mechanical strength of the winding.
Warming the armature slightly before dip varnishing will increase penetration, but on the other hand it can degrade varnish quality and affect the hardening process. Its kind of a playoff. Maybe it would be an idea to speak to your supplier & ask if your present varnish is suitable for your needs?

 

[gaux]

i see you know more than me about varnish.... i read something that make me think... how much a varnish could be affected into their mechanical strengh cause of warming it.....
thanks a lot....

 

[ankervik]

Impossible to say, there are so many different types of polyester based varnish. You would have to check with your supplier or consult the product data sheet. Many polyester varnishes use Xylol (Xylene) as a thinning agent & it has a low flash-point.