Generator Coil Clearance 1

[QCE]

Is there a general rule for the clearance between coils in a LV machine? Would the clearance be drastically different between a 8kV machine and a 15kV machine. Are touching coils acceptable? If the clearance is small should the gap be filled to stop corona?

 

[electricpete]

On your last question, it is my understanding that it is better to fill the gap than to have a small airgap.

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[jbartos]

Suggestion: The generator winding design is dependent on the machine Power Rating beside voltage rating. The major concern is about the winding structural soundness to avoid the winding vibrations, noised, insulation damages, etc. Low voltage low power rated machines often have the winding tied together outside the stator slots to improve their physical solidity that minimizes vibrations, etc.

 

[edison123]

Depening machine diameter, normally coil to coil clearances in end winding zone is normally between 3 mm to 6 mm, which is more than to enough to stop corona in that zone. As jb says, the end winding is all braced strongly to prevent vibration and also withstand short cirucit forces.

 

[QCE]

Thank you guys,

I am talking about a 30MW hydro generator so the diameter is large and the MW is relatively low. I'm mostly concerned about coils that are touching. Do you think it is acceptable to have line end or any coils touching.

QCE

 

[edison123]

For such a big diameter m/c, I would expect 4 to 6 mm coil to coil clearance. If all the coils have no clearance, then end winding insulation thickness is excessive (normally it is about 75 to 85 % of slot wall thickness). If only some coils are touching each other, then it is due to poor forming of coils and poor workmanship during erection. As noted before, the end winding should be sufficiently braced to withstand short circuit forces. If the coils have no clearance, then they could not be tied down adequately.

Is this an original winding or a rewind job ?

 

[QCE]

It is a rewind and only some of the coils are touching. The end turns are braced together for mechanical strength in the front of the coil. The coils that are touching are touching on the top (knuckle) of the coil were the rear leads exit the coil. What should the response to the rewind contract be that is doing the installation? They of course say that touching coils is fine.

 

[edison123]

QCE,

Can you post some pictures of your winding here ? Other day I saw in some post, pictures being uploaded in this forum. I haven't a clue how they were done.

If the series joints or take of leads are touching, then a good winder can form them properly to create some space. He can insert some insulation blocks and tie them to the joints to keep them separated.

 

[QCE]

Actually I have seen it before were the winding contractor has seperated and placed insulation between them. However this winding contractor has got the approval of his engineeering department to leave the coils touching. I am a little concerned about stress on the coils during expansion or rubbing during vibration. Should I be concerned? It is actually the end turns of the coil that are touching not the series connections.

 

[edison123]

Could you mail some pictures of the winding to eewemf@hotmail.com ?