Commutator risers on 4000HP motor

[AutoXer]

We are having a spare armature built for a 4000HP motor.

In the past, we've experienced problems with the commutator risers breaking at their welded joints. The risers are about 14" long.

We have retrofitted one of the existing motors with a riser support ring. The risers are tied to the support ring in two places, equally spaced. We've also added a kink in each of the risers to allow some flex. We haven't had any problems since the retrofit.

The new armature will feature a support ring, but the maufacture isn't so sure that we need the kink in the risers. We think we want the kinked risers, but we aren't sure. The risers will likely cost us a little extra and will add lead time to the armature delivery.

Does anyone have any experiance with this subject? Any input would be appreciated.

 

[ScottyUK]

Not a direct answer, but on much larger machines in the generation industry we use laminated flexible links at major mechanical stress points to decouple bars from each other and from bushings. I can't exactly picture your arrangement - are you able to post an image of one of the affected machines? There is an option to upload files with your reply.


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If we learn from our mistakes I'm getting a great education!

 

[AutoXer]

Here's a shot of the retrofitted design showing the kink. I'm fairly sure that this is just a bend in the solid copper riser and not a laminated section.

 

[edison123]

You have tied the risers in two places to make a rigid structure and then created a kink to create flexibility. Kinda contradictory, ain't it ?

In my repair shop, we have rebuilt such commutators with long risers with additional braces but with no kink. These 2000 HP motors have been working fine for over 5 years now.

Do you want the kink for any specific reason ?

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[Compositepro]

After looking at the picture my opinion is that the kink is a really good idea. You have relatively delicate risers attached to a massive structure that is made of a mix of different materials and that is going to see large temperature swings. Without the kinks small dimensional changes could put large stresses on the risers. The kinks make the risers flexible.

 

[ankervik]

I agree with Compositepro. Long 14" risers should have a kink or "swans neck" in them to reduce the effect of thermal and centrifugal stresses. It could result in a very expensive repair at a later date without. Most of the large armatures I have seen with long flexible risers had some kind of stretch profile in them.

 

[roydm]

Woa,
Thats a pretty serious looking comutator, mind me asking what you use a 4000 HP DC motor for.
Regards

Roy

 

[AutoXer]

This is one of two motors powering the work rolls of a 110" reversing roughing mill. The mill is used to process ingots of nickel based alloys into plates, blooms and slabs.