shorting out sliprings 1

[kenneth7]

I have a 3.3kV 400kW slip ring motor. Does any know of a system where the slip rings can be shorted at the motor once it has started and possibly the brushes lifted off the slip rings

 

[Marke]

It is normal to short out the rotor once the motor is up to full speed, but this is done at the ouput of the brush gear.
I have seen motors used with the rings permanently shorted and the brush gear removed, but these are driven by a VSD. If you use any form of primary starter, you must have resisance in the rotor circuit during start or no torque will be developed.
Regards, Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion: Normally, the slip rings have brushes on. This obviously wears brushes. The slip rings are needed during the normal wound rotor motor operation since they shorten the rotor winding. Then, large currents flow though slip-rings and brushes. To modify this concept, some customization would have to be implemented. Perhaps, rotating solid state electronic switches could implement short circuits among slip rings and some mechanism added to lift the brushes, once there would not be current flowing through shortened starting resistors of the wound rotor motor. This may sound terribly complicated but it seems to be feasible to implement from the engineering/design standpoint.

 

[Marke]

Nice idea in theory, but the problem is that the rotor currents are quite high and so the physical size of the SCRs (6 required) and the heatsinks just would not fit into the enclosure. This would need a specially designed machine, at which time you could put the rotor resistors on the rotor also with cetrigugal swiching to sw=ich them out. Not really a retrofit option!!

Best regards, Mark Empson

http://www.lmphotonics.com

 

[Cubrilo]

Of course. There is an old system (at least 80 years) where lever pulls up brush holders and simultaneously push copper cylinder on slip rings.Construction is only mechanical and we can say trivial.

 

[jbartos]

Thanks to the previous posting for a nice piece of history.

 

[kenneth7]

The answer given by Cubrillo is the one I was looking for but surely there is a modern automatic system that does the same job

 

[jbartos]

Suggestion: As far as any worries about the rotating semiconductors are concerned, one may recall large generator exciters that have their rectifiers rotated and adequately cooled.

 

[Marke]

jbartos
Agreed, but if you are trying to mod an existing machine, then it gets difficult due to the confined space.
Mark Empson

http://www.lmphotonics.com