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Sparking brushes of Synchronous Motors

Sparking brushes of Synchronous Motors

Sparking brushes of Synchronous Motors

(OP)
I have two identical 4000hp Synchronous Motors operating reciprocating compressors. The '–ve' terminal brushes on one machine tend to develop spark. The excitation control system (GE-Stat-x-ator) has almost the same volts/amps/pf for each machine, as the loading is identical.  Need help to find root-cause for the carbon-brush spark?

RE: Sparking brushes of Synchronous Motors

First thoughts:
rough slip ring causes bouncing
not enough spring tension
brush face condition

Is it a condition that developed over time?

=====================================
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RE: Sparking brushes of Synchronous Motors

Lack of maintenance?  

RE: Sparking brushes of Synchronous Motors

(OP)
No mechanical/maintenance type issues. New brushes/slip-rings/holders installed 3-4 weeks back. Enclosed & instrument air for cooling. Each time set of brushes on '-ve' terminal develop spark.

RE: Sparking brushes of Synchronous Motors

Change the polarity periodically.  Then both sets of brushes will wear more evenly

RE: Sparking brushes of Synchronous Motors

Do you have a bad diode in the field supply?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Sparking brushes of Synchronous Motors

(OP)
Like I mentioned in 1st thread, Only one machine has the problem, Other work fine.

RE: Sparking brushes of Synchronous Motors

what epete said + out of roundness of that slipring + slipring loose on the hub

Muthu
www.edison.co.in

RE: Sparking brushes of Synchronous Motors

A former employer used to have problems with some sliprings arcing.  The sliprings were exposed to a somewhat corrosive atmosphere and had tiny little surface pitting.  They started re-facing the sliprings with a different metal.

Another client had problems with only one brush of the two on one slipring arcing.  The problem was that the installer had not installed a jumper to equally share the current between the two brush-holders.

Another problem surfaced when we found that an ambitious electrician had "re-sized some off the shelf brushes from generator exciter service to make them fit the synchronous motor application.  After all, it was "all black carbon, right?"  Wrong composition=arcing.

 

old field guy

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