Problem with slip ring motor

[jammyjim]

What could be the possible causes of the following slip ring failure, the middle ring (of 3) has been getting extremely hot and fusing the brushes in thier holders, when this first happened new slip rings were made, and the brushgear was completely overhauled, the stator and rotor test ok

The same thing has happened again after a month, the liquid starter has been tested and is ok, any thoughts........?

I will get nameplate details if they will help, the stator is 6.6kv and rotor 2kv, and it drived a pump

It has been suggested that the brushes are sticking in thier holders, causing a bad contact between brushes and slipring, but after being overhauled the brushes passed through the boxes fine

Worried about overhauling the brushgear agian and the same problem happening after a month......

 

[Marke]

Hello jammyjim

This is either a mechanical problem such as sticking brushes or incorrect brush material, or there is an electrical problem in the resistor bank.
I would monitor the currents during start and run on the three rotor leads and see if they are normal.
I would also check the insulation between the rings. If there is leakage through the insulating material, that will heat up the whole area.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[edison123]

Looks like brush problem.

Check the chemical environment in which the brushes work. Chlorine, ammonia etc. tend to attack the brushes changing the brush characteristics. Better to contact the brush manufacturer than brush supplier/dealer for suitable brush grade and brush dimensions.

 

[stephenw22]

Have you had a chance to properly break-in the brushes? When new brushes or slip rings are installed, they should be broken in to allow for the best performance. It takes a little while to develop a nice patina on the slip ring.

Brush overloading or low relative humidity can also lead to brush failure.

I've never confirmed this, but I've also heard from a few electricians that spraying a little glycol on the slip rings will help them break-in better and more quickly.