Slip ring problems on Toshiba 6500kW WRIM 1

[ChiMike]

One of my clients has experienced failures on a Toshiba 6500kW, 11kV WRIM where a phase-to-phase arc destroys the slip rings during start-up. After the 1st failure, the mfg suggested that poor housekeeping (carbon dust build-up) and excessive start events contributed to the failure. Housekeeping was drastically altered when the spare motor was installed and the slip ring cabinet and surfaces are vacuumed prior to any restart of the mill. Motor starts will continue to be a problem as the site in west Africa experiences frequent, almost daily, power outages. The liquid resistance started serving this motor has been investigated for proper setup and is not believed to be contributing to the flash-over. Several months after the initial failure, the slip rings on the spare motor were destroyed by a phase-to-phase arc. Again, during motor start up.
Does anyone else know of similar problems with these motors?

 

[oftenlost]

I have a customer with a 4500 KW Toshiba that has suffered two failures in the ring assembly. The application is a cement finish mill, a TEWAC enclosure. I increased the creepage distance from the ring to rheostat buss by increasing the opening and enlarging the insulating feed through supports and was required to manufacture a new brush ring support insulator. I do not believe that this will cure the ring problem as I repaired the unit in kind due to time constraints. I feel that I will need to redesign the brush support system to increase the creepage distance on the ring assembly too. I do not believe that I have seen the last of this motor.

 

[edison123]

ChiMike

Cna you post a photo of the sliprings and the brush holder arrangement here ?



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

 

[ChiMike]

I have photos of the brush holders, but they're on a different computer. Will upload them tomorrow.

Geometry of the brushes & holders has been verified correct. Mass-loss of the brushes is also monitored closely and plotted over time with no outrageous degredation of the brushes. Spring force has been reduced slightly. Low brush temperature is thought to play a role and they have reduced the flow of cooling air into the slip ring cabinet.