Slipring Motor Brushes

Yo Guest,

We experienced something similar on the brushes of the swing generators of P & H draglines.

It was also extensive wear , nothing specific to see or even feel.

I dried the brushes we had in stock , it was high humidity in our case.

Maybe it is something like it at your place as well ?

Good luck T L.

how brushes can be dried?

Looking at your problem there may be following reasons

1. Holder pressure is too high

I think regarding Holder pressure, it will be OK.

2. Temperature inside Carbon brush compartment is not to the desired value

I think problem is on the temperature of Carbon Brush compartment side. Carbon brush wear increases either the temperature increases/decreases up/down a certain band. e.g normally there is a heater installed inside this compartment to maintain a certain temperature and to control the humidity. In our case (4300 KW, 6300 V, 50 Hz, Y, 457 A, P.F 0.89, 995 RPM) compartment temperature normally remains between 45 -60 C. In either case whether the temperature is below 45 C and above 60 C, wear rate increases

2nd check the ventilation fan (internal cooling fan) is working. Check the filter inside of the compartment are working properly. If air filter are not working normal they are also going to disturb the temperature inside the compartment.

Air regulation is very necessary. either a flow sensor or differential pressure is installed for this purpose. In case of abnormality (air flow)it stop the motor.

We also face the same problem and change the filter and problem get solved.

Please send some information like

1. History of this motor (Before this problem some event)

2. No of Cooling fans

3.Thermostate setting

4. Full nameplate of motor and manufacturer

also what do you mean by this

"we replaced the motor with a motor with the same characteristics .but new motor brushes also were grinded in 48 hours."

Please share with us your finding

Waiting for ur Reply

1#4000kw 995rpm 6.3kv 442amper rotor voltage 1620 rotor current 1477 p.f.0.86 manuf.by ABB

2# no event before that explaned]

3#no thermostat

we have two mills with same motors we replaced the motor by similar motor of the other mill and new motor had the same behavior in this position

to know:we have ordered a set of RC53 brushes and are going to start motor with new brushes

"by visual check it seem that brushes are of two type but all of them are marked the same and supplied by the motor supplier"

Was wear rate same on all brushes

Are both motors are from the same manufacturer?

hi

we uncoupled both motors of mill and start them with new brushes that were bought recently (yesterday). after 3 hours of working operator stopped the motor because mentioned motor windows were coverd by brush powder.wear rate was very high 8_14 mm in 3 hours .the other motor of mill was normal. we dismantel all parts of brushgear and cables to starter and insulators and.....after checking and washing, parts were reassembled.we start motor and after 12 hours of working behavior was acceptable, know mechanical group is coupling the motors.incidentally motor is air cooled with 3 fans on motor shaft 1#circulation of cooling air in cooling pipes 2#slipring area fan 3# stator area fan also we put pt100 in slipring area and during latest working slipring area temp. was about 24 degrees centigrade.

Now what is the condition of the motor. Is it now working normal.

Is problem on the motor starter side.

Please Don't forget to tell your experience regarding this problem

NOW AFTER 100 HOURS OF WORKING MOTORS ARE WORKING NORMALLY AND WEAR RATE IS ACCEPTABLE DUE TO MAINTENANCE MANUAL OF MOTOR.WE THINK THAT DIRTY AND WEAK INSULATORS CAUSES CURRENT LEAKAGE AND THIS WILL PRODUCE HEAT AND HEAT WILL INCREASE WEAR RATE OF BRUSHES.

WAITING FOR UR IDEA....

Thanks for sharing the result and be a part of discussion up to the solution of the problem

What does the motor manufacturer say?

I would suspect that the fault is not in the motor, but in the starter/speed control circuitry. The Guest has stated that they have replaced the suspect motor with a similarly rated motor, and the new motor shows the same problems. I would carry out a thorough check of all the motor, and starter connections, and double check those that were disconnected during the original brush maintenance, to ensure they have been replaced in the correct position. I know a 4Mw motor is a big beast, but if possible, and the motors are running in tandem, with the same control gear, I would look to change over the starting/speed control circuitry, to see if the problem moves to the other motor. This would isolate the problem to either the motor, or control gear.

hi

we think that it was a mixed problem first bad brushes and then current leakage.at first we checked starter and connections and we have no speed control.