Higher Current In Slip Ring I.M.

Have you checked the current/phase in running condition?

the current / ph of slip ring side is 14 amp during running.... and that of stator side is 60 amp/ph

As Vinu suggests check the rotor phase current, you will need a clamp meter that can record peak or average current otherwise due to the current pulsing with the "slip" you will not get a true reading. If you use average run the motor up to speed before using the meter. This will show any imbalance in either the rotor, cable or shorting gear.

Remove all brushes and IR test the rotor windings to earth followed by CR tests between rotor phases. You can't do an IR test between rotor phases unless you can get to the star connection, this would usually involve stripping the motor.

As an after thought are the brush grades the same? It won't be the first time mixed grades of brushes have been fitted to a motor.

the current is checked with clamp meter during running..the currents in all the slip rings are within limits... the brush grades are same... since it is heavy duty and continuous operation motor, stripping of motor will be the last option.....

hi,

greetings from India.

1. measure current at slip-ring side

- see weather it is balanced or not (within +/- 10%)

* check for contactor connection and contacts.

* check for value of resistance connected with that particular phase is damaged/burnt

* since Voltage is high w.r.t. current check insulation of cable for I.R. test.

* check for slip-ring Physically (blackening/ carbon formation )for that particular phase

* measure resistance of each rotor winding by good quality calibrated micro/ mili ohm meter.

Insulation of cable is fine... slip rings and brushes are replaced with new one to overcome this problem.. and as i said earlier grades are same...

hi,

sometimes while measuring currents for slip ring using clamp-on you may find variation.

measuring ohms(miliohm) and inductance of winding is perfect method to find out fault.

(use EMC Motor checker Equipment which is having R,L and IR measurement as well.

You have mentioned that slip ring current = 14 amp / Ph in running

that means slip ring resistances are in function during run operation.

generally at full speed slip rings are shorted.

what is exact operation of slip ring right from start to full run position?

for which application you are using this motor?

in which environmental condition it is running?

Please provide us correct measured values so that we can help you to get result, and You may get some idea.

hi aditya.... At starting full resistance banks come in circuit and in five steps these banks are cut off gradually one by one.. all this happens in appr 2 n half min. at the full load all the slip rings get shorted.

since the motor is connected to centrifugal pump and in continuous operation for sewage water pumping let's see if i could conduct test tomo, will let you know the test data by tomo.. see you bye

Do not take this to mean you should forgo all these other excellent suggestions, but one potential cause is a poor connection of the rotor winding to the slip ring. I have seen where soldered connections are cracked or broken.

i think i should check the rotor connection and winding by dismantling it. anyway thanx aditya, jraef, tony, vinu... meantime if u come across some solution pl revert... and i have posted the question anonymously (accidently).. so dont get confused i have posted this question initially...

Please check stator and rotor connections(line to line ) by electric motor checker instrument for percentage inductance and resistance values. This checking can be done without dismantling of motor assembly. For acceptable result,+/- 5% variation is O.K. Please check I.R. value (phase to ground/body )rotor resistance. Also please check rotor resistance by deploying Ohmmeter ( by injecting D.C. current, IR DROP method ). This checking may ascertain whether there is any crack in rotor resistances( incase of cracks, there will be fluctuation in resistance readings in high D.C current values ). Please check stickiness in contacts of rotor circuit contactors. This may cause temporary shorting of part of rotor resistancs during changeover from one step to other step causing short time high currents in rotor circuit which can't be detected by clamp meter. Since the motor application is for sewage pump, i.e in moist weather condition , it highly advisable that, when the motor is not in operation, the heater circuit must be in ON condition to avoid ingress of moistures, causing low insulation values.