replacement of ht motor

[ram14375]

Dear sirs,

we have two identical slip ring induction motor of 11kv,2100 kw,137 amps ,rotor voltage 1160v ,1105 amps started by seperate LRS used for driving ball mill. The average operating kw of the motor is around 1900kw.The required ball mill starting torque is around 150% of rated trq.

 

we have another slip ring induction motor of 1900kw ,134 amps,rotor voltage 1425v,805 amps rotor current .

can we use the above motor to substitute one of the running motors . If so what will be the impact on electrical and mechanical side. can anyone help

thanks

ram

[jraef]

You will need the torque-speed curves of both motors to be able to determine that accurately. My guess would be yes, but that is an expensive retrofit to be done on a guess.

[chaterpilar]

i wont suggest it as the tolerance margin is very low.

 

chaterpilar.

 

 

 

 

"The true test of maturity is whaen keeping a secret gives you more pleasure than passing it."

 

Albert

[marke]

As these are slip ring motors, the speed torque curves are a function of the secondary resistance starter.

Therefore, provided that you use an appropriate secondary resistance starter for the new motor, there should be no problem.

The rotor voltage for the two motors are quite different, therefore, a different rotor resitance is required.

 

Best regards,

[FXWeaver]

You may need to reduce your ball charge volume, which will lower your motor power requirements.

 

At what % ball charge are you currently operating your mill?

 

Reducing the ball charge will reduce the available grinding power. You must then decide whether you want to reduce feed rate to the mill or settle for a coarser product at the current feed rate.

[ram14375]

Dear sirs,

Thanks for the reply. we are charging the mill for 100% .We can definitely reduce the mill charging. BUt how about the starting and running torque of the two motors. how much it will impact the mechanical side.

 

 

suppose we have a motor of 2650 kw with the same rotor voltage and torque can it be combined with the 2100kw.

ur suggestions pls

thanks

ram

[marke]

Hello ram

 

If you apply a suitable secondary resistance starter to the alternative slip ring motor, and the average load does not exceed the motor rating you should not have any problems. This is because the rotor resistance determines the start current and torque curves.

The peak torque will probably reduce with the motor size reduction, but if you are currently operating at 150% maximum torque, this will not cause a problem with the smaller motor.

The running torque of the smaller motor will be lower as torque is a function of power and speed. If you reduce the power at a constant speed, you will reduce the torque by the same amount.

 

Please clarify what you mean by combining the 2650KW and the 2100KW motors.

 

Best regards,

[ram14375]

dear sirs

thanks for your response

Regarding the 2650 kw motor my question whether we can use one 2100 kw and 2650 kw motor of same rotor voltage.

thanks

ram

[marke]

Hello ram

 

I am still not sure what you are trying to do with the two motors.

If the motors are of different ratings, but the same rotor voltage, you will need to have different secondary resistance starters as the rotor current will be different.

 

If you wish to operate both motors driving a common shaft, then yes this can be done, but you would want to be sure that the secondary starters are designed to provide torque slip curves which match for each stage, and to synchronise the stage switching.

Does that answer your question??

 

Best regards,

[ram14375]

Thanks marke for your reply,

we have got two identical motor of 2100kw for driving the ball mill.We dont have an identical spare for the same.So we are palnning to expediete the possibility of running themill (in case of one 1900kw motor failure) with the other available (1900 kw or 2650 kw) motors.

 

These (2100kw) motors are started through LRS (common) and gets short cktd.We dont operate in intermediate steps.

Since the LRs is common we cannot vary the concentration of the electrolyte as it will the motor starting torque( in case of two different motors).My query is if we have a 2650 kw motor of same rotor voltage as 2100kw ,can we combine the motors(2100 and 2650 kw).how will be the starting torque in this case for 2100 and 2650 kw motors when started through a common LRS and how about running condition(the motors will be short ckt -no intermediate steps)

Thanks

ram

[marke]

Hello ram

 

The reactances of the two motors (2100 and 1650KW) will be different, therefore with the same impedance, the torque will be different. I can not comment on how this will perform with both motors onto the same resistor bank, but the optimum values at a given slip will be different.

I expect that one will do most of the work in this case.

 

Best regards,