Dear all
I have 60hp and 725rpm wound rotor motor on hand but without its external resistor bank which is used to start the motor without excessive current and also for speed variation.

my question is i need to build the resistor bank from scratch so i need to know the maximum resistor value that can be connected in series with the rotor winding for the motor with the above specification

 

Pictures of the motor nameplate or voltage and current specs for the motor will be needed.
At 600 volts it would take 75 amps to make 60 HP, if we neglected all losses. At 480 V it would take almost 100 amps.

You will need an industrial sized resistor bank to handle that power level (10's of kilowatts)

 

http://www.steadypower.com/products.php?product=Avtron-LPH-Portable-Load-Bank-(25%2d75kW)

Just for an idea of what you are seeking. You are somewhere around 50kw with the motor you have.

http://www.steadypower.com/categories.php?category=Load-Banks/Small-Portable-Load-Banks

 

http://www.hilkar.com/motorstartingandcontrolresistors.html

The previous post was for load banks and you said starting resistance. The industrial size and costs part doesn't change though, sorry

http://www.postglover.com/download/wound-rotor-motor-resistors/

 

The maximum resistance would be just below the point the motor stalls with no useful torque.
If you have any kind of resistor bank on hand, try the highest value, as the current wold be very low at this point, large wattage should not be required for test purposes.
Max.

 

here is the name plate data of the motor

star symbol delta symbol
prim 380V 220 V
89A 154 A
sec 340V 84.5 A

and the resistor is for the rotor winding. I mentioned something saying "is used to start the motor without excessive current and also for speed variation" which may be mistake as i read that wound rotor rotor resistor purpose may be for having enough torque at start up and off course for speed control.

and please also consider the maximum resistor addition (infinity) open rotor circuit will this harm the motor during start up

 

A wound motor with an open rotor circuit will produce NO torque.
The maximum torque occurs with a fully shorted winding.

 

and the resistor is for the rotor winding. I mentioned something saying "is used to start the motor without excessive current and also for speed variation" which may be mistake as i read that wound rotor rotor resistor purpose may be for having enough torque at start up and off course for speed control.
and please also consider the maximum resistor addition (infinity) open rotor circuit will this harm the motor during start up

If you are trying to find the maximum resistance try as per post #5 with heating element resistors etc to find the minimum useful torque, as mentioned the open circuit rotor will just present a high impedance choke to AC ,
Max.

 

in the case of squirrel cage induction motor if the rotor stops or slows down significantly then there will be a possibility of damaging the stator winding due to excessive current. but will this happen in this case say if i open circuit the rotor winding and hence motor stall and damage the stator winding ? this is what i am afraid

 

As in post #8, if the rotor is open circuit, the motor represents a high impedance to the AC supply, it also will not run.
This is what happens when you introduce a high resistance for low rpm, with very low torque.
Max.

 

Thank you all
so i will test the motor with a combination of industrial 3kw resistor heater, initially with maximum resistance gradually decreasing it