Rheostatic Control

You need to give the rotor voltage and current rating

k Tonys i got the formula the moment before you replayed as R2=V2/(1.732XI2).

so is there any theoretical approach to find secondary voltage and current of the rated IM to get maximum rotor resistance applied?

No, the turns ratio on the rotor governs the I & V to the sliprings. You need to look at the manufacturers plate.

Induction motor is a rotating transformer but i doubt the turns ratio is available with nameplate. I guess some alternative will be there.

The stator and rotor voltage and current will be on the makers plate. The ratio doesn't matter just the actual figures.

Is this a genuine question or hypothetical or homework?

The question is neither hypothetical nor homework.I want to find it for mere understanding.The catalogue of motor is not available because its too old and if i should get then i have to search in a mess. The nameplate details on the motor is to be checked again. Its on an EOT and the dust kills me on each climb. Stay in touch.

While you're on the crane have a look at the resistance bank rating plate and save us having to do the work!!

I never know you are very unavailable. I could not find any rating on resistance moreover we make resistance for the IM thats the reason i want to find exact value. If i didn't find they wont through me out.Its just a personal interest.

You say you want help but seem unwilling to help yourself. If the resistances are wound on site they must be done to a specification. Just ask whoever does the rewinding. It may be that the rewind is done by just simply measuring a length of resistance wire, measure the resistance of that length.

Other people have to climb to the motor, why can't you?