Question

1. The rotor resistances per phase of a 4 pole, 50 Hz, 3 phase induction motor are 0.024 Ω and 0.12 Ω respectively. Find the speed at maximum torque. Also find the value of additional resistance per phase required to develop 80% of maximum torque at starting.​

Answer 1

Answer 1

S=R2/X2

gives Sm=0.2

speed = Synchronous speed*Slip

N=300rpm

Tst/Tm=2R2*X2/(R2^2+X2^2)

0.8= 2a/(1+(a)^2)

where a=X2/R2

gives Rext= 0.156Ohm