Question

A 400 V,50 Hz, six-pole three-phase induction motor drives a constant load of 140 N.m. The motor has the following parameters
?1=0.294 Ω
?1=1.39 ??
??=41 ??
?2′=0.156 Ω
?2′=0.74 ??

1) Starting.
Calculate the following:
i) Motor starting current.
ii) Motor starting torque.

2) Maximum operating point. Calculate the following:
i) Slip at which maximum torque is developed.
ii) Maximum torque developed.

3) Steady-state operation.
Calculate the following:
i) Motor slip.
ii) Motor speed.
iii) Motor current.
iv) Motor power factor.
v) Motor input power.
vi) Motor output power.
vii) Motor efficiency.

4) Speed control of the induction motor:
We need to control the speed of the load by controlling the speed of the induction motor using the ?/? method. The load should be driven at 700 rpm at the same slip obtained in part   3-i above. Calculate the following:
i) The source line-line voltage and frequency.
ii) Motor current.
iii) Motor power factor.
iv) Motor input power.
v) Motor output power.
vi) Motor efficiency.

vii) The line voltage control method can not be used here to reduce the motor speed to 700 rpm, Why? Fully explain your answer.

Notes:
- For calculation:
▪ Use the recommended IEEE equivalent circuit.
▪ Use five decimal digits.
▪ Make sure all equations and numbers are clear.

What is missing?

Answer 1