(a) List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque?
(6)
(b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate:
(10)
(i) The synchronous speed.
(ii) The speed of the rotor when the slip is 4 per cent.
(iii) The rotor frequency when the speed of the rotor is 600 r/min.
Reference Answer
### Part (a): Starting Torque of a Three-Phase Induction Motor **(i) Factors Determining Starting Torque** The starting torque of a three-phase induction motor is the torque produced by the motor at the instant of starting, i.e., when the rotor speed is zero and the slip is unity (s=1). The magnitude of this torque is determined by several key factors derived from the motor's fundamental torque equation: $$ T \propto \frac{s E_2^2 R_2}{R_2^2 + (sX_2)^2} $$
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