Answer to Question #340903 in Electrical Engineering for Gotty

Question

A 2200-V, 50-Hz, delta-connected three-phase induction motor has a star-connected slip-ring rotor with a phase effective transformation ratio of 3.8. The rotor resistance and stand-still leakage reactance are 0.012-ohm and 0.25-ohm per phase, respectively. Neglecting stator impedance and magnetising current,

(a) determine the rotor current and the corresponding stator and line currents at the instant the motor is started with the slip-rings shorted (4.0 marks).

(b) if the maximum allowable current in the motor supply lines is 600 A, determine the external rotor resistance per phase required to achieve this requirement (6.0 marks).

(c) determine the full-load currents if the full-load slip is 3% (4.0 marks).  

(14.0 marks in total)