Q17/ A 1100V, 50HZ, delta-connected induction motor has a star-connected slip ring rotor with a phase transformation ratio 3.8. The rotor resistance and standstill leakage reactance are 0.0122 and 0.252 per phase respectively. Neglecting stator impedance and magnetizing current, determine (i) the rotor current at start with slip rings shorted (ii) the rotor power factor at start with slip rings shorted (iii) the rotor current at 4% slip with slip rings shorted 2 Tutorial Sheet (1) (iv) the rotor p.f. at 4% slip with slip rings shorted (v) the external resistance per phase required to obtain a starting current of 100 A in stator supply lines. Ans [1157A , 0.048 lag , 742.3A , 0.77 , 0.7072]

Q17/ A 1100V, 50HZ, delta-connected induction motor has a star-connected slip ring rotor with a phase transformation ratio 3.8. The rotor resistance and standstill leakage reactance are 0.0122 and 0.252 per phase respectively. Neglecting stator impedance and magnetizing current, determine (i) the rotor current at start with slip rings shorted (ii) the rotor power factor at start with slip rings shorted (iii) the rotor current at 4% slip with slip rings shorted 2 Tutorial Sheet (1) (iv) the rotor p.f. at 4% slip with slip rings shorted (v) the external resistance per phase required to obtain a starting current of 100 A in stator supply lines. Ans [1157A , 0.048 lag , 742.3A , 0.77 , 0.7072]