Question

The locked rotor in a 3 phase star connected 15 kW 4 pole 230 V 50 Hz IM runs at rated conditions of 50A. Neglecting losses and magnetising current the approximate locked rotor line current drawn when the motor is connected to 236 V 57 Hz is

1.

58.5A

2.

45.0A

3.

45.7A

4.

55.6A

Answer 1

Correct Answer - Option 2 :

45.0A

\(\begin{array}{l} {I_{se}} = \frac{V}{{{X_{se}}}}\ \alpha\ \frac{v}{f}\\ \therefore {I_{se}}\ nw = 50 \times \frac{{236}}{{230}} \times \frac{{50}}{{57}}\\ = 45A \end{array}\)