Question

Question:  The equivalent circuit of a 440 V, 3-phase, 8 pole, and 50 Hz star-connected induction motor is shown in figure 1. The short-circuit test is conducted with a locked rotor and a line current of 80 A. The open-circuit test is conducted by supplying the stator winding at rated voltage and at the rotor is rotating freely without any mechanical load.

           Fig. 1 The per-phase equivalent circuit of a 3-phase induction motor

a)  Determine the line voltage and power factor on the short circuit test;

b)   We need to apply a low voltage in a short-circuit test. What is the reason for using low voltage?  

                                                                                                              c)       Determine the line current and power factor on the open-circuit test;

                                                                                                                

d)  The electromagnetic torque if the motor is running at speed of 720 rpm.