A 15 kW, 415 V, 4-pole, 50 Hz delta-connected motor gave the following results on test (voltages and currents are in line values):
No-load test |
415 V | 10.5 A | 1,510 W |
Blocked-rotor test | 105 V | 28 A |
2,040 W |
Using the approximate circuit model, determine:
(a) the line current and power factor for rated output,
(b) the maximum torque, and
(c) the starting torque and line current if the motor is started with the stator star-connected.
Assume that the stator and rotor copper losses are equal at standstill.
Hint Part (a) is best attempted by means of a circle diagram. For proceeding computationally from the circuit model, we have to compute the complete output-slip curve and then read the slip for rated output.