The speed of a 300-V, 900-rpm separately excited dc motor is controlled by a three-phase full converter. Its field circuit is also controlled by a three-phase full converter. The field current is set to the maximum possible value and Rf = 150Ω. The ac source of both converters is a three-phase, Y-connected, 380-V, 50 Hz. The armature resistance is 0.25 Ω and the motor voltage constant is Kv = 1.25 V/A-rad/s. The viscous friction and no-load losses are negligible. Assume that the armature and field currents are continuous and ripple-free. a) If the motor is operating at rated speed and the load torque is 115 Nm, find the delay angle of the armature converter αa and the output power of the motor in horsepower. b) If the load torque and field current remain the same as part a) and αa = 0°, find the motor speed in rpm. c) For the same armature delay angle and load demand partb), find the delay angle of the field converter αf such that the motor speed is 1,500 rpm.
The speed of a 300-V, 900-rpm separately excited dc motor is controlled by a three-phase full converter. Its field circuit is also controlled by a three-phase full converter. The field current is set to the maximum possible value and Rf = 150Ω. The ac source of both converters is a three-phase, Y-connected, 380-V, 50 Hz. The armature resistance is 0.25 Ω and the motor voltage constant is Kv = 1.25 V/A-rad/s. The viscous friction and no-load losses are negligible. Assume that the armature and field currents are continuous and ripple-free.
a) If the motor is operating at rated speed and the load torque is 115 Nm, find the delay angle of the armature converter αa and the output power of the motor in horsepower.
b) If the load torque and field current remain the same as part a) and αa = 0°, find the motor speed in rpm.
c) For the same armature delay angle and load demand partb), find the delay angle of the field converter αf such that the motor speed is 1,500 rpm.
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