A 3-phase, 460 V, 1740 rpm, 60 Hz, 4-pole wound-rotor induction
motor has the
following parameters per phase: R1 = 0.25 Ω, '
2R = 0.2Ω, '
1 2 X = X = 0.5Ω, 30 m X = Ω.
The rotational losses are 1700 W. With the rotor terminals short-circuited, find:
1. at starting:
• current when started direct on full voltage,
• a torque
2. at full load:
• ratio of starting current to full-load current
• power factor
• internal efficiency and motor efficiency
3. maximum torque and slip at this torque
4. how mach external resistance per phase should be connected in the rotor
circuit so that maximum torque occurs at start?