A 415V, 50Hz, 6-pole, three-phase induction motor runs at full load with a slip of 4%. Under these conditions, the electrical input power was measured using the two Wattmeter methods, the two readings being 47 kW and 25 kW. Given that the delta-connected stator has a resistance of 0.5 Ω per phase, the stator iron loss is 2 kW, and the mechanical losses are 1.5 kW, determine the:
- Synchronous Speed in Revs/Min
- Rotor Speed in Revs/Min
- Total input power
- Operating power factor
- Line current taken from the supply
- Stator copper loss
- Air gap power
- Rotor copper losses
- Useful output power
- Useful output torque
- Machine efficiency
The starting current of an induction motor is typically 6-8 times that of the full load running current. For large machines, this large starting current can cause significant problems to the surrounding network. Briefly describe three techniques that could be used to limit the starting current of large induction machines.