Exercise 01
A three-phase hexapolar induction motor with a squirrel-cage rotor has the following characteristics: 230V/400V at 50Hz. The measured resistance of a stator winding is R1 = 1Ω. This motor is supplied by a 400V line voltage network at 50Hz.
1. Determine:
1.1 stator winding coupling (justify your answer).
1.2 synchronism speed.
2. At no-load, the motor runs at a speed close to the synchronous speed, absorbs a current of 4A and a power of 900W. Determine :
2.1 the stator copper losses at no-load operation.
2.2 the stator iron losses knowing that the mechanical losses pm = 452 W.
3.At rated load, the stator current is 10 A, the power factor is 0.8, and the rotor speed is 940 rpm. Calculate:
3.1 the absorbed power PA.
3.2 the stator copper losses at rated-load operation.
3.3 the transmitted power to the rotor PTr.
3.4 the motor slip.
3.5 the rotor copper losses at rated-load operation.
3.6 the useful power PU.
3.7 the motor efficiency.
3.8 the moment of useful torque.
Exercise 02
An induction motor with star-coupled stator winding is fed by a three-phase network at 400V line voltage and 50Hz. Each stator winding has a resistance R1 = 0.4 Ω.
During the no-load test, the motor rotates at a speed close to 1500 rpm, the power absorbed is 1150 W, the line current is I0 = 11.2A. A test with the rated load under the same voltage 400V gave the following results:
- Motor slip 4%
- Absorbed power 18,1 kW
- Line current 32 A
1. No-load test, find:
1.1 the stator copper losses
1.2 deduce the iron losses knowing that the mechanical losses are equal to 510 W (in this case we assume that the rotor losses are negligible)
2. Full-load test, find
2.1 power factor
2.2 rotor speed
2.3 rotor frequency for 4% slip. What can we say about the rotor iron losses?
2.4 stator copper losses
2.5 transmitted power from stator to rotor
2.6 mechanical power and deduce the rotor copper losses
2.7 useful power and motor efficiency
2.8 useful electromagnetic torque