Question 3
(a) List three parts of an alternator.
(b) A 4-pole, three-phase inductor motor is connected to a 415 V, 50 Hz three-phase supply. Calculate the:
(i) percentage slip when the motor is running at 1450 rev/min.
(ii)motor speed when the slip is 6%
OBSERVATION
The expected responses were:
(a) Parts of an alternator.
- The main winding (stator).
- The Rotor.
- The slip rings and the carbon brushes.
- Field winding.
- Poles.
- Yoke.
- 4-pole, three-phase inductor motor, 415 V. 50 Hz three-phase supply.
- percentage slip when the motor is running at 1450 rev/min,
synchronous speed of the motor
Ns = 1500rev/mins
The fractional slip; S
or Slip =3.33%
- motor speed when the slip is 6%
Some of those who attempted this question listed 3 parts and did some of the calculations correctly while others did not. Many did not put the unit for each answer.