Page 725 - Basic Electrical Engineering
P. 725
4. The synchronous speed N , frequency f, and number of poles, P are related as
s
a.
b.
c.
d. .
5. When an induction motor is yet to start, i.e., at standstill, its slip is
a. 0
b. 1
c. infinity
d. near to 0.
6. The speed of a three-phase induction motor when supplied with three-phase, 400 V, 50 Hz
supply is 1440 rpm. The number of poles for which the windings are made must be
a. 2
b. 4
c. 6
d. 8.
7. A three-phase induction motor develops a torque of 500 Nm at normal supply voltage. If the
supply voltage is reduced to half, what will be the torque developed?
a. 250 Nm
b. 125 Nm
c. will remain constant at 500 Nm
d. 62.5 Nm.
8. The slip of an induction motor can be expressed as
a.
