Electrical Drives and Controls (EDC) MCQs | Page - 6

 the relative speed between rotor magnetic field and stator conductors is sip speed and hence the frequency of induced

 given a number of poles = 8. supply frequency is 50 hz. rotor speed is 720 rpm. ns = 120×f÷p=120×50÷8 = 750 rpm. s=ns-nr÷ns = 750 – 720÷750 = .04.

 the moment of inertia of the thin spherical shell can be calculated using the formula i=mr2×.66. the mass of the thin spherical shell and diameter is given. i=

 sinusoidal waveform is generally expressed in the form of v=vmsin(ωt+α) where vm represents peak value, ω represents angular frequency, α represents a phase difference.

 synchronous speed, ns=120×50÷4=1500 rpm. given a number of poles = 4. supply frequency is 50 hz. rotor speed is 1425 rpm. s=ns-nr÷ns=1500- 1425÷1500=.05. sb=2-s=1.95.

 the frame of an induction motor is made of cast iron. the power factor of an induction motor depends upon the air gap between stator and rotor.

 the slope of the v-i curve is resistance. the slope given is 5° so r=tan(5°)=.3443 ω. the slope of the i-v curve is reciprocal of resistance.

 when the number of stator slots is an integral multiple of a number of rotor slots the machine fails to start and this phenomenon is called cogging.

 supply frequency=50 hz. no- load speed of motor = 1000 rpm. the full load speed of motor=950 rpm. since the no- load speed of the motor is almost 1000 rpm, hence synchronous speed near to 1000 rpm.

 the inductor is a linear element. it only absorbs reactive power and stores it in the form of oscillating energy. the