Electrical machine

It is advisable to avoid line-starting of induction motor and use starter because

• motor takes five to seven times its full load current

• it will pick-up very high speed and may go out of step

• it will run in reverse direction

• starting torque is very high

Rotor rheostat control method of speed control is used for

• squirrel-cage induction motors only

• slip ring induction motors only

• both (a) and (b)

• none of the above

If any two phases for an induction motor are interchanged

• the motor will run in reverse direction

• the motor will run at reduced speed

• the motor will not run

• the motor will burn

In three-phase squirrel-cage induction motors

• rotor conductor ends are short-circuited through slip rings

• rotor conductors are short-circuited through end rings

• rotor conductors are kept open

• rotor conductors are connected to insulation

In a three-phase induction motor

• iron losses in stator will be negligible as compared to that in rotor

• iron losses in motor will be neg¬ligible as compared to that in rotor

• iron losses in stator will be less than that in rotor

• iron losses in stator will be more than that in rotor

A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. onfull load. The machine has 6 poles. The slip of the machine will be

• 0.01

• 0.02

• 0.03

• 0.04

In the squirrel-cage induction motor the rotor slots are usually given slight skew

• to reduce the magnetic hum and locking tendency of the rotor

• to increase the tensile strength of the rotor bars

• to ensure easy fabrication

• none of the above

A 3-phase synchronous motor has 12-polesand operates from 440V, 50 Hz supply. If ittakes a line current of 100 A at 0.8 powerfactor leading, its speed and torque are nearly

• (A) 500 rpm and 1165 N-m

• (B) 1000 rpm and 2330 N-m

• (C) 500 rpm and 2330 N-m

• (D) 1000 rpm and 1165 N-m

Which of the following motors is used in mixers?

• Repulsion motor

• Reluctance motor

• Hysteresis motor

• Universal motor

A shaded pole motor can be used for

• toys

• hair dryers

• circulators

• any of the above