AC THREE PHASE MOTOR - Quiz

1) Which fault condition thermal overload relay protects A.C induction motor?

Short circuit Open circuit Over current Under voltage

2) What happens to the rotor of a 3 phase induction motor if its speed attains to synchronous speed?

Rotor speed reduces Rotor speed increases Rotor speed remains same Rotor bars get damaged

3) What is the effect of open circuit in rotor of an induction motor?

Motor does not start Over heating in motor Excess vibration of shaft Motor runs with very low speed

4) What is the reason for frequent blowing of fuse after motor running some time?

Improper earthing Over loading of motor Heavy voltage fluctuation Poor insulation in winding

5) What happens to a 3 phase induction motor, if one phase fails during starting?

Motor runs and stop immediately Motor runs in slow speed continuously Motor runs and draws more current Motor continues to run with irregular speed