ISM III YEAR

A 3-phase induction motor with its rotor blocked behaves similar to a _________

• transformer under short circuit of secondary terminals

• transformer under open circuit of secondary

• synchronous motor under slip test

• synchronous motor under open circuit

Mechanically air gaps in induction motor are kept very low to avoid _________

• lower power factor

• lagging nature

• magnetizing current

• all of the mentioned

The rotor of 3-phase slip ring induction motor is fed from a 3-phase supply with its stator winding short circuited having rotor rotating clockwise at a speed of Nr, then the _________

• speed of air gap field w.r.t. stator is Ns-Nr anticlockwise

• speed of air gap field w.r.t. stator is Ns-Nr clockwise

• speed of airgap field w.r.t rotor is Ns clockwise

• speed of airgap field w.r.t. stator is Ns-Nr clockwise

Starters are required in the induction motor because __________

• torque produced is very low at starting to overcome inertia

• they are not self starting

• of high starting current

• all of the mentioned

For the application requiring high starting torque and minimum starting current, the most suitable starting method will be?

• Star-Delta method

• DOL method

• Reactance starting method

• Auto transformer starting method

A 3-phase slip ring IM is has its copper bars changed by the aluminium bars in the machine. With the above change ___________

• starting torque remains same

• starting torque increase

• starting torque decrease

• maximum torque increase

If the resultant flux will not be in phase with the resultant mmf Fr. This is due to __________

• hysteresis effect

• armature reaction

• hysteresis effect and armature reaction

• eddy currents

The short circuit characteristic of alternator is a straight line due to __________

• no armature reaction

• no saturation

• no eddy current

• all of the mentioned

Potier method is very accurate due to __________

• emf and mmf are handled as AT

• emf and mmf are handled as voltage

• emfs are handled as voltage and mmf as AT

• none of the mentioned

Voltage regulation for an alternator operating at leading power factor is negative due to ___________

• magnetizing nature of armature reaction

• demagnetizing nature of armature reaction

• cross-magnetizing nature of armature reaction

• all of the mentioned