Induction motors week 14

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

• Starting torque is very high

• It will pick up very high speed

• Motor takes 6 to 7 times its full load current

• It will run in inverse direction

A change of 5% in the supply voltage of a 3 phase induction motor will produce its torque a change of approximately

• 7%

• 8%

• 9%

• 10%

A pump induction motor is switched on to supply 30% lower than its rated voltage. The pump runs. What will eventually happen?

• Get heated and consequently get damaged

• Start after sometime

• Continue to run at low speed without damage

• Nothing will happen

If the air gap of an induction motor is increased

• None of these

• The magnetizing current will increase

• All of these

• The magnetizing current will decrease

In an induction motor the torque is related with the supply voltage as

• T is proportional to V^ (1/2)

• T is proportional to V

• T is proportional to V^2

• T is for teen titans

In a double squirrel cage induction motor, the outer cage winding has

• High resistance

• Low resistance

• High reactance

• Low reactance

If the rotor slots are made deeper, the rotor resistance is

• increased under running condition

• decreased under running condition

• decreased at starting

• increased at starting

In a squirrel cage induction motor, the number of rotor bars is generally

• Prime number

• Odd number

• Even number

• None

For the same kVA rating, the leakage flux in induction motor is ____ that of transformer.

• None

• About the same

• More than

• Less than

The stator and rotor cores of an induction motor are made up of laminated sheets

• to reduce the hysteresis loss in the core

• to enable the stator and rotor cores dissipate heat more effectively

• to reduce the eddy-current loss in the core

• to make the rotor and stator mechanically strong