Induction Motor Questions

An induction motor is one of the most popular motors in the industry. Its simple construction makes it one of the most useful motors that finds its applications in our homes as well as in industries. Given below are the top 10 Induction Motor Questions.

Describe the Basic Construction of an Induction Motor

An induction motor is composed of a rotor, known as an armature, and a stator containing windings connected to a poly-phase energy source. Learn complete construction here.

What power factor does Induction Motors present to the line?

Induction motors present a lagging (inductive) power factor to the power line.The power factor in large fully loaded high speed motors can be as favorable as 90% for large high speed motors. At 3/4 full load the largest high speed motor power factor can be 92%. The power factor for small low speed motors can be as low as 50%.

Also learn Induction motor power factor and efficiency relationship here

What does slip indicate in an Induction motor

The term slip in Induction motors is used for representing the relative speed of rotor with respect to magnetic fields.

What is a mathematical formula for slip in Induction motor

What is the difference between Squirrel cage rotor and wound rotor induction motor

The rotor of a cage rotor that comprises of series of conducting bars laid into slots that are carved in factor of rotor and shorter at either end by the sorting rings. Since the overall setting looks squirrel exercise wheels the name squirrel cage is referred. On the other hand a wound rotor comprises of complete set of three windings that are mirro image of stator windings. The ends of rotor wires are tied to slips rings on shaft of rotor.

What is the condition for maximum starting torque in an induction motor

The starting torque in induction motor will be maximum when the rotor resistance/phase equals to standstill rotor reactance/phase.

What do you mean by plugging in an Induction motor

The term plugging refers to the rapid stoppage of 3-phase induction motor by simply interchanging the two stator leads.

By interchanging stator leads the revolving field turns in the opposite direction to the rotor. This phenomenon is referred to as plugging. During plugging the motor serves as a brake and absorbs kinetic energy from the still-revolving field causing the speed to fall.

How 2-speed squirrel cage motor is obtained

Two speed squirrel cage motors have stator winding that may be switched through suitable control equipment for obtaining two speeds. One speed is half of the other.

For exmple an induction motor with 3000/1500 RPM speeds.

What are advantages of skewed slots in rotor of squirrel cage induction motor

By skewed slots we mean slots that are not parallel to shaft axis. Skewed slots rotor has following advantages:

  1. It reduces noise
  2. It reduces vibratio
  3. It increases starting torque
  4. It increased rotor resistance
  5. It reduces starting current

Why air gap between rotor and stator of 3-phase induction motor should be kept small

Air gap between rotor and stator of 3-phase induction motor should be kept small so that:

  1. Leakage reactance is as small as possible
  2. Mutual flux should be produced with minimum exciting current

Leave a Reply