AC Motor Questions

What is an AC Motor?

An AC motor converts alternating current into mechanical energy by using the principles of electromagnetic induction. An AC motor can be single-phase or three-phase. The important parts of an AC motor are the stator and rotor. The stator is the immobile part of the motor. The rotor is the rotating part of the motor.

Working Principle of an AC Motor

When the AC supply is fed to the rotor coil, it experiences some force. Torque will be developed due to this force in the clockwise direction that allows the rotor to rotate.

Important Questions on AC Motor

1) What is an AC Motor?

An electric motor that is driven by an alternating current (AC) is known as an AC motor. It generally comprises two basic parts, first an outside stationary stator coil to produce a rotating magnetic field having coils provided with alternating current, and second an inside rotor that is given a torque by the rotating field.

2) What are the advantages of AC Motors?

The advantages of AC motors are –

  • Its low cost
  • AC motors have a long life
  • Highly efficient
  • AC motors have large available ratings (to 1 MW or more)

3) What is a rotor?

The non-stationary part of a rotary electric motor is known as the rotor. The rotor rotates because of the wires’ arrangement and the motor’s magnetic field that produces a torque about the rotor’s axis.

4) What is a universal motor?

A type of electric motor that can function on either AC or DC supply is called a universal motor. An AC series motor or universal motor has armature field winds connected in series, similar to a DC series motor. Since the flux of field and armature current converse simultaneously, the direction of torque always remains the same, regardless of its polarity.

5) What are the types of 3 phase induction motors?

1. Squirrel Cage Rotor – It comprises a cylindrical coated core rotor with similar slots with copper in each slot. All the bars are permanently short-circuited with end rings, and no outside resistance can be added to the rotor conductors.

2. Wound or Slip Ring Rotor – It has a coated cylindrical core with homogeneously distributed windings. The end of the rotor windings is linked to three slip rings which can be connected to outside resistance through brushes connected to each slip ring. A starting torque can be obtained from this external resistance.

6) On what principle does an electric motor work?

The Motor Principle: when a current-carrying conductor is placed in an exterior magnetic field perpendicular to the conductor, a force perpendicular to itself and the external magnetic field is experienced by the conductor. This is the principle behind creating mechanical force by connecting an electric current and a magnetic field.

7) What is a DC motor?

A mechanical device that drives power from a direct current (DC) is called a DC motor. 8) State

8) Explain Fleming’s left-hand rule.

Fleming’s left-hand rule states that if you stretch your thumb, middle finger and forefinger of your left hand, such that they are perpendicular to each other, then the forefinger will represent the direction of the magnetic field, the middle finger will define the direction of the current, and the thumb will point out the direction of the force. Fleming’s Left-Hand Rule is applicable for motors.

9) What are the main parts of an AC motor?

The main parts of an AC motor are the rotor and stator. The rotating part of an AC motor is the rotor, and the stationary part is the stator.

10) What is the function of slip rings in an AC motor?

In an AC motor, a slip ring functions as an electrical joint for power transmission. It acts as a link between the stationary element and a rotating component.

Practice Questions

1) State and explain the working principle of the AC motor.

2) What are the different parts of electric motors? Explain their functions also.

3) Explain the construction of an AC motor briefly.

4) Differentiate between Fleming’s left-hand rule and Fleming’s right-hand rule.

5) What is the phenomenon of Electromagnetic Induction?

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