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Question: What is A.C motor? Explain the construction and working of A.C motor.


A.C motor

 An A.C Motor is the machine that converts electric energy into mechanical energy. It makes use of alternating current (the direction of current flow changes periodically in the alternating current).

Construction of AC motor

An A.C motor has two basic electrical components; a stator and a rotor.


The stator is the stationary part of the A.C motor (The term stator is derived from the word stationary). It consists of a group of individual electromagnets arranged in such a way that they form a hollow cylinder.


Similarly, the rotor is the rotating electrical component of the A.C motor (Since it is rotating during the operation of motor, hence the reason for the name). The rotor also consists of a group of electromagnets arranged around a cylinder with the poles facing towards the stator poles. It is placed in the stator and mounted (fixed) on a shaft. The cylinder is made of laminated iron core.

Lamination is a particular technique of making some material in a number of layers or pieces. The new material thus formed is more stable and stronger than the one in a single layer. Usually some adhesive material (glue) is used for this purpose.

Working of an AC motor

The net purpose of this arrangement is to make the rotor rotated which in turn rotates the motor shaft to deliver the mechanical energy. This happens when an alternating current is provided to the stator; eddy current is induced in the rotor coils by the rotating magnetic field of the stator. The eddy current in the rotor produces magnetic fields which interact with the rotating field of the stator and exert a torque on the rotor and makes it rotated in the direction of the rotation of the stator B-field.

There are six magnetic poles on the stator and two on the rotor. See diagrams in your book. Let at time 1, the stator poles A-1 and C-2 are north poles and the opposite poles A-2 and C-1 are south poles. The south pole of the rotor is attracted by the two N-poles of the stator and the north pole of the rotor is attracted by the two south poles of the stator. At time 2, the polarity of the stator poles is changed (Remember we use alternating current in which the polarity changes periodically). Now C-2 and B-1 are north poles and C-1 and B-2 are south poles. The rotor is forced to rotate 600 to line up with the stator poles of opposite polarity (see the figure). At time 3, the polarity changes again and now B-1 and A-2 are north poles and B-2 and A-1 are south poles. The rotor moves by 600 once again. At time 4, when the polarity of the alternating current changes, A-2 and C-1 become N-poles and A-1 and C-2 as south poles once again. The process is thus repeated and the rotor is rotating continuously.

As the rotor is connected to the motor shaft, the shaft also rotates and drives the connected load.

Note: You can search for excellent pictures and videos of A.C motor on internet; some of them exceptionally good.


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