What is an AC Series Motor? Working, Diagram, Construction & Applications

The AC series motor is designed to work on AC and DC both. The stator is made of laminations of silicon steel to reduce the hysteresis and eddy current losses. The armature of the universal motor is the same as that of the ordinary series motor.

Figure 1: AC Series Motor.

Construction of AC Series Motor

An AC Series Motor is electrically almost similar to a D.C series motor. But there is a very slight difference in the construction of AC series motor and D.C series motor. The AC series motor, uses special metals in the pole pieces such as, silicon steel, which easily reverses its magnetic polarity without causing residual magnetism to remain after the reversal. Lamination is also done in AC series motor, in order to reduce the amount of eddy currents generated in the pole pieces. By the use of special metals and laminations in windings, the hysteresis and eddy currents are reduced. The AC series motor is shown in the following Figure 2.

Figure 2: Construction of Series AC Motor

In some large motors the compensating winding is used to improve the commutation. It is always connected in series with the field and the armature at the same time. High resistance brushes are employed to improve the commutation.

Working of AC Series Motor

Whenever supply is given, the current carrying conductors are placed in the magnetic field and a torque will develop to rotate in a particular direction. The direction of rotation can be changed by changing the direction of current in series field or in armature winding.

Generally, all AC series motors are provided with commutating poles to get improved commutation (as in case DC motors).

Advantages of AC Series Motor

The motor is simple, less expensive and generally used for lower ratings. It is used where high starting torque is required.

Disadvantages of AC Series Motor

1. Because of the high eddy currents produced due to the alternating flux, the efficiency of the motor is considerably reduced.
2. As the inductance in the field and armature circuits is high, power factor is low.
3. Starting torque is very less due to low power factor.
4. Due to high voltage and current induced in the short circuited armature coils in the commutation period, sparking takes place at the brushes.

Applications of AC Series Motor

The applications of AC series motor are as follows.

1. 1. They can be used in applications which require high speed.
   2. Due to high starting torque they are widely used for driving excavators, hoists, locomotives, electric traction.
   3. They can also be used to drive permanently connected load.
   4. It is used for sewing machine, table fan, vacuum cleaner, portable drill machines, blowers and kitchen appliances etc.