Modifications are necessary in a dc series motor so that it operates satisfactorily on ac supply. The modifications are as follows:
1) AC series motor is built with a few field turns as possible in order to reduce series field impedance. 2) A.C series motor is provided with a large number of poles with less flux per pole. 3) The motor is provided with large number of armature conductors to compensate the reduced field and to develop the required torque. 4) The air gap is made very small because of weak field. 5) All parts of the magnetic circuit of an a.c series motor must be laminated to reduce the eddy current losses. 6) A.C series motors are designed to operate on low frequency, low voltage supply. 7) The armature coils are single turn coils and brushes of less width are used. 8) The compensating winding is provided in the pole faces of an a.c series motor to neutralize the armature reaction effect. 9) The motor is suitable for low voltage. It requires transformer to operate it. 10) Inter poles are provided for good commutation, high efficiency and high output. 11) Use of high resistance carbon brushes are made. 12) Width of brushes is kept small to avoid sparking.
Application of A.C Series Motor: 1) Electric traction 2) Stone crushing machine 3) Washing machine 4) Mixers and grinders 5) High speed vacuum cleaners 6) Sewing machines 7) Food processors 8) Drilling machine