SOLUTION

• It depends on the construction of the motor if the armature winding is connected in series it will behave as a universal motor and we know that a universal motor can work on both AC and DC motors.
• If the armature winding is connected in parallel there won’t be a unidirectional magnetic field, the direction of the magnetic field, as well as the direction of the current in the armature, will be reversed in the second half of the AC cycle as a result, the motor either run slowly or won’t rotate.
• When an AC  supply is given to the DC series motor then there will be high inductance in field and armature circuits which causes a low power factor.
• With operation on alternating currents, the eddy current loss increases considerably. Hence in addition to the armature, the field structure has to be laminated.
• The D.C. series motor when connected to A.C. supply has a much greater tendency to produce sparking. Also, its power factor is very low which will lead to poor efficiency of the motor.
• Both excessive sparking and poor factor are prevented by compensating the motor, the aim of which is to neutralize the effect of self-induction. The armature is compensated by employing coils carrying the armature current and placed in such a way as to neutralize the armature flux. The compensating coil can be connected in series with the main field or can be short-circuited on itself.