What happens when AC supply is given to DC machines?

DWQA QuestionsCategory: DC Motor & GeneratorWhat happens when AC supply is given to DC machines?
ravi asked 6 years ago
3 Answers
dada answered 6 years ago
  • Considering we are giving AC supply to DC shunt Motor
  • We know that the shunt winding of DC shunt Motor has large number of turns so that it has appreciate amount of inductance.
  • When AC is applied to shunt motor inductive reactance of shunt winding reduces field current too much,c consequently shunt motor will not run on AC supply.
beu answered 6 years ago

When A.C. supply is given to a D.C. motor:
1)In case of Series connection of armature winding and field winding , it may run. 
2)But, In case of parallel connection , it won’t rotate at all and will start humming and will create vibrations, as a torque produced by positive and negative cycle will cancel out each other. D.C. motor will be heated up.

guma answered 6 years ago

Short answer: The motor will start rotating if it is a series dc motor. Otherwise it depends.
Long answer: A motor will only rotate if it experiences unidirectional torque. For a series motor the field winding and the armature winding are connected in series. Hence, even if the voltage or current polarity changes due to AC supply it happens simultaneously for both the winding. Now the torque produced in the dc motor is given below (in linear region of BH curve)
Now, it is clear that even if both of these currents change their direction the torque remains positive. So in series motor unidirectional torque is maintained and the motor continues rotating.
However, in shunt motor the impedance of these windings are different and being parallel connected in nature the current flowing through them is definitely going to be different with a finite phase difference in them. Thus it depends on the phase difference. Depending upon the phase difference the torque can be positive, negative or zero.
Therefore, it can not be stated explicitly for other motors (shunt or compound) without knowing their parameters.