Working of universal motor:
i) Working of universal motor with DC supply:
* When the universal motor is fed with a DC supply, then current flows in the field winding, it produces an electromagnetic field. The same current also flows through the armature conductors.
* According to basic motor principle, when a current carrying conductor is placed in the magnetic field, it experiences a mechanical force and torque exerted on the current carrying armature conductors, therefore the rotor starts to rotate.
ii) Working of universal motor with AC supply:
* When fed with AC supply, current flows through armature and field winding. So current carrying armature conductors are in magnetic field experiences mechanical force and ultimately produces unidirectional torque, because armature winding and field winding are connected in series, they carry same current.
* Hence, as polarity of AC voltage changes and current reverses its direction, the direction of current in armature conductors and magnetic field in the air-gap reverses at the same time.
* The direction of magnetic field and the direction of armature current reverses in such a way that the direction of force experienced by armature conductors remains same.