Universal motor is the special purpose machine that have a special feature that it can operate on both nature of supply DC as well as AC supply. is used to convert electrical energy into mechanical energy. Universal motor is used to perform high speed operation. In this article we will learn its construction and working principle.
Construction
Universal motor consist with two important part stator and rotor . Stator is the stationary part of motor that remains fixed at one place while the rotor is rotating part of the motor. Copper winding is placed on the stator core. We use copper material for winding due to their good electrical conductivity. Just like stator, copper winding is also placed on the outer portion of rotor. commutator and brush assembly remain connected with the rotor winding that placed on the stator pole is called field winding and that winding which placed on the outer portion of rotor slots is called armature winding.
in case of universal motor filled winding and armature winding both are connected in series. Core of stator and rotor are laminated, we provide lamination to reduce eddy current loss where lamination is the arrangement of various thin strips that joined together to make core of the machine.
working principle of universal motor
when we give DC supply to the stater winding then constant magnetic field produces due to DC current and inductive winding. Since DC current is frequency less so magnetic pole will be constant. And field winding is connected in series with armature so same current will flow in the armature winding . So according to the working principle of DC motor, whenever current carrying conductor placed in magnetic field , conductor experiences a force in tangential direction
so here also current flowing in the armature winding that placed in the constant magnetic field so torque acts on the armature winding and armature starts to rotate. According to direction of current torque will act on the armature. So this is first condition where Universal motor is operating on DC supply now we talk that how this motor will operate on AC supply as well.
when we give single phase AC supply to the field winding of Universal motor then due to AC nature of current and inductive winding changing magnetic field produces. Due to frequency in AC supply existing magnetic pole changes with respect to supply frequency.
suppose during positive half cycle of AC supply left side of a stator has North Pole (N) and right side of a stator South Pole (S) . In this condition direction of magnetic field will be from north pole (N) to South Pole (S) .
and direction of current in armature winding will determined according to direction of field flux. As you can see in the below diagram I have shown cross and dot , current flowing inward is represented by cross (×) . And current flowing outward is represented by dot (●) .
during positive half cycle (N-pole) is cross (×) side and (S-pole) is dot (●) side . In this condition torque will act on the armature in anticlockwise direction .
And during negative half cycle of AC supply field pole will changes now (N-pole) will right side ans (s-pole) will left side . And according to field pole , direction of current in armature winding will change . It means that when current is reversing then direction of magnetic field also changes and as well as direction of armature current changes according to field polarity.
And during negative half cycle of single phase AC supply same condition repeats like positive half cycle it means that , (×) & (N-pole) together , (●) & (s-pole) together. So direction of force on armature winding during negative half cycle will be same like positive half cycle. So armature of Universal motor will continue rotate with single phase AC supply. And you can check the direction of force using Fleming left hand rule. Thus Universal motor operates on DC supply as well as single phase AC supply.
Important points
- when we change the input terminal of Universal motor then motor will rotate in opposite direction
- in this motor when current get reverse direction of torque don’t changes torque always acts in same direction , that’s why it operates on DC supply as well as single phase AC supply.