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Repulsion Induction Motor – Construction, Working, and Characteristics
In the repulsion induction motor, a high starting torque is due to repulsion motor action. When it is running, the repulsion-induction motor functions through a combination of repulsion motor and induction motor action.
Construction of Repulsion Induction Motor
The construction of a 2-pole repulsion induction motor is shown in the figure.
It consists of a stator which carries a single distributed winding fed from a 1phase supply. The rotor of the repulsion-induction motor has two independent windings placed one over the other.
The inner winding is a squirrel cage winding with rotor bars permanently short-circuited.
The outer winding is a repulsion commutator armature winding which is placed over the squirrel cage winding. The repulsion winding is connected to a commutator on which ride short-circuited carbon brushes.
The repulsion induction motor is not equipped with a centrifugal device and hence the repulsion winding works all the time.
Working of Repulsion Induction Motor
When a 1-phase AC supply is fed to the stator winding of the repulsion induction motor, the repulsion winding is activated since at starting the impedance of the repulsion winding is less than that of the squirrel cage winding. As a result, the motor is started as a repulsion motor with a corresponding high starting torque.
As the speed of the motor increases, the current shifts from repulsion winding to the squirrel cage winding due to the decreasing impedance of the squirrel cage winding with increasing speed. Therefore, under the running conditions, the squirrel cage winding carries the greater part of the rotor current. Consequently, the repulsion motor action is shifted to the induction motor action and it is achieved without any switching arrangement.
Form the above discussion, it is clear that the motor starts as a repulsion motor and when running, it functions through a combination of principle of induction (predominant) and repulsion.
Characteristics of Repulsion Induction Motor
The repulsion-induction motor has the following characteristics −
Due to the effect of repulsion winding, the no-load speed of the repulsion induction motor is somewhat above the synchronous speed.
The full-load speed of the repulsion-induction motor is slightly less than the synchronous speed.
The repulsion induction motors have speed regulation of about 6 %.
The starting torque of repulsion induction motors is 2.25 to 3 times of the full-load torque.
The starting current of repulsion induction motor is 3 to 4 times of the full-load current.
These motors are available in sizes 0.25 to 0.5 HP.
Applications of Repulsion Induction Motor
Repulsion induction motors are mainly used in applications requiring a high starting torque with essentially a constant running speed.
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