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Repulsion - Induction Motor and Servo Motors

Repulsion - Induction Motor

The repulsion Induction Motor has a single phase Stator Winding but it has two separate Windings on Rotor in common slots. The inner Winding is a Squirrel cage Winding with the rotor bars permanently Short Circuited.

Place over the Squirrel cage Winding is a repulsion Winding is similar to a DC Armature Winding.

The repulsion Winding is a connected to a Commutator on Which ride short - Circuited brushes.

Repulsion Induction Motor
Repulsion Induction- Motor

When the motor starts the squirrel cage Winding due to its high Reactance has no effect and the motor starts as a repulsion motor giving high Starting torque.

As the motor picks up speed, the squirrel cage Winding comes in to action. The shifting from the repulsion to the Induction Motor characteristics is thus done without any switching arrangement.

Both of the Armature Winding are active during the entire period of operation.

The starting torque is about 2.25 to 3.00 times of the full - load torque, the lower being for larger Motors and the starting Current is 3 to 4 times the full-load Current.

The chief disadvantage of this type of motor are high cost, careful maintenance and tendency of sparking.

This type of motor is used for application requiring a high starting torque with an essentially constant running speed.

The common sizes are 1/6 to kw although Larger sizes are made. A common application is the air compressor.

Servo Motors

The motors which respond to the error Signal abruptly and accelerate the load quickly are called the servo motors.

The torque inertia (T/J) ratio is an important figure of a servo motor because the load is to be accelerated by it abruptly.

The fundamental characteristics to be sought in my servo - motor are :

  • The motor output torque should be Proportional to the Voltage applied to it (i.e., control Voltage developed by the amplifier I n response to an error Signal).

  • The direction of the torque developed by the servomotor should depend upon the instantaneous polarity of the control Voltage.

Servo motors are two types namely DC Servo Motors and AC Servo Motors.

AC servomotors are generally preferred to DC servomotors except for use in very high - Power System.

For very high power System DC Motors are preferred because they operate more efficiently than comparable AC servomotors.

This enables them to stay cooler. An Efficient motor also prevents excessive power waste, although power waste is generally not a prime concern in servomechanisms.

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