Capacitor Start Induction Motor

CAPACITOR START INDUCTION MOTOR

Capacitor start induction motor is used to get higher starting torque. The capacitor is connected in series with the auxiliary winding as shown in fig 3.75. The starting current (Is) leads the line voltage, because of the capacitor present in the auxiliary widing. The running current (Ir) lags the line voltage. The phase difference between the two currents is approximately equal to 90° during starting. The phasor diagram is shown in fig 3.76.

Speed-torque characteristics

The auxiliary winding is disconnected from the circuit by centrifugal switch at 75% of the synchronous speed, (i.e) the capacitor is used during starting period only. The direction of rotation of the motor can be changed by changing the connections of one of the windings. The speed-torque characteristics is shown in fig 3.77.

Characteristics

 (i) The starting torque is 250 to 400% of the rated value

(ii) The breakdown torque is upto 350%

(iii) Power factor is 0.5 to 0.65

 (iv) Power rating is 1/8 to 1 HP

(v) The efficiency is 55% to 65%

Applications

(i) Compressors

(ii) Conveyors

(iii) Refrigerators

(iv) Pumps

(v) Washing machines