Electrical Engineering ⇒ Topic : Split phase capacitor start induction motor

Sachin
 
SPLITPHASE CAPACITORSTART INDUCTION MOTOR Another method of splitting the singlephase supply into two phases to be applied to the stator windings is placing a capacitor in series with the starting auxiliary winding. In this manner, the current in the starting winding may be made to lead the line voltage. Since the running winding current lags the line voltage, the phase displacement between the two currents can be made to approximate 90° on starting. The circuit of capacitorstart motor is shown in Fig.(a), while the vector diagram of the currents and voltage is shown in Fig.(b). The values of the angles shown are fairly representative, and are rounded off for convenience. One of the factors upon which the starting torque depends is the sine of the angle between the currents in the two windings. The value of series capacitor may therefore be reduced, while maintaining a phaseshift angle of about 900 .
Also it is seen that for the same magnitudes of field currents, the current I_{lr} is less in capacitorstart motor, because of the greater angle between the two field currents. In addition, the starting power factor is also better. For a given line current, the starting torque is thus much higher for a capacitorstart motor than for a splitephase induction motor. The starting torque of capacitor start motor is from 3 to 4.5 times the fullload torque, while that of splitphase resistance start induction motor rarely exceeds twice the fullload torque.
 
 
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