Construction and Working:
The construction of this motor is as shown in Fig.
It shows that the construction of this motor is similar to that of the split-phase type induction motor.
The auxiliary winding connected in series with the capacitor draws a leading current while the main winding continues to draw the lagging current.
Due to this, the fluxes produce a rotating magnetic field, which results in the rotation of the motor.
The construction of the capacitor start motor is as shown in Fig. The current (I1) through the main winding will lag behind the source voltage as the main winding is inductive.
But the current I2 through the auxiliary winding (I2) leads the supply voltage by some angle due to the presence of a capacitor. Hence the angle between the fluxes produced by I1 and I2 will be large.
Due to this large angle, the starting torque produced by the capacitor start motor produces a larger starting torque as compared to that produced by the split-phase induction motor.
As soon as the speed reaches 75% to 80% of the maximum speed, the centrifugal switch is automatically open-circuited and the auxiliary winding along with the capacitor goes out of the circuit.
The induction motor will then be running only on the flux produced by the main winding.
Phasor Diagram :
Fig. shows the phasor diagram of the capacitor start induction motor.
The main winding is inductive so its current I1 lags behind the AC supply voltage (V) by an angle Φ1.
The current I2 through the starting winding now leads V by an angle Φ2. This happens due to the presence of a capacitor in series with the starter winding.
Due to this arrangement, the phase angle between I1 and I2 i.e. α is very large. It almost approaches 90°.
Torque-Speed Characteristics:
Fig. shows the torque-speed characteristics of the capacitor start split-phase induction motor.
Due to the increased value of "α", the starting torque of this motor is higher than that of the split-phase induction motor.
At the speed N = N0 the centrifugal switch will be open-circuited and the motor will operate only on the main winding.
Applications:
They are widely used for heavy-duty general purpose applications like
1. Refrigerator units,
2. Air conditioners.
3. Compressors,
4. Jet Pumps,
5. Centrifugal Pumps,
6. Conveyors,
7. Fans.
8. Blowers etc.