What is Capacitor Start and Capacitor Run Induction Motor?

In this topic, you study Capacitor Start and Capacitor Run Motor – Theory, Construction, Diagram, Working, & Torque Speed Characteristic.

Capacitor Start and Capacitor Run induction Motor uses two capacitors (C₁ and C₂) for starting, one of them (C₂) being cut out for running by means of a centrifugal switch (S) when the motor reaches about 75 to 80 % of the synchronous speed. Fig. 1(a) Schematically illustrates this type of motor.

Fig. 1: Schematic representation of a capacitor start and run, single-phase induction motor.

Torque Speed Characteristic of Capacitor Start and Capacitor Run Motor

This type of motor has better starting and running performance with improved power factor. Fig. 1(b) shows the typical torque speed characteristic for such a motor.

Fig. 2: Typical torque-speed characteristic

Features of Characteristic of Capacitor Start and Capacitor Run Motor

1. Better starting torque i.e. 2 to 4 times the full load torque.
2. Better power factor.
3. Low maintenance.
4. Cost is somewhat more than resistance split phase motor.

Applications of Characteristic of Capacitor Start and Capacitor Run Motor

1. Drilling machine
2. Lathe machine pump
3. Refrigerator
4. Compressors
5. Air conditioner.

This motor has a higher starting torque. It is available upto 5 HP. The cost of the motor is more.