A **Capacitor Start Capacitor Run Induction Motor** is a single phase motor consists of a stator and a single-cage rotor. The stator has two windings i.e. main winding and an auxiliary winding. The auxiliary winding is also known as starting winding. In construction, these two windings are placed 90° apart in space. This motor has two capacitors i.e. C_{s} and C_{r}. This motor is also known as **Two value capacitor motor**. The Capacitor Start Induction Motor is shown in figure 1.

The capacitors C_{s} and C_{r }are connected parallelly during motor starting.

C_{s} = start capacitor

C_{r } = run capacitor

R_{m} = main winding resistance

X_{m}= main winding inductive reactance

R_{a} = series resistor connected in the auxiliary winding

X_{a} = auxiliary winding inductive reactance

S = centrifugal switch

## Working of Capacitor Start Capacitor Run Induction Motor

When the stator windings are energised from a 1-phase supply, the main winding carries current I_{m} and the starting winding carries current I_{a}. During starting, high torque is required. For high torque, a high current is required. In order to draw high current, the auxiliary winding capacitance reactance should be low. As capacitive reactance is given by

X_{s} = 1/(2πfC_{s})

To have low X_{s}, C_{s} should be large.

During normal working, the line current required is small. In order to draw low current, the auxiliary winding capacitance reactance should be large. As capacitive reactance is given by

X_{r} = 1/(2πfC_{r})

To have large X_{r}, C_{r} should be low.

The capacitors C_{s} and C_{r }are connected in parallel during motor starting. The value of the capacitor C_{s} is chosen such that current I_{m} is made to lag current I_{a} by greater than 90°. Therefore, there is a time-phase difference (α) and 90° space difference between the two currents. These two currents produce a rotating magnetic field which starts the motor.

When the motor reaches speed about 70 to 80 % of synchronous speed, the capacitor C_{s} disconnects from the supply by centrifugally operated switch S. The capacitor C_{r} is permanently connected to the circuit.

The phasor diagram for this motor is shown in figure 2. During starting, the phase difference is greater than 90° (α>90°) as shown in fig. 2(a). When capacitor C_{s }is disconnected, the phase difference is equal to 90°.

The torque-speed characteristic of this motor is shown in figure 3.

**Note:**

1. The reversal of the direction of rotation of this motor is possible by reversing the line connections of either main winding or the auxiliary winding. This can be done when the motor is at standstill condition.

2. The starting torque is high.

3. The motor has very less noise. Also motor runs smoothly.

4. These Motors are costly.

5. They have higher efficiency than motors running on main winding alone.

6. Start Capacitor C_{s} is short-time rated and has electrolytic construction.

7. Run Capacitor C_{r }is long-time rated and has oil filled paper construction.

## Applications

The **Capacitor Start Capacitor Run Induction Motor **is suitable for higher inertia loads where frequent starts are required.

1. It is used to pumps, refrigerator, air conditioner compressors, etc.