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The capacitor-start capacitor-run motor is a type of single-phase induction motor. The capacitor-start capacitor-run induction motor is also known as ** two value capacitor motor**. The schematic diagram of a capacitor-start capacitorrun induction motor is shown below.

The capacitor-start capacitor-run induction motor consists of a squirrel cage rotor and its stator has two windings, viz. the **starting** or **auxiliary winding** and the **main** or **running winding**. The two windings are displaced by an angle of 90° in the space.

This motor uses two capacitors − the **starting capacitor**
*(C _{S})* and the

In order to obtain a high starting torque, a large starting current is required. For this, the capacitive reactance in the starting winding should be low.

Since the reactance of the starting capacitor is given by,

$$\mathrm{𝑋_{𝑆}=\frac{1}{𝜔𝐶_{𝑆}}}$$

Hence, for *X _{S}* to be small, the value of starting capacitor

During the normal operation of the motor, the rated line current should be smaller than the starting current. Therefore, the capacitive reactance of the running capacitor should be high and is given by,

$$\mathrm{𝑋_{𝑅} =\frac{1}{𝜔𝐶_{𝑅}}}$$

Hence, for *X _{R}* to be high, the value of the running capacitor

As the motor attains the normal speed, the starting capacitor *(C _{S})* is disconnected from the motor circuit by a centrifugal switch (S) and the running capacitor

The phasor diagram of the capacitor-start capacitor-run motor is shown below. At starting both the capacitors are in the circuit, therefore, the phase angle φ is greater than 90°. When the starting capacitor *(C _{S})* is disconnected from the circuit, then the phase angle becomes 90° electrical.

Following are the primary characteristics of a capacitor-start capacitor-run induction motor −

These motors have quiet and smooth running operation.

They have high efficiency.

These motors produce constant torque and not a pulsating torque.

Because of the constant torque, the motor is vibration free.

The capacitor-start capacitor-run motors are used for driving the loads of high inertia requiring frequent starts where the pull-out torque and the efficiency required are high such as −

Air compressors

Refrigerators

Pumping equipment

Hospitals, studios and at other places where silence is important, etc.

- Related Questions & Answers
- Capacitor-Start Induction Motor – Characteristics and Applications
- Permanent Split Capacitor (PSC) Induction Motor
- Repulsion-Start Induction-Run Motor: Operating Principle and Characteristics
- Capacitor Types: Fixed & Variable Capacitors
- AC Motor Types: Synchronous Motor & Induction Motor
- Difference between Synchronous Motor and Induction Motor
- Speed Control of Induction Motor
- Starting Torque of 3-Phase Induction Motor; Torque Equation of 3-Phase Induction Motor
- Three Phase Induction Motor Starting Methods
- Construction of 3-Phase Induction Motor
- Inverted or Rotor Fed Induction Motor
- Three-Phase Induction Motor Torque-Speed Characteristics
- Three Phase Induction Motor – Working Principle
- Construction of Circle Diagram of Induction Motor
- Running Torque of Three-Phase Induction Motor

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