The type of single-phase induction motor having highest power factor at full load is

The correct answer is "option 4"

Explanation: 

• We know that a capacitor is used to improve the power factor in any circuit i.e., it tries to decrease the phase difference between current and voltage applied.
• In a capacitor-run induction single-phase induction motor, the capacitor is connected across auxiliary winding during the running condition and always connected there permanently.
• From the above choices, only the capacitor-run motor has this property.
• So, Capacitors run single-phase induction motors have the highest power factor at full load.

Additional Information

Single-phase induction motor

• It is a type of motor that has two winding aligned at 90 degrees with each other connected single phase A.C. power supply.
• Since the flux of the motor is canceled each due to the double-revolving field theory.
• Its starting torque is zero, so this motor is not Self Starting.

To make this motor this motor Self Starting, the motor is divided the into following categories-

Types of single-phase induction motor:​

​​1.  Capacitors start and run type​

• This motor has a cage rotor, and its stator has two windings namely the main winding and the auxiliary winding.
• . The two windings are displaced 90 degrees in space.
• The motor uses two capacitors CS and CR. In the initial stage, the two capacitors are connected in parallel. 

2.  Capacitor run type

• These motors have a cage rotor, and its rotor consists of two windings namely, the main winding and the auxiliary winding.
• The single-phase induction motor has only one capacitor C which is connected in series with the starting winding.
• The capacitor C is permanently connected in series with the starting winding.
• The capacitor C is permanently connected in the circuit at starting and running conditions.

​

3.  Capacitors start type

• The capacitor-start motor develops a much higher starting torque, i.e.  3.0 to 4.5 times the full-load torque. ​
• To obtain a high starting torque, the value of the starting capacitor must be large, and the resistance of starting winding must be low.

​

4.  Split pole type

• The split-phase induction motor is also known as a resistance-start motor.
•  It consists of a single-cage rotor, and its stator has two windings.
• The main winding and a starting (also known as an auxiliary) winding.
• Both the windings are displaced by 90° in space like the windings in a two-phase induction motor.
• The main winding of the induction motor has very low resistance and high inductive reactance.

Important Points