Which of the following motor is self-starting?

Question

Question

This question was previously asked in

ALP CBT 2 Electrician Official Paper (Held On: 23 Jan 2019 Shift 3)

Answer 1

Three-phase induction motor is self-starting, because winding displacement is 120 degrees for each phase and supply also has 120 phase shift for 3-phase.
It results in a unidirectional rotating magnetic field is developed in air gap which causes 3-phase induction motor to self-start.
The single-phase induction motor is non self-starting in nature.
When single phase AC supply is given to stator winding of single-phase motor, it produces alternating flux i.e. which alternates along one space axis only.
It is not synchronously revolving (or rotating) flux, thus it cannot produce any rotation. Hence single phase induction motor is not self-starting.
To overcome this problem and to make the motor self-starting, it is temporarily converted into two-phase motor during starting.
For this purpose, the stator of a single phase motor is provided with extra winding known as starting winding in addition to the main winding. These two winding are placed across the single phase supply.