A three phase motor will give three times the power output when the stator windings are connected in delta than if connected in star, but will take 1/3 of the current from the supply when connected in star than when connected in delta. The starting torque developed in star is ½ that when starting in delta.

1. A two-position switch (manual or automatic) is provided through a timing relay.
2. Starting in star reduces the starting current.
3. When the motor has accelerated up to speed and the current is reduced to its normal value, the starter is moved to run position with the windings now connected in delta.
4. More complicated than the DOL starter, a motor with a star-delta starter may not produce sufficient torque to start against full load, so output is reduced in the start position. The motors are thus normally started under a light load condition.
5. Switching causes a transient current which may have peak values in excess of those with DOL.

The 3-phase induction motors are of three types depending upon the type of rotor they employ namely

(i) Squirrel cage rotor

(ii) Wound rotor or slip-ring

(iii) Double squirrel cage rotor induction motors. The principle of operation is same for all types of induction motors.

This is the basic principle of how induction motors work Video.
There is a lot more to say about motors, as starter winding with steady capacitor, multiple pole windings, three phases motor, etc etc, but the basic theory is this one !

Did you enjoy with this video ?
Did you learn something with this video?
Ok! I will ask you question about what you learnt.
what induction motor consist of ?

The idea of a rotating magnetic field was developed by François Arago in 1824, and first implemented by Walter Baily. 

Based on this, practical alternating current induction motors seem to have been independently invented by                          Nikola Tesla and Galileo Ferraris.

 Ferraris demonstrated a working model of his motor in 1885 and Tesla built his working model in 1887 and demonstrated it at the American Institute of Electrical Engineers in 1888(although Tesla claimed that he conceived the rotating magnetic field in 1882). 

In 1888, Ferraris published his research to the Royal Academy of Sciences in Turin, where he detailed the foundations of motor operation; Tesla, in the same year, was granted a United States patent for his own motor.

The modern system of a three-phase transformer and induction motor with a cage was invented by Mikhail Dolivo-Dobrovolsky in 1889/1890.

In this blog, my plan is to post what I’ve found useful,include some info,video,books,PPT...all about induction motor.

I hope you get benefits from our blog.

Posts by: Abdullah Al-ghamdi and Yazeed Alamri.