> Auto transformer Starter can be used for both star/delta connected induction motors
> This type of starter can reduce the sudden fluctuation of current in the distribution system to the lowest level of all the different electromechanical types of starters.
> The taps on the autotransformer permit adjustment of voltage and motor torque.
> The taps provided on auto-transformers limit the starting voltage and supply motor in steps of 50% 65% or 80% of nominal voltage.
> Using an auto transformer for starting purposes the line current is always less than motor nominal current during start, because of the motor connected to the secondary side of the auto-transformer starter during acceleration.
> The tapping switches provided on auto-transformers limit the starting voltage and supply motor in steps of 50% 65% or 80% of nominal voltage.
> At the time of starting the motor is connected to the secondary winding of the auto transformer through tapping switches (ie, 50%).
> In this circuit there are three switches KM1, KM2 & KM3
> To start the motor keep KM3 open and close the switches KM1 & KM2
> As soon as you close the switches, the autotransformer supplies 50% of the supply voltage.
> The voltage supplied to the motor from the auto transformer is increased from 50 % , 65% and then to 80% of supplied voltage by switching the tappings.
> When the maximum voltage output is obtained from the auto transformer the motor is switched to direct voltage supply
> When the motor runs full load open KM1