The main adventage of using star-delta starter for
induction motors is as following-
if we start the motor with DOL(direct on line) or simple
starter the the motor requiers more current to start ,
which is 6-8 times the full load current.because the higher
tourqe is require to start the motor...
so in star-delta the motor is started in star, which
produce higher tourqe at lower current, means the starting
current is 4-5 times less than delta starting.
and then motor after start gets full speed and star
contecter is disconnect and motor runs in delta
connections.because torqe is less and lower current is
The main advantage is of-course the issue of starting current.In this case the starting line current is reduced to one third.Most importantly, starting torque is also reduced by the same amount.So pumps,motor-generator sets, where starting torque is not required to be high can take the advantage of star-delta starting.
But the problem is, this method is not adoptable for the motors which have high voltage rating(generally above 3kv).The reason behind:such motors are usually star-connected.We must have delta connection in the induction motor.
How the current is being reduced to 1/3 times in star/delta
starting. Can you please show it by derivation.
In my views power is reduced by 1/3 times and current and
voltage by 1/root 3 times. pls correct.