for reducing the motor starting current,initially motor
will take 4to 5 times of full load current,If we use star
delta it will reduce 1.732times of its torque as well as
current will reduce,motor will get safe

actually the main concept is to reduce the starting current.
initially stator windings are connected to the bus through
star connections it reduces the stating voltage to 1.732
times n hence the starting current.
after sometime ,when max.speed is achieved it has been delta
connected and the voltage applied at the terminals is equal
to phase voltage.

The concept of star delta starter is to reduce the starting
current of motor. in star connection line voltage and
pahase voltage is same which is 230v.so srating current
normally reduced.

Basically star delta starter is used to reduce the starting
current.When u'r connections are in star, the voltage is
reduced by 1/1.732 times.When the motor attains 80% of
speed, connections changed to delta.
praful nandankar

for an induction motor at starting current is very high
speed is small so initially reduced current is applied.for
star connected winding phase voltage is root3 times the line
voltage and for delta current is root3 times the line current
so initial current can be reduced by using delta and then
star during starting of the motor

At the starting motor needs high torque to reach rated speed
so it will required more flux to get that torque hence it
takes more current from the supply, but the winding
resistance is too low to withstand this current.

we know that
in star phase current = sqrt(line current)
In delta line current = phase current

So current is reduced by sqtt(3) times in star so motor is
first connect to star and then delta

Is This Answer Correct ?

16 Yes

14 No

Jagadisha.n. Bmsit

Other Electrical Engineering Interview Questions

Question

Asked @

Answers

what is the difference between power and distribution
transformer?

If a fan get trip and run in reverse direction due to
system flow. Now in this condition during starting how can
a VFD bring this negative speed to zero and later run in
forward direction?