In star connection motor is taking low current and produce
high torque and in delta connection motor is taking high
current and low torque.to start the motor from stand still
condition we requeired high torque so first motor should in
star connection and then it should have conti. with delta
A star connected motor takes less current compared to a
delta connected motor since the phase current is 1/sqrt3
times the line current, but torque developed by the motor is
affected, since starting current is heavy in order to reduce
the heavy inrush current we place a star delta
starter.....so tat starting current can be comparitively
small...the reason for shifting to delta connection(after
motor attains 80% of the rated speed)is the power output of
the motor wil be 3 times the output wen it is connected in
star.....it doesn;t mean tat the m/c 3 times more efficient
than star connected one..but correspondingly the power drawn
by the motor also increases.........
comments r welcome....
actually we uses star and delta connections in a motor for
starting purposes,when the motor starts it will take high
current which effect to our power factor so to reduce the
inrush current we use the star/delta connections. in start
we get high tarque and less current which is our
requirments,in delta we get high current and less torque.
say a transformer is designed for 33/11kv step down with
ratio 0.33 for load 1 mva. if am giving 11kv as a input
that same transformer what will happen to its o/p voltage.
and whether it can be operated for 500kva