Mainly Induction Motor takes 5-6 times of FLC while starting
in DOL mode.So soft starter is used to start the motor for
reducing starting current and smooth starting.Softstarter
which gives the voltage from 30% to 100% percentage of
voltage by certain time(Its in seconds) to the motor.By
means of thyristor softstarter is controlling the
voltage.After 100% voltage reached,the inbuilt DOL bypass
contactor is come into picture.
Advantages of softstarter:Motor life be good,Mechanical
equip life be good.
Disadvantage:It is mainly not applicable for heavy starting
for starting a rated motor with a DOL starter which draws 5-
6 times of load current initially which causes voltage
drops in line while a soft starter takes comparatively less
current and gradually decrease to the rated current.
but the main draw back of soft starter is its torque
remains low at the starting.
If the capacitor bank is installed in switchyard say
132/22kv then on LT side say 22kv/0.433kv is it necessary to
install capacitor bank for maintaining power factor. if pf
is maintained on HT side then will that be maintained on LT
side as well.if not then how&why??????/ please