Answer / ashli

induction motors are of two types- squirrel cage and phase
wound motors. in squirrel cage motor as the rotor
conductors are shorted by endrings its not possible to add
additional resistance.but we can limit the current by
reducing the supply voltage at starting. here the high
current inrush is limited by star-delta starter.ie at the
instant of starting the stator winding is connected in star
der by voltage per phase becomes V/(3)^.5.. after the rotor
attains sufficient speed the stator windind is made delta.
in phase wound type motor the rotor condutors are shorted
through resistors. and current is limited by applying
resistors
synchronous motor is not a self starting one. syn motor is
made to rotate at syn speed firstly only then 3 p supply is
given to the armature. so no question of high current arises

Answer / lovkesh arora

Whenever you start a big heavy electric motor, you need to
start it slowly to prevent the rotor overheating and
drawing an enormous current. When the windings of a 3-phase
motor are connected in STAR the current is reduced to only
root three of the normal running current that is taken when
it is connected in DELTA.
Once the motor picks up speed, the connection is changed to
DELTA so that the motor runs at full speed and torque from
then on. It's a bit like using the gears of an automobile.

Answer / priyadharsini

types of starters in ac motor
1. Rotor resitance starter-it is used only for Slip ring
in squirrel cage IM is wound rotor so we cant add external
resistance.in starting resistances are included to limit
the starting current.
2. star delta starter-at the time starting the rotor is
connected as star and in running itis connected as delta.
it can be used for both slip and Squirrel cabe IM.
3. Auto transformer starter- at the time starting by using
auto transforme the voltage is reduced.
4. DOL starter - it doesnt reduce any staring current. it
is used only for small rating of motor

Answer / l.veeraragavan

Normally starting current of induction motor is 6 to 7
times of the full load current.This because high
inersia(mass) of the rotor.So more current require to
move this rotor.So if we insert he resistance in series
with ckt (in starting only, after starting we gradually cut
this resistance from Ckt) ,we can reduce this starting
current. i.e The function of the starter is inclde
resistance during,after starting it will gradullay cut the
resistance.

Answer / venu

Mainly starters are used to reduse the starting
current.normally we will use the star delta starter for the
above 7.5HP.

as per the electrical formula.

motor will start in star first
since IL = IPh
coz we have to equilize the starting current

then its go to delta

Since VL= Vph

Finally

In star -Current equal
In Delta- Voltage equal
that how the starter will control the startingcurrent

Answer / jaggu

Induction motor is similar in action to a poly phase transformer with short cktd secondary which is rotating. if normal voltage is applied to the motor then the motor will draw a large current at the start. Induction motor when directly switched on takes 5-7 times their full load current. This can damage motor winding and generate large voltage drop, which may affect other equipment operation. Therefore IM while starting uses following starters:
1) Direct online starter
2)Stator resistance starter
3)Auto transformer starter
4)Star-Delta starter and
5)Rotor resistance starter- only in the case of slip ring IM

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