Answer / murali

At the time of starting motor current will be high .Need to
reduce the starting current for protection of winding in
motor. Since star connection reduce the current ratting at
starting condition so we use the star connection after
normal speed the motor will run in delta connection as
normal current

Answer / abhishek goyal

We use star delta for mostly above the 10hp motors (we use
dol starter). When we connect dol starter to above 10hp
motor it will be trip because it take high current during
starting time approx 6-7 times of rated current. If we using
star delta starter it will work because in star Iph=IL and
Vl=Vph/1.732 so that in starting time it take less voltage
then delta and it torque also less and speed also less as
per electrical or practical application at that time torque
is 1/route3rd or 1/1.732 time so that current also less by
1/route3rd or 1/1.732 times. After getting speed it will
connecting into the delta position.

If directly connected with supply it will burn out or damage
of some other electrical equipment because of high
current.insulation of motor also damage or burn.

Answer / gopala rao yalagala

Star delta conection 3ph sq induction motors above 10 hp motors at the starting time of taken the motor high torque so star conection produce high current minium 10 seconds motor running the star conection ofter taken the normal current because delta conection

Answer / ashresh

when start the motor high currents getting it can be damage of motor but that we use star delta connection to the motor

Answer / abinash

3 phase squirrel cage induction motor above 10hp with load and DELTA connected will takes high starting current due to starting torque.When motor start with star connected it takes low current but not reach to its rated efficiency.For this purpose motor above 10 hp started with star and after few second when starting torque reduced it will shifted to DELTA to achieve higher efficiency with control FLC and without loss.

Answer / suresh ram

10 hp or Above motor take starting current 6-7 times to normal current. To reduce current used star few times the after moto will be run delta the give be full efficiency.

Answer / rupam dwivedi

reduse the starting current@starting torque

Answer / sivakumar

first answer is two or three fluxs(torqres) are required for the to rotate the motor and to produce emf in the generator that why we r using three winding connected like star and delta.but single phase motors also used in small applications .and second answer is to reduce the stating speed of the motor .

Answer / ravi chaurasia

Dear Murlali, i would have been totaly agreed with u if the
qestion would have been : why we use star delta starter ?

We all know any induction motor works on the principle of
mutual induction ie when a 3 phase supply applied to stator
winding, 3 phase flux is set up in the air gap which links
with the rotor winding and it induces an emf in the rotor
winding and causes a current to flow in the rotor winding
and in responce to that rotor tries to oppose the every
cause which produces rotor current ie three phase rotating
flux and in responce to that it starts rotating.
Now if motor is not connected either in star or delta it
will not be able to produce 3 phase rotating flux in the
air gap and hence they are either connected in star or
delta.

Answer / rakesh

star delta connections r used to reduce the numb of
conducors required for pow transmission. Generally we gen
3ph pow, so there vl b 3 coils in generator 2 gen 3ph pow &
each coil vl have 2 point ie. start & end terminals of
coil. so totally 3*2=6 conductors r req to transmit pow
which increases the transmission cost, so in order to
avoid this v use star delta

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