Answer / sudhakar

in star line voltage is equals to root three times of
phase voltage
due to this the effective voltage applied is less so the
current drawn by the machine is less in star than in delta

Answer / s.k sahoo

to reduce the starting current. is it ok?

Answer / sunil kumar sinha

^.^ KV motors are generally star connected because
insulation of winding of motor and interturn insulation is
much less because voltage across each turn in star winding
is much less (root three times) than the windings of delta
connections.
If 6.6 KV delta motor is to be manufactured the insulation
level will be much higher between turns as well as winding
as it will experience voltage level of 11 KV STAR MOTOR.
tHE SIZE OF MOTOR WILL BE BIGGER BECAUSE OF HIGH INSULATION
THICKNESS IN THE WINDING AND IT WILL BE COSTLY ALSO.

Answer / k.atchuta rao

generally at the time of starting any FOR induction motor
we need to have less starting CURRENT. at the same time we
need high starting torque. in motors the relation between
torque and current is (TORQUE IS DIRECTLEY PROPESNALL TO
SQUEREE OF THE CURRENT)WHILE REDUCING STARTING CURRENT AT
THE SAME TIME WE NEED TO MAINTAIN TORQUE IN A COORECT
VALUE. IF U USE STAR CONNECTION AT THE TIME OF STARTING IT
WILL REDUCES STARTING CURRENT TO 1/3 AND STARTING TORQUE TO
1/3. BECAUSE OF GIVEN MOTOR IS SMALL RATTING THERE IS MUCH
NO DIIFFERENCE OF REDUCING STARTING TORQUE WITH RESPECT TO
CURRENT

Answer / dd

As per Industrial practice, it is mandatory to run motors
greater than 200kW at medium voltages. These motors are
star connected to reduce voltage across each phase winding
to 1/root3. This reduces burden on the winding insulation
as starting time is longer.

Answer / fahri

Say My Transformer is 11/6.6kV Ynd11 and the Motor is Star
Connected. Would this approach be safe for my Motor that is
connecting the Delta of the Transformer to the Star of the
Motor.

Answer / mayur

FOLLOWING MAY BE THE REASON.
1. REDUCE THE STARTING CURRENT

JUST LIKE STAR / DELTA STARTER USED FOR CERTAIN MOTORS TO REDUCE THE STARTING CURRENT. THE APPLIED VOLTAGE ACROSS THE WINDING IN CASE OF DELTA CONNECTED MOTOR IS 1.73 TIMES THE STAR CONNECTED MOTOR. HENCE IN STAR CONNECTED MOTOR THERE IS A REDUCED VOLTAGE STARTING. SUBSEQUENTLY CURRENT IS ALSO REDUCED, HOWEVER THERE IS A SMALL EFFECT ON THE STARTING TORQUE SINCE TORQUE IS PROPORTIONAL TO SQUARE OF THE CURRENT WHICH MAY BE ACCEPTABLE.

ALSO SINCE LESS VOLTAGE IS APPLIED, THE INSULATION REQUIRED FOR HT MOTORS MAY ALSO REDUCE LEADING TO COST SAVING.

Answer / keyur lakhani

because,in 6.6kv we reqiure high starting torque so that we use star connection and also line voltage=root of 3 *phase volage
and also in this motor we connect more load so current drawn by this motor is high so we reduce by star connection

Answer / shri..

Because when starting the motor takes high inrush current.

We can use delta connection but before that star connection
required (Star/delta starter)

Answer / saksh

In delta connection line voltage is egual phase voltage so
inrush current will be high in motor phase, due to this
star coneection is used to reduced the starting phase
current.

An 8 pole, 50 Hz, 3-phase IM is loaded to a poing where pull out torque will occur. The rotor resistance per phase is 0.3 ohm and motor stalls at 650 rpm. The rotor frequency at maximum torque point is A 3.33% B 4.44% C 5.55% D 6.66%

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