WYE---Delta

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Wye Or Delta pertains to the winding connection of Stator and that of stator and rotor in wound Induction motors.Soft starter in simple terms slowly and in a programmed manner increases the applied voltage so that starting current is limited and Finally full voltage is reached .This normally used in cage induction motors.With Inverter drives also have this feature.whre sped variation is not required soft starter is used.

Current is proportional to voltage applied and the speed difference( Stator- rotor). Initially the difference is maximum and also the voltage full and so the high current.

Either we have to keep the difference minumum and is not possible as it has to start from rest.

Only way is to keep the voltage low and keep on increasing so the current is not high.

This is called soft start and hence less load on electrical and mechanical parts( Torque ia maximum initially)

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Good luck.

Normally when a High Powered Motor is started, the Starting Torque is very high (Normally it is 400-500% of the Full Load current) and this can burn the coils. Hence a system called Star-Delta Starter was being used, where-in, when the motor is started, the Starter takes up the Load in the Star position which is designed to take up the high torque and reduce the torque getting transferred to the motor. Once the Motor RPM picks up with the slow distribution of the current from the Star Starter, it has to take up more load from the Star Starter. But due to its design, the Star cannot feed more to the Motor to maintain its RPM and Load. Hence the Delta Starter takes over [This is normally termed as the Change-Over of the Motor] and gives in more load to the motor to do its loaded work.

But this change-over [which is a mechanical means] was not very delicate or the failure rate of the mechanical means was high, Electronic/Motorised control starters were introduced, wherein the Change-over was more efficient and accurate.

Some 3-phse induction motors are available with 6 leads.

There is one winding per phase and both leads for each winding are brought out to the wiring box. 3 phases x 2 leads per phase = 6 leads.

The terms wye and delta refer to the way the leads are connected.

Wye means that one end of each lead is connected together making a shape of the letter 'Y' and the 3-phas power is applied to the remaining other end of each lead. For 480 VAC power, the voltage acros each winding in the wye configuration is 277 volts instead of 480 volts and the motor is "soft started" with less than full voltage across the windings. (277 = square root of 3 x 480)

Delta means that each winding is connected together to form a triangle and that the full 480 VAC is imposed on each winding. This is the normal connection for a motor and each winding sees the full 480 VAC and the motor runs at design parameters.

What hasn't been said yet is that to "soft start" a motor in this manner requires a wye-delta motor starter that includes contactors to do the switching of the lead arrangement and timing to determine how long the wye configuration is used before switching to the normal delta configuration.