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Try Google. Why do you think this will save energy?

When the motor is designed to run in delta connection, you cannot change the configuration to star connection. You will lose the motor torque and subsequently, your motor winding will overheat and burnt down.

There is no such thing by converting the motor from delta to star connection and thinking that you can save energy. If your motor is rated at 2KW the energy consumption will remain at 2KW whether you run your motor in Delta or in Star connection.

actually energy saving may occure since delta connected motor draws 1.782 * I, where I is the current drawn per phase in case of Y connection. By this way, the loss over the resistance between motor terminals and the utility can be reduced by a factor of three. In this calculation, it is assumed that Δ connected motor winding per phase sees the same voltage as Y connected motor winding per phase.

Oh my goodness, what are you thinking?

Torque in an AC motor varies by the square of the effective winding voltage. So if you take a motor designed for Delta connection and connect it in Star with the same terminal voltage, the effective winding voltage drops to 58% (1/1.732). So torque is therefore reduced to .58 x .58 = 33% of rated! The mechanical power rating of a motor is a function of torque and speed. Changing the connection does not change the speed, so if you reduce the torque by 67%, YOU REDUCE THE OUTPUT SHAFT POWER CAPABILITY OF THE MOTOR BY 67%!

So unless your LOAD is reduced by 67%, the motor will overload and stall, hence the "burn up" mentioned above. If your load is reduced by 67% from the original design, you simly have too large of a motor! While it is also true that a motor will only consume as much power as the load requires, minus efficiency, connecting n Star, even if the load is reduced to 67% of normal, is NOT as efficient use f motor power as simply reducing the size of a motor. Peak efficiency in a motor is achieved at 75% loading or greater.

Taking the 2kW example then, if you connect it in Star (assuming it was designed for Delta), it becomes a 0.66kW motor. If your load were reduced to only requiring 0.66kW, and the motor was left in Delta, the efficiency would probably be no more than 3% lower than if it were more fully loaded (typical numbers). If you take that same motor and connect it in Star, you can theoretically recover that 3%, but here is the rub. You have left ALL of the motor mass and inertia in the system! So what appears to be 3% savings on paper ends up as maybe 1 to 1.5% when all is said and done. With the same 0.66kW loading, a .75kW motor will be 88% loaded and operating at peak efficiency, so because you have also now reduced the mass and inertia of the motor itself, you have truly gained that efficiency.

Please do not post what you do not know about, it confuses people.

Dear JRaef,

Thanks for your brief information about the topic. the concept I mentioned is misunderstood as it is seen from your answer. The assumption is: " voltage per phase winding of delta connected stator is same as the voltage per phase winding of star connected stator." I looked at the topic from the view of power distribution. Moreover, it is also thought that there is a resistive drop per phase between the motor terminals and the utility. And, with the mentioned assumption, same shaft torque can be supplied in both connection.

Thanks for your true info but please do not judge before carefully reading.

Dear J Raef!!

Thank you very much for your reply. It was very inflormative and detailed.

So basically you want to convey is that replacing a underloaded motor with a small optimum sized motor would give more efficiency as comparec to a motor converted in star mode.

There is one more point regarding the - Mass and Inertia Left in the system when a motor is converted to star and there are then bound to be certain losses that reduce the efficiency gain in the motor.

Can you please elaborate this - Mass and Inertia of the motor and what are the losses and how they reduce the efficiency.

Please its a request and it will greatly add to my knowledge and help me deliver better.

Regards

Rooney