in STARDELTA starters the mode(from star to delta) automatically changes after a specified time period..
MY QUESTION IS..
*when a motor is running in no load and if we use some controllers to make the (star delta)starter to stay in Star mode itself, can power be saved, as we are applying only 1/root(3) of the line voltage to the motor
*we can sense the load current and change it to delta once the motor gets loaded..
*because in industries the motor might not carry load at all the times.. so on no load we can switch it back to star and save the power ..
*pl tell me whether my concept will work. if this is correct i will choose this as my project..

Hello barani

Yes, you will reduce the iron losses when the motor is connected in star, but the transition from star to delta is normally an open tranistion and causes a major current and torque transient which can do damage to the driven load and create electrical interference.
You would be best to use a closed transition and there are additional losses in doing so.

Best regards,

Plus your mechanical load on the motor in Star would need to be 1/3 or less of the full load capacity in Delta, otherwise you will overload the motor in Star and no energy will be saved. Unless of course you count the fact that the motor has tripped off line as an energy savings!

hello jraef,
thank u very much for answering . i have a doubt.... u told "mechanical load on the motor in Star would need to be 1/3 or less of the full load capacity in Delta, otherwise you will overload the motor in Star and no energy will be saved. " how can we fix the cut off point as 1/3 of full load? pl give me derivations if any. it will be helpful for me.

Dear marke,
thank you very much for spending time for answering me.