If we change three phase induction motor connection from delta to star . how it will affect power consumption?
by 
bhushan
ANSWERS: 3
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If we change the connection from delta to star then power consumption will come down. Because the rpm will come down by 8 to 10 due to low voltage. Conversion icreases the slip. we know the power is directly propotional to cube of the flow. P1/P2= cube of(N1/N2) = cube of (Q1/Q2) so flow will come down,thus rpm will come down so the power will come down. So the motor is derated by 1/under root of 3 so phase current becomes equal to line amps, hence the power factor is improved by this conversion. But mind it Sir! there are chances of burning of motor if the load on the motor is increased beyond 55 to 58%. We changed it in few of our motors, first we identified the motors which were running at less than 50% load, & the conversion was done only in the motors running at less than 50% load to avoid the risk of burning of motors.
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A MOTOR CAN BE CONNECTED EITHER IN STAR OR IN DELTA. BUT IT CAN BE DONE ONLY AFTER ANALYISING CERTAIN IMPORTATANT FACTORS. TORGUE(STARTING AND RUNNING),ACCLELARATION TIME,VOLTAGE DIP ETC.THAT IS WHY STAR-DELTA CONNECTION IS USED FOR MOTORS ABOVE 20 OR 25 KW MOTORS.IT ALL DEPEND ON WHAT IS THE DRIVING EQUIPTMENT .FURTHER IF A MOTOR IS RUNNING ALWAYS WITH 50% OR LESS THAN THE RATED LOAD ,IT IS A WASTAGE OF POWER DUE TO INCREASED COPPER LOSS LEADING TO POOR EFFICIENCY.HERE YOU CAN CHANGE TO STAR FROM DELTA PROVIDED STARTING AND RUNNING CONDITIONS PERMIT SO SUCH FACTORS SHOULD BE ANALYSED BEFORE CHOOSING THE CONNECTION OR CHANGING THE CONNECTION V.NATARAJAN NUMBAI
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IN DELTA CONNECTION THE CURRENT DRAWN FROM THE SYSTEM IS 1.732 TIMES OF THAT OF STAR CONNECTION.SO IN STAR CONNECTION THE LINE CURRENT IS EQUAL TO PHASE CURRENT.IT LEADS TO REDUCED COPPER LOSS HENCE THE POWER DRAWN WILL BE LESS THAN IN DELTA CONNECTION FOR THE SAME LOAD
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