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while the starting current of motor is6 times higher than the rated current . can star contactor of half rating than main and delta can bear this high starting current ? what should we do ?
If you have motors 100kW, than main and delta contactors are 0,57*100kW and star contactor 0,33*100kW, use this simple formula and you will not make mistake.
It is a good practice that you choose contactors for one step higher in compare to calculation.
brother to start a motor it is depend on the the design ratio called starting KVA OR INRUSH then multiplied by the rated current that is the right and save starting current ,the code letter it should be mentioned in the name plate as a letter A or B or ...... V each letter has a number (sKVA / HP ) you can find the code table by searching engine
YES WE CAN RUN in star voltage is root of times current is line current to reduce staring current
in delta voltage i s line voltage current is root of three times
I THANK YES BECAUSE STAR CONTACTOR RTATED HI AMPER CURRENT AT SHORT TIM .
I think yes! Because STAR contactor current less than DELTA current in1,73 times. In Cirquit diagrams star-delta combination (any manufactures) determines STAR contactor less than DELTA one.
In star delta if a motor start we need double power to rotated as DOUBLE IN KILO WATTS.
at star delta connection there are three main contactors and a timer often
1_the delta power and it could be the main if it individual
2_star
3_and delta
4_timer
then when we supplying current the motor begin with a star
then after the adjusted time which means that the motor runs in steady state the two contactors of delta begin to work each of them carry the half current of star contacor
it's about the current that the motor draws at the end