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Motor Nameplate


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I know this matter has been discussed many times here. I have on site a motor of 30 k W which nameplate shows how to connect the motor in both star and delta connections. I wish to know if the power output is derated by connecting it in star.



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Hello Bob


If the motor is designed to operate on your supply voltage with a delta connection, then it is designed so that the correct flux is in the gap with line voltage (phase to phase) across each winding.

If you connect it to the same line voltage, but in the star connection, the voltage across each winding will be reduced by root 3 and so the flux will be reduced. This reduction in flux reduces the torque capacity of the motor, so it must be de rated to one third of the delta rating.

If you increase the voltage by root 3, then you must connect in star to prevent the flux being too high. With the increased voltage and star connection, the flux will be the same and thereofre the motor rating would be the same.


Best regards,

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