star ,delta windings and motor relationship

3phase motors have usually two connection possibilities, star and delta. f.exe. motor rated 230V/400V has windings that can take 230V so when you have 230V supply you have to connect the motor in delta, connectin in star will not hurt the motor. But if you have 400V supply you have to make a star connection. If you connect this motor in delta to 400V you are giving each winding of the motor 400V but it can only handle 230V so the motor will burn.

Please notice that if a motor 230/400V D/Y is connected in triangel and supplied by a mains of 230V, this motor will burn !!!

The shaft load of the motor needs a certain amount of torque, this torque has to be deliverd by the motor. The motor will try to deliver the torque by pulling more current (ampères) out of the supply grid. So the current density (Ampères / square mm cupper wire) will be much higher. The motor will warm up and will burn.

Or a know motor shaft power needs a certain the electrical power.

The electrical power equals to 1.73 x U x I x cos fi.

If U decrease then I has to increase.

Because is STAR-Connection Insulation Level required low.Line Voltage-SQ.ROOt OF 3*PER PHASE VOLTAGE