I have a motor which is designed for 3 phase, 380V. The power rating of motor is 132kw and motor stator winding is connected in delta connection. If I connect the same motor stator winding in star connection with same 380 V line voltage, what will be the impact on motor line current and power rating of the motor.

  • \$\begingroup\$ Is this homework? \$\endgroup\$
    – Transistor
    Commented May 15, 2019 at 5:52

1 Answer 1


When you connect it in a star configuration, the voltage across each of the stator windings will be reduced by \$\sqrt3\$ and correspondingly, the peak mechanical power that could be delivered to a load for a given slip and supply frequency will be lowered significantly.

So, for a comparable slip, the current and voltage will both be reduced by about \$\sqrt3\$ and hence the power delivered to a load is reduced by about 3.

  • \$\begingroup\$ On top of that, the PEAK torque capability of the motor is reduced by the SQUARE of the voltage reduction. So instead of having just 58% of the available peak torque, you will get 33%. Peak torque is what a motor uses to re-accelerate after a change in load, or to accelerate it from a dead stop. Reducing it by 2/3 usually results in stalling unless the load itself is reduced by that amount or more. \$\endgroup\$
    – JRaef
    Commented May 16, 2019 at 0:11

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