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In class we have a 3 phase asynchronous motor which says 400V delta 690V star. The nominal torque of the motor is 3,7Nm. Can the motor run safely nominal charged on 400V in star configuration?

I'm asking this because the nominal torque would be 0,7Nm which is lower than the nominal torque of 3,7Nm.The purple line represents the torque of the motor in star configuration.

enter image description here

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A 400 V delta / 698 V star motor can safely run continuously at 400 V with the star connection. However the motor should not be operated continuously stalled or with high slip. Operating stalled would mean that most of the input power would be dissipated in the rotor and the rotor would not be cooled as effectively at stall as it would be at normal operating speed. The same would be true to a lesser extent for operation at high slip.

The posted curves indicate that the motor is a high-slip design motor. As the load is increased, the slip increases and speed decreases fairly smoothly. That provides some protection against the motor suddenly "breaking down" and going rapidly from a fairly high speed to stall.

It seems like there would not be a good reason for operating a motor in this manner.

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  • \$\begingroup\$ Note: It is not clear what the words "nominal charged" mean in this context. My answer is based on omitting those two words from the question. \$\endgroup\$ – Charles Cowie Oct 13 '19 at 18:37

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