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Time Constants Of Indution Motor

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Hello bonny


This varies considerably between motors as is reflected by the maximum Locked Rotor Time of motors.


The maximum LR time for some motors can be as low as 5 - 10 seconds, and others as high as 40 - 50 seconds.

To accommodate this variation, most good protection relays have a setting that reflects this value.


The cooling time constant is likewise very variable and is dependent on whether the motor is running or not. While it is running, there is additional heat input, and additional cooling compared to a stationary motor.


Best regards,


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  • 3 weeks later...

From what I know, the cooling time constant is the time required for the motor to cool down to ambient temperature from hot.

This information is not critical to motor protection but maybe required as a input to the motor protection module you are using. This cooling time constant can be obtained from your motor manufacturer.


It can be something like 60-120mins depending on the design.



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