AC motor restart transient

Hello, my question is, when an AC motor is restarted before the rotor has come to a complete stop, can the motor restart transient current be greater that the motor starting current at rest. I know that is the rotor is still turning there is a voltage being generated in the rotor. The reason that I ask is, here in the US the National Electrical code mandates that a fire pump be able to withstand a restart transient of 24 times the motor full load current. I know that motors have different characteristics based on the design letter and code letter. This just seems excessive.

HerbThank you,

 


asked 2 months ago
Herb2
Herb

1 Answer

You could possibly have transients.  It depends on the system/motor characteristics and when any switching occurs. 

While not directly related to your problem, the following note on star-delta starting illustrates how you could analyze this and try various scenarios.  You restarting is not that far away from reconnecting the motor in delta

Note - motor star-delta starting

answered 1 week ago Steven McFadyen 238
Steven McFadyen

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