is it magic relay

[sahafi]

Please I need your help if there is a relay can protect the motor feeder from tripping when we have any switching? Briefly, when the main feeder tripped all motor feeders tripped on that bus while the bus tie closed immediately to supply the subject bus from the other source. I have learned that there is a relay looking to the speed of the motor in certain speed the motor feeder will not trip and take its power through the bus tie. Am I right if yes what the name of this relay is? Thank you in advance for your help

 

[bennie]

Re: is it magic relay

The problem is not only the time between switching events but the synchronization of the sine waves. The incoming and the motor winding will not be in sync.

You are basically firing an out of sync sine wave from a generator, to another generator.

Check with motor control companies for ride through power equipment.

 

[templdl]

Re: is it magic relay

Sahafi, Bennie is right on.
A motor acts as a generator for a brief time when power is taken away and restored immediately restored. The power generated by the motor is out of phase with the restored power which appears as a short circuit to the OCPD. You have two choices, either an in phase transfer where you would have to anticipate an emergency loss off power which would make you a better man than most, or, you must put a slight time delay on the re-energization of power to the motors which would allow the counter "EMF" generated by the motors to settle down. This power transferring problem often occurs the automatic transfer switched the transfer so quickly, such as a contactor of stored energy breaker type, so that they cause an out of phase transfer. A time delay neutral (TDN) feature allows a brief delay between the transfer.
Because of the slower mechanical nature of breaker type transfer switches nuisance tripping of breakers seldom poses to be a problem.