Starting a 4500 hp motor while it was coasting down 2

I work in a refinery. We recently inadvertently tripped a 12 kV circuit. The 12kV circuit was reclosed within 30 seconds. One of the loads on that circuit is a 4500 hp motor that is a driver for an air compressor. The motor has a breaker for a starter. The motor's breaker never opened during the outage. Its trip/close power is from the substation. Thus, one of the loads that was picked up as soon as the breaker was reclosed was the 4500 hp motor. When the tripped circuit was re-energized the motor was still coasting down. The motor's normallly runs at 1800 rpm. At the time the breaker was closed it had coasted down to 450 rpm. My questions are, should I change the motor control circuit so that upon loss of main power to the motor to trip the motor? If so/or not so why?

 

[itsmoked]

I don't understand how you can have ANY damage if there is no electrical phase problem. Why would a coasting start even be AS hard on a motor system then a full start? Isn't the back emf going to automatically limit the rotor heating and inrush? Why would there be one iota of "key shearing"? I would think any motor would be delighted to have a running start. I would think you could have 100 restarts an hour that are 20 cycles from the power loss.
AS LONG AS THERE IS NO RESIDUAL VOLTAGE. Would someone please explain why this would be wrong.

 

[Marke]

The only issue that I am aware of on restarting a rotating motor, is the interatcion of the supply voltage and the generated voltage of the motor. Provided that the generated voltage from the motor is insignificant, then there is no problem restarting a rotating motor. (except on a VFD!)
Typically, the voltage generated by the motor will decay in less than 1 second, it is a function of the rotor time constant and this varies from motor to motor. I expec that the new "High Eff" motors will have a longer time constant due to the lower rotor resistance.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[jraef]

Yes, but it is still a very short time, maybe 2 seconds at most?

horsedragon,
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