transition from Genset to Utility

[HighPotter]

Like to hear some ideas, if ya got em.

3phase 480v 200 hp well motor, operated via soft start controller. During the monthly back up genset test, when the transfer switch changes from generator back to utility, the motor shuts off. It then goes into a pre-set lock out at the plc, so that the motor shaft can "backspin"..with out damage.After 2 minutes, the motor starts again.

I've seen this happen on other back up systems, with big motors. The transition is "seamless" to computers and other machines, but with big motors they turn off and have to be reset.

Would changing the delay from genset to utility solve this?..or can it be?

At another well site, 1 well motor same size as above, along with 2 " booster pumps", are backed up via the same type of system. Same brand transfer switch, same programming on the plc.

BUT...the starters are VERY old, Clark Controllers. ( i'd say about 50 years old) And when they retransfer, none of the motors, even the 200hp motor gets bumped offline. I think the starters on the old system are not sensitive to the voltage fluctuation.

Im in the process of trying to dig up info on the soft start Westinghouse controllers, to see what can be done.



HP

 

[mpparent]

I'm assuming you have a "neutral position" delay then? ATS's? Motor operated breakers? Some more info. might be helpful.

Mike

 

[HighPotter]

Yes..it's a 400 ATS. And yes it has a delay to neutral that can be adjusted from o.1 seconds to 10 seconds.

HP

 

[mpparent]

So..no issues from utility to gen?

Mike

 

[HighPotter]

When the ats "excercises" with a full load transfer, the outcome is the same.

HP

 

[mpparent]

I wonder if you are getting an undervoltage shutdown of the motor. What kind of alarms are you seeing at the starter?

Mike

 

[RonShap]

If it is open transition and the sources are not synchronized, you will get a tremendous inrush and hopefully trip some type of protective device in the starter.

 

[HighPotter]

yes, it is showing undervoltage.

Without a closed transition system, it is impossible to synchronize the sources, correct?

HP

 

[mpparent]

HP,

As you know, if you have an open transition, there's no need to synchronize between sources. I don't believe you can correct the issue if your system is such that you have standby gen's, and you transition from utility to gen. However, you could have closed transition from gen. back to utility, although, you'd have to see if your bracing/AIC ratings are such that you can parallel both utility and gen. and provide a sync. circuit (which should be available via the ATS).

Mike

 

[RonShap]

You could check with the ATS manufacturer, because many of the controllers have the ability to delay transfer until the load is in synch with the "good" source that will be transfered to. Or just delay transfer, which disconnects the load for a predetermined period before engaging the other source.

From and ASCO manual:
INPHASE MONITOR FOR MOTOR LOAD TRANSFER
Inphase monitoring logic controls transfer and retransfer
of motor loads, so that inrush currents do not exceed
normal starting currents. It avoids nuisance tripping of
circuit breakers and mechanical damage to motor
couplings.

 

[HighPotter]

Thanks for all the support/help

So it would seem that an adjustment in the delay to neutral setting should take care of this problem.

HP