ATS won't transfer back

[living2learn]

I currnetly have a square D ATS and I am almost positive it is a 3 pole 480v. The problem lies when I kill utility power the Gens fire up and and the ATS switches and life is good, but when Utility comes back the Transfer switch won't transfer back instead the open transisition starts to transfer then it stops halfway through and I have no power to my load, so I lost the data center. I am visiting the site next week I need a good plan of attack.

Could it possibly be a ground fault located somewhere preventing the return to utility?

Circulating currents on the ground?

Square D ATS are crap (Square D service techs have nothing)

Anybody experience anything like this?

 

[alehman]

I can't think of any reason it should stop in the neutral position. I doubt it's due to any problem on your system. More likely a problem with the ATS controller, or maybe a stuck or broken auxiliary switch. Are any errors indicated?

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[waross]

The switch mechanism may be binding.
There may be a set of relay contacts that have failed.
On some types the operating pulse may be too long or maintained.
Ground faults, circulating current. Not likely. These would show up in normal operation.
There are so many types of ATSs and controllers that about the only thing I can suggest is don't waste time looking for an ephemeral ground fault and/or circulating current until you have spent a week checking everything else.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

I agree with the comments above. A ground fault would be about the last thing I would be thinking about. Sounds more like a mechanical problem in the switch or some component failure in the switch.

David Castor

http://www.cvoes.com

 

[GenSwgrEng]

I strongly doubt you've got a problem on the power-end of the ATS. It is most likely the ATS controller or operator (not you, the device that operates the contacts). If there were some sort of problem with the power, the ATS controller should not initiate a retransfer to begin with, and certainly should not stop in the neutral position.

Is this a true UL-1008 transfer switch or a pair of circuit breakers? If it is a breaker pair, check for a trip indication on the utility breaker. SqD had problems with nuisance trips on their Micrologic trip units. After a breaker opens, the trip unit could trip, preventing reclosure. Of course, if the normal breaker were tripped, you'd think the ATS controller would be smart enough to stay on generator. But like you said, SqD ATSs are crap.

Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and other people who can't handle the truth.

 

[waross]

I had one where the transformer tap on one transformer of a bank was set lower than the others. Following an outage the voltage on one phase was just a little less than needed to overcome the switching hysteresis of the ATS. Once transferred back to the grid, the switching hysteresis was enough that it would stay on the grid. WE set the tap up on the low transformer and all has been well since.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[unclebob]

The only way an ATS would stop at the neutral position when re-transfering would do so because of a timer on the neutral position. This delay is usually a matter of seconds.

 

[waross]

The only way an ATS would stop at the neutral position when re-transfering would do so because of a timer on the neutral position. This delay is usually a matter of seconds.

I can think of at least three types of transfer switch where this statement is not valid.

Bill
--------------------
"Why not the best?"
Jimmy Carter