Breaker tripping with ATS Transfer 2

[amesolutions]

Dear Colleagues
I have been having a problem with a breaker consistently tripping whenever I retransfer from Generator to Utility.It is a closed transition switch.

The problem is this, when ever you retransfer from generator to utility, the 200 amp 3-phase breaker will keep tripping. There is no motor loads connected to this breaker at all. It however has connected downstream around
10-15 ,415 V 15 KVA Transformers. All of which are single phase 110v secondary, powering lights, calculators. etc.NO motors at all.Could it be inrush from the Txs when I retransfer??

The problem i thought could have been motor related with inrush currents, when switching, but no motors are present. The in-phase monitor is also on, and swicthes around 8-10 degrees, but the breaker still trips. It does not trip when transferring from utility to genset however(remember the switch is between a dead source and a live one, when this occurs).

Please advise on what the problem could be and possible solutions. i have checked and the neutral and ground is bonded. The generator and utility both share the common. neutral and ground, so a switched neutral ATS
would not be necessary.

Could there be inrush of the Transformers, be a problem or not really?

> Can the problem be solved depending on the on the cause, by:
>
> An overlapping neutral switch and y?
> OR
> A delayed transition switch and y?
> OR
> any Type of surge protection on that breaker?
> OR
> Disconnection of that particular breaker prior to retransfer, via a load disconnect feature on the panel.


Any of your views will help. I have put a PQA on th esaid breker and it registered nothing prir to tripping.The breaker is a magnetis trip.Can the fast switch cause an instantaneous spike in the magnetis flux to trip the breaker?The breaker already ha sthe trip setting to max.

Thanking you all in advance

AMESOLUTIONS

 

[amesolutions]

Sorry Guys i meant it was an open transition switch not a closed one.

 

[rbulsara]

Why do you have 'in phase' monitor if this is a 'open' transition switch?

I think it is a closed trasition switch.

Regardless, you are transferring the ATS too fast. Add the delay between transfers (3 sec or so) or reduce the permissible phase angle diff to 5 degrees or less.

This is a case of trasnformer inrushes, and it becomes even worse when you are tranfering with 8-10 degree phase angel difference.

We have had similar issues with electronic transfer switches which transfers within 1/4 cycle but a phase angel difference of 10 degrees or more often causes problems.

Other alternative is to upsize the breaker (say 400A)to accomodate your 10-15 transformers. 15 kvA transforerms can have inrsuhes well in excess of 12 times the FLA.

 

[DanDel]

The 'In-phase' monitor is correct for an open-transition ATS to prevent this type of problem with motor loads; but I have seen the same problem caused by transformer loads.
There could certainly be enough transformer inrush current to caues a trip; simply calculate by multiplying the FLA of the transformers by 10 (I'm assuming they are all under 2500kVA).
Most PQAs are very good at measuring transient voltage changes in sub-cycle time intervals, but they may not measure current spikes as closely, since current is usually averaged over a certain time interval.

 

[davidbeach]

amesolutions - Is there a chance that you have a UPS (or something similar) downstream of the ATS? I've seen the same thing happen with an in-phase monitor on an ATS allowing a fast transfer at too much phase difference and the input filters of the UPS drawing a significant spike of current on transfer; enough to trip a circuit breaker between the ATS and the UPS.

 

[amesolutions]

Dear Colleagues

Thank you very much. It is an open type ATS, and yes the in phase is allowing retransfer of around 8 degrees or so. I will try and upgrade the Breaker. This should suffice. If not i will put th eload on a contacter and wire it into the load disconnect delay, from the control panel.This should shut off the load in a imely manner before the actual transfer to avoid th etransformer inrush.

Thankyou once mor eand i will keep you all posted. Oh before i forget i checked and there are no UPS loads at the moment on the breaker.

Thanx again guys

 

[TP123]

Have you adjusted the magnetic trip or pick up on the 200A CB? It may be set at minimum. You will see some value of inrush as the transformers are energized.

 

[peebee]

We had a similar problem recently. See thread237-95997 .

Looks like the time delay on the breaker was not long enough (due to the use of zone interlock breakers).

I've also had a similar problem at a different site due to transformer inrush tripping out a phase rotation relay. Strange. I suspect a longer time delay on that would have taken care of the problem -- but the ultimate solution there was to disable the phase relay.

Hope this helps.

Can you provide any more information on the type of breaker feeding the equipment, and if you have it, any information on the magnitude of the fault, trip mode (L, S, I, G, etc)? If you're using molded case breakers, your only option may be to increase the size of the breaker. . . . .

 

[amesolutions]

I will get bck to you ASAp. Thanx peebee, and the rest

 

[manager1]

If your transfer switch has a dead band timer then set it for at least 10 sec. Once loads are in excess of 50 kw you should delay transfer from source to source for at least 10sec.Of course unless loads can be synchronized before transfer. It is not advisable to increase breaker size.

regards

 

[amesolutions]

Well this is the case once more

After careful thought, i was wondering, how can it be inrush currents from the transformers that are causing the breaker to trip only from a live source to a live source(ie. generator to utility on retransfer?), if the switch is switching so fast(ASCO 7000 series switch, open transition).I thought,that a delay woud cause the transformers to de-energize, which would require energizing current when retransferred, which would trip the breaker?

The thing is this was never happening with the past switch, breaker based switch.

Can anyone explain what actually happens when the switch retransfers so fast, and the scenario that occur with the transformers that would cause the breaker to trip?

Cant I just install a 200 Amp thermal trip breaker instead?

I have to double check and see if any wiring is different from how the last switch was installed.It is a 4-wire wye system. Any thoughts on how an incorrect wiring of the new switch can cause this problem...if it can at all?

 

[rbulsara]

Yes..traferring too fast can causes much more severe inrush..I will post an article that kinda explain that (technical jargon) for power trasnformers but the theory apply to to any transformer.

Plus we have witnessed this during testing of static transfer switches which switches in less than a cycle.

The gist of the theory is the magnetics doe not get enough time to decay, and the of reclosing another source may cause more inrush.

As I said I have to find that article....dont have time right now..

 

[rbulsara]

I can't link to my computer, but it is GE document GER-3989.

You should be able to find that by search engine..

Explanation given in article 2.1 of that docuemnt for remanennt flux and the moment at which the second voltage is applied is applicable in this case...I think...

 

[davidbeach]

An other reason it might happen transfering from gen to utility and not the other way around is that the utility is likely to be a stiffer source. For a given condition, a stiffer system can provide more current. You may come close to tripping when going from utility to gen and then being just over the tripping current going the other way.