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Breaker sometimes trips on transformer inrush current
7

Breaker sometimes trips on transformer inrush current

Breaker sometimes trips on transformer inrush current

(OP)
I have a technical question. I'm hoping you can help me out.
 
At the local convention center they have seventy-five 300 kva GE K Factor transformers for temporary show power.

Each transformer is protected by a GE 500 amp SGLA36AT0600 current limiting circuit breaker.
 
These transformers have no loads for days at a time and the convention center would like to turn the transformers off during downtime.
 
(They are unloaded during switching and installed in an air conditioned tunnel).
 
This could save about $500 a day on the power bill.
 
I have reports of the breakers sometimes tripping when the transformers are re-energized. (I assume this is inrush current at a bad time in the cycle.)
I can find no problems with the transformers.
 
My Question:
 
Will re-energizing the tripped breaker two or three times in a row damage the breaker or damage the transformer?
 
Is it ok to use this breaker to turn this unloaded transformer on/off a few times a week?
 
Thanks,
 
Andy

RE: Breaker sometimes trips on transformer inrush current

Hi Andy.
For my pinion, no problem (for both Q's).
Problem only, why CB triped?
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

Tripping under high current conditions isn't doing the breakers any good.  It would be much better to adjust the instantaneous trips or otherwise fix the root problem which is that the breakers are too small and/or the settings are too low.  Repeated tripping under high current will definitely shorten the expected life of the breakers.  

RE: Breaker sometimes trips on transformer inrush current

If my memory is still good, I read recently in the IEEE Blue Book that MCCBs should be replaced after two trips under full tripping current. Granted this may be difficult to determine, but it does support dpc's comment. Thanks again dpc!  

RE: Breaker sometimes trips on transformer inrush current

With the small size of the transformers, there probally hasen't been much study of inrush completed. But it very well could be inrush. Question: Has there been tripping at other times? Like maybe other inrush events?

You also did not state the type of protection, but I would expect time and inst. over current. It is possible that they could not be set properly for inrush.

Your other question about closing and tripping breakers several times, there is a wear and tear factor anytime you open and close breakers, no matter what type of breakers. So to operate them more will require more maintenance or replacments as time goes.

My thoughts are you should see what is behind the difficulties to close issue, and the $500 a day seems significent, so investigate the cost of maintenance, and make a compairson. In any event, operating the breakers like that will require more maintenance, and eventual replacments, so the maintenance group needs to be up to the task.

RE: Breaker sometimes trips on transformer inrush current

Thanks Folks.
I learned something about MCCB and IEEE requerements.
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

It's almost certainly transformer inrush.  On a 500 A breaker, it should be possible to increase the instantaneous pickup enough to stop this from happening.  

RE: Breaker sometimes trips on transformer inrush current

Andy32821;  You understand what's happening correct?

 The transformers can get disconnected while on, say, the peak negative of the cycle.  This leaves the core magnetized in that state.  Then later someone closes the breaker while the negative part of the cycle is in effect.  Now the flux continues to build and the transformer promptly saturates.  Current skyrockets 12X is not uncommon.  Breaker trips.

 If you can monitor or control when you turn OFF the breakers so the transformer shuts down unmagnetized this wouldn't be an issue.

Anyone heard of a device for this?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Breaker sometimes trips on transformer inrush current

Keith,

It's done with large high voltage breakers in some situations, but it requires single-pole switching.  I've never seen it done for an application like this.  

For this voltage and breaker type, the practical solution is to size the breaker's instantaneous trip to ride through the maximum inrush.  These types of problems are errors in design or in establishing proper breaker settings.  

RE: Breaker sometimes trips on transformer inrush current

Thanks for the enlightenment dpc.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Breaker sometimes trips on transformer inrush current

Actually, you can't shut the transformer off at zero voltage, even using single pole tripping because you can only interrupt on a current zero and without out unity power factor you never have voltage zeros and current zeros at the same time.  What you can do with single pole switching, generally at 500kV and sometimes at 230kV, is you can close back in where you want on the voltage wave, pole-by-pole, and minimize the inrush current.  It is an interesting concept and totally non-applicable for the application of the OP.

The transformer voltages aren't stated, but assuming 480V, I'd have sized the breaker at 800A, with an instantaneous setting of 8000A, that 500A is rather small.  I'd expect peak inrush currents between 4300A and 5400A and that 500A breaker won't let 5400A through without tripping.

RE: Breaker sometimes trips on transformer inrush current

Magnetisation inrush current is maximum when the switching is done at zero point of the sinusoidal voltage wave, with residual flux remaining in core from previous switching off .This is because the flux is lagging voltage by 90 degrees.In EHV breakers this inrush can be reduced by switching the breaker exactly when the voltage is at the peak.This is called controlled switching of breakers.This power electronic device is prohibitively costly and limited for  use with EHV breakers.Theoretically it can be used with any breaker.
 Transformer in rush current always contain 10-60 % second harmonic component depending on the angle of voltage at which switching is done.In differential relays, harmonic restraint feature is provided( ie relay will not respond when there is second harmonics in the over current )to avoid maltripping during energisation.I dont think  overcurrent relays can incorporate that feature.For such small breakers the only solution seems to go for time delay with higher  instantaneous ratings as David mentioned.

RE: Breaker sometimes trips on transformer inrush current

That breaker has adjustable (digital) instantaneous over current (IOC) trip settings. The NEC allows you to set them for upwards of 13X the load FLC if you demonstrate that the breaker is nuisance tripping on inrush of inductive loads. I'd say you have demonstrated that. Crank up the IOC setting and quit exercising those breakers; they aren't that fat.

RE: Breaker sometimes trips on transformer inrush current

Hi PRC.
I heard about this device ( I think made by Sweden).
Could you please send any link.
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

ABB is supplying such device.Please go to abb.com and type controlled switching under search -you will get all information.

RE: Breaker sometimes trips on transformer inrush current

Thanks PRC.
I found.
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

(OP)
Hi Guys,

This breaker is a GE sprctra RMS electronic breaker but does not have the digital readout. Only an inst pot that is at max.

My main concern is damaging the breaker with resets. Since this is an electronic breaker I am hoping that resets are not a problem.

I assume that cycling the breaker 50 time a year to turn the transformer off when not in use will have little impact on the breaker's life. But I get myself in trouble assuming things.

As far as the tripping goes, I can change the 500 amp plug to a 600 amp plug if this will help. The transformers have primary and secondary protection. It's probably not cost effective to add any other hardware.

I will do more studies on whats causing the trips but I need to come up with a procedure on what happens when a breaker does trip. (A rare event).

The whole idea is to save money and at $500 a day a $3000 breaker is not a big deal. (However a $20,000 transformer might get the maintenance manager irked).



I am thinking of this procedure for the switching technician:

If the breaker trips when turning the transformer on then open the secondary breaker and try the primary breaker again.

If the primary breaker trips again wait 5 minutes and try once more.

If the breaker trips again leave it off and call an electrician.

Is this asking too much of the breaker or is this in the normal design duty of this style breaker?

Thanks for any help you can offer.

Andy

RE: Breaker sometimes trips on transformer inrush current

Switching the breaker on should not be a problem. The issue is that the breaker is probably interrupting 5000 amps or more when it trips on instantaneous. That is hard on the breaker.
Try the 600  amp trips on one or two breakers. Knowing that there are inrush problems, I would try two or three resets before calling the electrician, however you are on site and it is ultimately your call as to how many times to retry.
The inrush is a fact of life and cannot be reasonably avoided. The breaker tripping is detrimental to the breaker and should not be happening. Step one is checking the settings. Step two is changing the rating plug. Step three is changeing the breaker. All transformers have inrush current. Transformer breakers should withstand the inrush without tripping.
Switching with no load on the transformer is probably a good idea.
respectfully

RE: Breaker sometimes trips on transformer inrush current

The problem is the wear and depletion of the contacts - the trip unit type is not an issue and does not make a difference to the longevity of the breaker.

If the 500 A trips are at max instantaneous, you will need to look at larger breakers - since it is a 600 A frame, they can probably be changed out to 600 A, but only if the feeder ampacity is adequate.  

Frequent tripping of a 500 A breaker on xfmr inrush would not be an acceptable situation for me.  



RE: Breaker sometimes trips on transformer inrush current

Changing the rating plug will give you an additional 1000A of instantaneous trip range, so that may do it. The problem with changing the rating plug however may be the conductor size, but you appear to be someone who would have thought of that.

I hadn't looked closely at the specs on that breaker before, but now I see that the 500A rating plug only allows adjustment up to 5000A; 10X the rating. A 300kVA transformer is probably around 361A FLC at 480V (you never said) so if the inrush is 13X, then the 5000A setting should have sufficed. But those "K-Factor" transformers may have different magnetic characteristics that end up pushing the worst-case inrush over the edge of that 5000A limit.

RE: Breaker sometimes trips on transformer inrush current

Andi32821,
You did not specifically state wether or not the transformers are loaded when they are re-energized.  This has been assumed by many of the posts above, but it is my experience that at conventions, lighting shows, etc..., these units are randomly loaded, and they are assigned to any number of exhibitors whom will set up their shows at various times in multiple stages.  It is definitely possible that some of these have pre-wired displays or facilities which will be energized in one step, but I doubt that a large percentage would be.  Also, when taking down the shows, it is common for the exhibitors to tear down prior to de-energizing the breakers.

Am I off base in describing how your facility operates?  I have not seen these temporary power feeds used very often to energize or de-energize a fully loaded convention floor.  The "down-time" you discribed in your OP I am issuming is between shows. Or are you talking about switching these off every night during a show's run?

In any case the previous posters have provided very good insights as to what may be causing the tripping if in fact the breakers are switching on a maximally loaded transformer.

RE: Breaker sometimes trips on transformer inrush current

EEJaime I suspect that they would be shut down whenever there are multi day gaps between shows.  When no one is tearing down or setting up.  Hence the 50 times a year.

So I suspect that these transformers are rarely loaded up when they get turned on because they would be turned as any setup commences.

I thought that the inrush was greatly exacerbated by a specific loading.  Like unloaded is  a bigger problems than loaded.  Can someone enlighten me?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Breaker sometimes trips on transformer inrush current

We had a discussion on this one or two years back. I was assuming that the switch-on time was the only parameter causing the problem with high in-rush current.A German guy told me that remanent magnetism also was important. I did some measurements and realized that he was right. I then tried a simple degaussing method (adding a capacitor to the transformer secondary so that the damped oscillation carried flux down to zero) and then was able to demonstrate that my former very high in-rush current was non-existant.

If your transformers are single-phase, it could be an easy answer to the problem. Add a suitable capacitor - probably in the 10 - 100 uF region if the transformers are 300 kVA and see if that helps. Try it out on one transformer before ordering for all of them  smile

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Breaker sometimes trips on transformer inrush current

Found it! Have a look at http://www.eng-tips.com/viewthread.cfm?qid=144465&page=1

There are recordings showing inrush without and with the degaussing capacitor.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Breaker sometimes trips on transformer inrush current

"Is it ok to use this breaker to turn this unloaded transformer on/off a few times a week?"

I think he made it clear there was no load.

I never heard that unloaded may be worse. Load adds to the total. The 12X FLA rule includes (cold) load, so that you may be able to get away with 11X if energization is always done without load. Since always is tough to guarantee, stick with 12X or more.

RE: Breaker sometimes trips on transformer inrush current

Load will in general have less impact on inrush than the exact phase angle when the transformer is closed into.  What load will do, though, is to provide damping to reduce the inrush sooner.  An unloaded transformer will ring far longer than a loaded transformer, but if the transformers at issue are tripping on instantaneous then load probably doesn't matter, and with out load you do avoid any through current adding to the inrush current.

RE: Breaker sometimes trips on transformer inrush current

OP says this is a current limiting breaker. Regarding current limiting fuses, Cooper says to consider 25X at 0.01s in addition to the 12X at 0.1s due to their speed. This breaker must also be very fast to limit the current.

RE: Breaker sometimes trips on transformer inrush current

Good point, stevenal.  I'd missed that; I'm surprised they only trip occasionally.  Time to replace the breakers with non-current limiting as this is not a good application for current limiting circuit breakers (or current limiting fuses for that matter).

RE: Breaker sometimes trips on transformer inrush current

Hello davidbeach.
I understand that the breaker ratings are
Current limit x 25
Instantaneous x 10
I understand that the breaker is going out on instantaneous.
If it goes on current limit, then it may be necessary to replace internal fuses.
If the breaker uses a rating plug, it is probably a 600 amp breaker with a 500 amp plug.
The rating plugs I am familiar with are changed from the front without dismounting the breaker. Similar to changing an E-Prom.
See http://www.geindustrial.com/cwc/Dispatcher?REQUEST=PRODUCTS&pnlid=3&famid=8&catid=9993&id=cb-pd-et

RE: Breaker sometimes trips on transformer inrush current

A star Gunnar, and a thank you for this and all the other tips I have learned from you on the forum.
Thanks
Bill

RE: Breaker sometimes trips on transformer inrush current

I believe these are non-fused current-limiting circuit breakers.  At these current levels, I doubt there is much current limiting going on.  

600 A trip would be about right for a 300 kVA 480 V primary.  500 A is just too small.  The extra 100 A of trip rating would provide another 1000 A of instantaneous setting range.   

RE: Breaker sometimes trips on transformer inrush current

Hello All.
I miss something in this thread.
Pleas don't LOL on me, MCCB isn't my field.
SGLA36AT0600 type, I assume 600 is mean 600A, OP state is 500A,why?
Second, why we decide that was inst. trip, Andy wrote only about some trip not about kind of trip.
Next, I assume that this CB have some regulation of inst. trip setting, may be now it's on low level position.
I remember KM NZTM series, it was range from 2 up to 10 In. ( or something like to this)
I don't understand where installed this CB, on primary side or on secondary side, what is voltages on primary/secondary side?
What is type of load connected to this trafo?
Sounds me, that Andy open only secondary side.
For my curios only, 500$ per day saving on non loaded transformer 300kVA. non loaded transformer have only losses.
How, 1%, 5%, 10% ( it depend)?
What is a price of 1kW- half $, one $?
20.8$ saving per hour.
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

Sorry, or it's 20.8$/75 trafos.

RE: Breaker sometimes trips on transformer inrush current

Let me summarise the issues with magnetising in-rush current in transformers considering the  above discussions and also the thread pointed out by Skosgurra:


1) Transformer will be switched off when current wave  is at zero,including excitation current.So depending on Pf of load, voltage also will be near to that point in the wave with flux wave at near to maximum level.This flux ( 70-90 % of normal flux) will remain in core for several weeks till withering  down completely.When such residual flux is there in core and if the transformer is switched at the voltage wave zero level,flux has to be at the peak level.So flux  start build up over the residual flux.So this will be maximum( also excitation current) when switched at zero voltage at start of positive cycle( earlier switched  off at positive cycle) or at zero of start of negative cycle( if  earlier switched off at negative cycle).Inrush current ( 12-15 x FL current in case  of small trfs and 6-10 times  FLC in large units)magnifies from normal excitation current by 140-1000 times depending on  the size of transformer  for the same  worst conditions of switching off and ON.So inrush current as times of FLC depends on the size of transformer too.


 2) This high  inrush current is generated to drive the excess flux ( as core no longer can  contain it  due to saturation)  through the air core inductance of the winding.
So inrush current will be higher if transformer is energised from the winding nearer to core ie LV winding


 3)  Inrush current is not affected by  the grade of  silicon steel used in core.Saturation flux density is almost same for all grades of cold rolled silicon steels.
Similarly it is not affected by the flux density adopted in the core.

 4) Inrush current will be increased if energised on secondary loaded condition.Increase will be to the extent of load.

 5)  In three phase transformers,it also depends on the connection of windings.In a YY connection, inrush will be 60 % of  value during Dy connection.

 6) Before the advent of controlled switching,the only way with EHV breakers to control inrush current  was to use a closing resistor in the breaker.This was bypassed after voltage build up.

 7) One recent problem found with large transformers is the inabilty of differential relays to stop from operating during energisation.As I said in my earlier posting,restraint in relays is incorporated by sensing the second harmoinic content in inrush current.In modern large units,this is some times less tahn 10 % compared to 15-50 % in earlier days.
 

RE: Breaker sometimes trips on transformer inrush current

I agree with slava on the CB sizing, it's too small for the trafo size and 600A could solve that!
prc, I have experienced the same unwanted CB trips long ago on my previous employment on a 1MVA SST. Diff prot actuates on energization and we tried "de-sensitizing" but still diff prot picks up sometimes! Like davidbeach said, I loaded up the trafo before energizing, no more trips!

RE: Breaker sometimes trips on transformer inrush current

Quote (slavaq):

SGLA36AT0600 type, I assume 600 is mean 600A, OP state is 500A,why?
The 600 in the part number means it is a 600A frame. The frame needs a rating plug to make it work which can be anything from 250A to 600A. So in the original post, he stated it was a 500A breaker, which would mean it had a 500A rating plug installed in it. In these GE breakers, the rating plug sets both the long time thermal trip (which is the 500A rating in this case) plus it also provides the setting range for the instantaneous magnetic trip. The range is essentially 3x to 10x the rating plug value. For example, on the 500A rating plug, the instantaneous magnetic trip range is 1525 to 5060A. He later mentioned that it was set to maximum, which means 5060A, but it was still tripping. That then means that (assuming a transformer FLC rating of 361A) his inrush current is occasionally in excess of 14x FLC which is unusual, but apparently possible according to the info provided by prc above.
He can change the rating plug to a 600A unit so that the the adjustment range will increase to be 1830 to 6075A, so if set to maximum it will allow up to almost 17x FLC. However, it will come with the 600A long time trip setting, which is what the cable ratings are based on. So he can only do this if his cables are rated for 600A.

RE: Breaker sometimes trips on transformer inrush current

Quote (prc):

magnifies from normal excitation current by 140-1000 times depending on  the size of transformer  for the same  worst conditions of switching off and ON

Is this correct? Not sure I'm following this..

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Breaker sometimes trips on transformer inrush current

itsmoked, Iam sorry .I made a mistake.Thank you for pointing out.

In modern transformers normal excitation current is 3-0.5 % FLC  for distribution transformers and 0.05-0.5 % for Power Transformers(say 400-20 MVA) So inrush  enhancement for DT will be 5-30 times only ( assuming 15xFLC as inrush)and for PT 200-100 times (assuming 10x FLC as inrush)

RE: Breaker sometimes trips on transformer inrush current

O.K.
Andy may be need change plug to 600A of course if his cable are rated for 600A. Same DPC was recommended.
PRC is right, for small trafos recommended calculate inrush 16xFLA ( for example for the HI protection).
But actaully same Q's are important: where installed those CB's and what are rating voltages of trafos.
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

It is probably better, from a physics point of view, to relate the inrush current to excitation current. As prc does.

But it is not very practical when it comes to selecting trip levels or fuses. For such purposes, the inrush current related to nominal (rated) current is more common and also more practical.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Breaker sometimes trips on transformer inrush current

(OP)

Thanks for the help everyone.

Sounds like if I prevent the trips the breakers should be ok.

I will try the 600 amp plugs where needed.

If I can capture a trip on a pqm I will post the results.

Thanks again,

Andy

RE: Breaker sometimes trips on transformer inrush current

Andy,

You can change from 500 A to 600 A rating plug only if the conductor is adequately sized for a 600 A breaker.  

RE: Breaker sometimes trips on transformer inrush current

slavag
Remember that these transformer tunnels are air conditioned. I assumed that $500 per day included the energy to remove the losses as well as the transformer losses.
respectfully

RE: Breaker sometimes trips on transformer inrush current

Where are the breakers in question located?  The assumption seems to be that they are at the source of the circuit, in which case the concerns about conductor sizing would apply.  If the breaker is mounted on the transformer as a local disconnect/protection and the cables are adequately protected by something at the source end of the conductors, you can go as high as you want while still complying with the transformer protection requirements of the code.  If the source breaker meets those requirements, the local breaker could be most anything.  If these are at the transformer, my guess is that someone specified the current limiting as an attempt to provide coordination with the upstream device, but in doing so introduced a bit of over tripping.

RE: Breaker sometimes trips on transformer inrush current

Exactly, Bill, exactly.
What I think about. That problem isn't transformer inrush, problem is load on transformers( for examples restart of AIR cond., chillrers, etc..). From time to time we have same problems on the MV side, solution is reconnection load
step by step.
Regards.
Slava

RE: Breaker sometimes trips on transformer inrush current

(OP)
Hi Guys


When the new building is empty the floor box transformers use about 264 kw of power to keep the transformers energized.

So (24 hours) cost is 264 kw * 24 hour * .08 dollars/kwh = $506 a day.
The kva is almost seven times the kw so this amount includes the cable copper loss as well as the transformer heat loss.

Figure 150 days the transformers could be off and the savings would be about $76,000/year.

Since 100% of this power is turned to heat another $15,000/year could be saved on HVAC. (This is probably a low number but the convention center purchases chilled water at a very good rate so I am just guessing on the HVAC)

The two parallel cable sets between the primary breaker and the transformer primary are 250 mcm XHHW so a 600 amp breaker should be ok. (Dry air conditioned tunnel). The longest run is about 100 feet so voltage drop is not an issue.

I should have mentioned before these are 480 to 208/120 three phase transformers GE cat # 9T23B3479G13. They feed only floor pockets for exhibitor equipment (no permanent loads are connected) and are only switched off and on when the building is empty and there is zero load on the transformers.

Please let me know if it looks like I have gone astray on my number crunching.

Andy

RE: Breaker sometimes trips on transformer inrush current

Your 264 kW of losses works out to 3.5 kW per transformer.  This seems a bit high for core loss only on a 300 kVA unit, but I assume you have the core loss data.  

The 2 x 250 kcmil (copper, I assume) is good for 510 A, so you just sneak in to a 600 A breaker.  The 90 deg C ampacity in the NEC Table 310.16 generally can't be used because the breaker is rated for use only with 75 deg cable.

I'd suggest changing out one or two breakers to see if the 600 A trip is going to work.  You should pick one of the transformer that has been known to trip on inrush.  You'll have to try it multiple times to account for voltage phase angle at closing.

RE: Breaker sometimes trips on transformer inrush current

DPC,

My source Electrical Distribution System Protection third edition, pages 90 to 93. The example shows the choice of a current limiting fuse with a melt curve well above the 25X FLA at .01s. The point is that current limiting can occur due to inrush if one does not choose the right protection.

It is not clear from the the literature how the breaker in question limits current. If by speed of operation, it would look like an instantaneous trip.

RE: Breaker sometimes trips on transformer inrush current

By definition, any interrupting device considered "current-limiting" by UL must CLEAR a fault prior to the first peak current.  This will be within 1/2 cycle.  The only way a fuse can be current-limiting is by melting.

A current-limiting breaker utilizes the inherent inductance and arc resistance in the breaker mechanism and its "blow apart" contacts to achieve current-limiting status.  All molded case breakers are somewhat current limiting, but this is generally neglected in fault calculations.  The breaker must clear the fault on its instantaneous trip to be considered current-limiting.  Modern MCCBs have contacts that actually open before the breaker mechanism trips for high values of fault current.   

So the current limiting effect does depend on the size of the fuse or breaker.

RE: Breaker sometimes trips on transformer inrush current

ok will make it short

1-the problem with a breaker triping time to time, is one days it will trip for real and the operator will get it face blown or blow something...so it is better to solve the tripping probleme

2-i have seen i similar probleme were i customer had large tranformer but with low load,(money was not a issue so he went big to be secure) so inrush was quite high

3-it is a patch, but maybe you could had 1,2 switch along the circuit, to start less transformer

4-i'm not 100% sure but if you need higher inst setting
you can get an higher plug, and lower the overload setting
(if it's an electronic unit)

RE: Breaker sometimes trips on transformer inrush current

Hi folks,

That's is my first time in this forum. I am a Transmission Electrical Engineer.
Have you heard about "transformer sympathetic interaction"? This phenomenon occurs when a transformer is energized nearby others transformers, prolonging the inrush current.
In general, it happens in electric systems with very high resistances.
In the Andy's case, the inrush current may be takes a long time to decay, with the protection (I think it is overcurrent)triping properly.

To solve the questions, I suggest firt recording the currents in the transformer being enegized and, also, in the transformer already in operation to see if the phenomenon I said happens.

Regards.

H. Bronzeado

RE: Breaker sometimes trips on transformer inrush current

Welcome to Eng-tips bronzeado.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Breaker sometimes trips on transformer inrush current

Thanks, Keith!

H. Bronzeado

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