Why do they both trip???

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mbrooke said:
Correct, until the ATS transfers
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I checked for that, does not seem to be the case.

or there is a power blip from the POCO.
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In a building with literally dozens of transformers and similar breakers all over the building yet only this one is tripping?

Seems like a reach.

At that point the inrush just happens to be more than when it was manually switched on- and thus trips. Inrush magnitude is never identical.
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So this power company 'blip' you speak of are you talking 'lights out' for a second or a slow brown out or a very quick short dip?

Unless you are talking 'lights out' the transformers stay energized correct?
 
iwire said:
Again how does that, right or wrong, apply to my situation? :huh:

The transformers are energized, they stay energized for months at a time and then all of sudden it is off.

Given the fact there are no in rush loads other than the transformers themselves I am not understanding where you are heading.
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I know there are WAY better sources, but this makes mention of inrush current varying in magnitude depending on where a transformer is switched on in the voltage sine wave. The concern is great enough that some POCOs will do "point on wave switching" with large transformers which in a nut shell makes sure the circuit breaker contacts close at the exact point in the sine wave that produces low inrush.



https://www.ijsr.net/archive/v5i2/NOV161123.pdf
 
iwire said:
How?


The transformers are not cycling unless the ATS is cycling and I can find no evidence for that.
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Well at this point it looks like there is either lack of sufficient information on the system and/or a lack of sufficient knowledge among the posters to find a solution. I am definitely not a transformer weenie so I can't really help in that area and nothing else jumps out. Has there been discussion in the customer's engineering department regarding the next steps? Is anyone talking about slapping recorders on everything and waiting to see what happens the next time?
 
iwire said:
How?


The transformers are not cycling unless the ATS is cycling and I can find no evidence for that.


I checked for that, does not seem to be the case.
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So we can rule off that the ATS does not transfer load when testing/exercising the generator?



iwire said:
In a building with literally dozens of transformers and similar breakers all over the building yet only this one is tripping?

Seems like a reach.
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You are correct, reach might be a factor :D How far are those other transformers from the main gear?




So this power company 'blip' you speak of are you talking 'lights out' for a second or a slow brown out or a very quick short dip?

Unless you are talking 'lights out' the transformers stay energized correct?
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By blip a complete momentary outage when the lights go out completely for one second and then come back on. In some areas these tend to happen often.
 
iwire said:
:thumbsup:

I agree and if I learn more I will share it.

I do appreciate the help from everyone, if we could all walk the job it could be fun. :cool:
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Would your customer allow you to post a walk-through video?
 
mbrooke said:
I do not dispute that, but back then breakers tended to have a very high magnetic trip rating, assuming they even did in the first place. A good chunk of manufactures were thermal only. Over the years many arguments in the industry from fires to arc flash to magnetic force have resulted in breakers with substantially lower magnetic trip levels and even lower starting levels for those breaker which have adjustable settings.
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For at least 40 years now there has not been a major manufacturer of 'thermal only' breakers sold for general feeder and branch circuit protection.
To my knowledge the industry un-official standard for thermal magnetic breaker is roughly 5-10X for pickup with most adjustable breaker in the 2-12X range.
Yes, the actual operating and clearing speed of molded case breakers, is such that selective coordination can only be determined by physical tests.
 
jim dungar said:
For at least 40 years now there has not been a major manufacturer of 'thermal only' breakers sold for general feeder and branch circuit protection.
To my knowledge the industry un-official standard for thermal magnetic breaker is roughly 5-10X for pickup with most adjustable breaker in the 2-12X range.
Yes, the actual operating and clearing speed of molded case breakers, is such that selective coordination can only be determined by physical tests.
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Yup, you are correct :thumbsup: :) My point was going back 60+ years the mag trip levels were a lot higher, assuming they were present back then.
 
iwire said:
In a building with literally dozens of transformers and similar breakers all over the building yet only this one is tripping?

Seems like a reach.
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However, I just want to point out you might still be correct. 500 feet @ 1/0, 7.5kva, no motor loads and a 70amp breaker... now that I crunch the numbers (albeit roughly) it might be a reach.


Anyone know what the typical inrush is for dry type 480 volt transformers?
 
Okay, really dumb question here: Are the breakers tripped, or are they off?

I mean do you know that the breakers are actually tripping, and not being flipped off by someone for unknown reasons?

-Jon
 
170316-1713 EDT

This is one of those threads where there is insufficient information of the type needed to get a useful hint as to the cause. Fast response measurements need to be made that record data around the time of breaker tripping. Time correlation with what happens around the trip time is important.

iwire has said that there has been no tripping when power has been applied to the transformers. If power has been applied many times without tripping, then it is unlikely that transformer inrush is the cause of the breaker problem.

On transformer inrush current. I have previously discussed this several times. Unless you have studied magnetic circuit theory, and the characteristics of various ferromagnetic materials, then you probably have no real understanding of what happens when voltage is applied to a transformer. The shape of the magnetization curve for the core material and how far up this curve it is driven in a normal cycle, the magnetization level at the time of turn off, the resultant residual magnetization, and the point in the voltage cycle when power is reapplied determines inrush current which is mostly of 1/2 cycle duration. But it does take many cycles to reach a steady state condition. But only that first half cycle is of significance relative to typical circuit protection,

For a view of transformer inrush current see my photos P6, P7, and P8 at http://beta-a2.com/EE-photos.html .

The transformer used in my experiment probably used a core material like U.S.S. Transformer 72-29 from circa 1950. More efficient transformers today are probably more square loop in shape and would have higher peak inrush currents.

I think instrumentation of the proper capability is needed to monitor the problem iwire has.

.
 
mbrooke said:
I know there are WAY better sources, but this makes mention of inrush current varying in magnitude depending on where a transformer is switched on in the voltage sine wave. The concern is great enough that some POCOs will do "point on wave switching" with large transformers which in a nut shell makes sure the circuit breaker contacts close at the exact point in the sine wave that produces low inrush.



https://www.ijsr.net/archive/v5i2/NOV161123.pdf
Click to expand...

OMG ... :lol:
 
gadfly56 said:
Is anyone talking about slapping recorders on everything and waiting to see what happens the next time?
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Already been done, we did not catch anything.

I do not know what the boss plans next, I assume we are waiting for the customer to look over the testing reports.
 
jim dungar said:
For at least 40 years now there has not been a major manufacturer of 'thermal only' breakers sold for general feeder and branch circuit protection.
To my knowledge the industry un-official standard for thermal magnetic breaker is roughly 5-10X for pickup with most adjustable breaker in the 2-12X range.
Yes, the actual operating and clearing speed of molded case breakers, is such that selective coordination can only be determined by physical tests.
Click to expand...

FWIW the building is not more than 3 years old
 
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