Why do they both trip???

[K8MHZ]

20-30% very steady, no real load changes.

These panels only supply emergency lighting, exit signs, things like fire panels and other items the AHJ requires to be on an emergency panel.

There are other panels and ATSs for other optional generator loads.

Later I will post some more details, just not into it right now.

:thumbsup:

Maybe it's time to just drink beer and watch AC/DC videos. As an experienced troubleshooter, I recommend it. Especially with Smart TV, YouTube and surround sound. We have come a long way since the day when I would just drink beer and listen to AC/DC records on a stereo.

 

[Electricalartist]

As someone mentioned, the vibration of a fault can trip sensitive breakers, also might want to check the available air/aic

 

[steve66]

I probably wouldn't hesitate to turn those magnetic settings up a little, maybe even halfway. Although a coordination study would really be the way to go.

Also, I'd still like to know what size transformers are on those breakers. I'd usually use at least a 125 amp for a 75KVA xformer.

 

[George Stolz]

I didn't see Page 3 until just now. I read up on the Spectra RMS, the dial is definitely instaneous current settings, and the values of the six points are listed on the rating plugs of the breakers. The stated purpose is "to deal with inrush of motors and transformers", which prompted me to thinking more about whether these breakers were right for the transformers to begin with.

I'm with Steve, take a long hard look at the connected transformers, apply 450 to start with, make sure the basics were put together right (to code maximums), and then spend a few minutes with Mike's short circuit calculator and see how the numbers on the rating plugs compare. I find myself having to learn transformers over again each time I have to figure out a new piece of one line, so it stands to reason that someone might have used a rule of thumb for the primary side of these that doesn't stand out like a sore thumb, but isn't taking advantage of the full allowances of the NEC. I wouldn't turn down any selective coordination cheerfully offered, but I have yet to see a guy on the side of the road with a sign that says, "will coordinate OCPDs for food."

Seems like just last week I was banging a load on-off-on-off and whatever it was refused to trip, and then some automatic process did that and it tripped reliably. This electricity stuff is damned illogical at times.

http://apps.geindustrial.com/publib...Technical|GET-7002|PDF&filename=GET-7002D.pdf

http://m.ecmweb.com/nec/small-dry-type-transformers-and-appropriate-ocpd-sizing

 

[GoldDigger]

Just a thought:
When you turn a load switch off and on you are hitting a random point in the current waveform.
But if the automatic on involves the closing of a contactor, it is possible that the contact closure is at least partially synchronized to the voltage waveform applied to the coil
So if it happens to hit the worst case time (zero crossing of voltage) once it is likely to always hit that worst case timing.

mobile

 

[iwire]

I probably wouldn't hesitate to turn those magnetic settings up a little, maybe even halfway. Although a coordination study would really be the way to go.

To me if I do what you suggest the customer could just as well hire a 'master of all trades' from Craig's list. I am not going to change a thing without direction.

I didn't see Page 3 until just now. I read up on the Spectra RMS, the dial is definitely instaneous current settings, and the values of the six points are listed on the rating plugs of the breakers. The stated purpose is "to deal with inrush of motors and transformers", which prompted me to thinking more about whether these breakers were right for the transformers to begin with.

You too George?

Repeat after me, there are no motors, there are no motors, there are no motors.

The breakers have never (AFAIK) tripped when first energizing the transformers. The breakers handle the inrush of transformers just fine.

I'm with Steve, take a long hard look at the connected transformers, apply 450 to start with, make sure the basics were put together right (to code maximums), and then spend a few minutes with Mike's short circuit calculator and see how the numbers on the rating plugs compare. I find myself having to learn transformers over again each time I have to figure out a new piece of one line, so it stands to reason that someone might have used a rule of thumb for the primary side of these that doesn't stand out like a sore thumb, but isn't taking advantage of the full allowances of the NEC.

To what end am I doing this? The transformers do not trip at start up which is why 450 is set up to allow larger OCPDs.

I wouldn't turn down any selective coordination cheerfully offered, but I have yet to see a guy on the side of the road with a sign that says, "will coordinate OCPDs for food."

This customer is worth millions if not billions and they have in house engineers so we are not looking for a hand out.

The mag settings are being noted in the report and will be brought to the attention of the customer. It will be their call what to do from there.

 

[iwire]

OK, more details. One thing I need to clear up right away is about the wire size, I looked at the wires over a year ago and my memory was telling me 500s in 4" .... when I looked again last Monday night it was 1/0s in 2". You wonder how I was so off? Well in this building there are 4" with 500 and 600s everywhere. So with that out of the way here are details

Below is panel PPGM, it has the 200 amp main breaker that has tripped. The breaker at the top above the ATS has not tripped.

The feeder to transformer TGEM is 70 amps and has tripped.

The line coming out of the left of PPGEM is the 100 amp feeder heading to the remote building that has also been tripping.

And the panel directories for those panels.

Now the remote building

 

[George Stolz]

This customer is worth millions if not billions and they have in house engineers so we are not looking for a hand out.

In which case you've found the one in a million job where we can all leave it in their hands.

Edit: running late with a 1/4 cup of coffee in me, but isn't TGEM's 70A breaker supposed to be a 125A?

 

[jim dungar]

...but isn't TGEM's 70A breaker supposed to be a 125A?

The NEC does not contain 'minimum' sizing of protective devices for transformers.
In the old days, before plug-on 125A panel style branch breakers and energy effcient transformers, it was not uncommon to see 70A breakers used. Also, 80A and larger breakers cost more back then.

 

[winnie]

GoldDigger has an interesting thought in post 85; the breakers handle transformer inrush _most_ of the time, so when the panel is manually switched on the breakers hold.

But some automatic switching event happens at just the right moment in a cycle, or synchronized just wrong with a moments before shutdown, so that there is greater inrush and the breaker trips.

TGAREM says 7.5kVA but fed by a 100A breaker. Should that be 75kVA?

Depending on the actual size of TGAREM, George Stolz's question may apply to both feeders; are the breaker trip ratings high enough to handle transformer inrush in all conditions or simply most.

-Jon

 

[jim dungar]

,,,are the breaker trip ratings high enough to handle transformer inrush in all conditions or simply most.

We will never know.

Nobody does actual 'inrush' testing of small transformers. Everything is done theoretically. I have seen inrush tables complied assuming the transformer is an air core inductance, because the math is easier.
Transformers are magnetic devices so hysteresis also comes into play. Where in the waveform when it was turned off, versus where it turns on can be a problem.

 

[iwire]

GoldDigger has an interesting thought in post 85; the breakers handle transformer inrush _most_ of the time, so when the panel is manually switched on the breakers hold.

But some automatic switching event happens at just the right moment in a cycle, or synchronized just wrong with a moments before shutdown, so that there is greater inrush and the breaker trips.

What switching event? One on the 208/120 side of the transformers? Did you look at the panel directories? There are no heavy loads being switched.:huh:

Steve brought up something in post 22 I am looking into.

Maybe when they test the generator, and when the transfer happens, if the timing is just right there is enough inrush on both feeders to cause both breakers to trip, and one also has enough to trip the main.

Hmm, hmy: this exact issue has happened in the past and I was able to fix it by programing in a transition delay into the transfer switch.

TGAREM says 7.5kVA but fed by a 100A breaker. Should that be 75kVA?

The panel main is 100, the transformer primary breaker is 20 and has not tripped.

 

[mbrooke]

OK, more details. One thing I need to clear up right away is about the wire size, I looked at the wires over a year ago and my memory was telling me 500s in 4" .... when I looked again last Monday night it was 1/0s in 2". You wonder how I was so off? Well in this building there are 4" with 500 and 600s everywhere. So with that out of the way here are details

Below is panel PPGM, it has the 200 amp main breaker that has tripped. The breaker at the top above the ATS has not tripped.

The feeder to transformer TGEM is 70 amps and has tripped.

The line coming out of the left of PPGEM is the 100 amp feeder heading to the remote building that has also been tripping.

And the panel directories for those panels.

Now the remote building

e
Thanks My money is on transformer inrush as mentioned. I take all the EM lights are LED or electronic florscent? (just checking)

 

[mbrooke]

The breakers have never (AFAIK) tripped when first energizing the transformers. The breakers handle the inrush of transformers just fine.

I am willing to argue that. :thumbsup: Transformer inrush varies based on the residual magnetism of the core and at the exact instant the sign wave was switched off and then on.

 

[mbrooke]

The NEC does not contain 'minimum' sizing of protective devices for transformers.
In the old days, before plug-on 125A panel style branch breakers and energy effcient transformers, it was not uncommon to see 70A breakers used. Also, 80A and larger breakers cost more back then.

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.

 

[gadfly56]

I am willing to argue that. :thumbsup: Transformer inrush varies based on the residual magnetism of the core and at the exact instant the sign wave was switched off and then on.

What, from 1/2 second to 20 minutes?? If it doesn't go "click, pop" it's not gonna go on "residual magnetism" later on.

 

[iwire]

I am willing to argue that. :thumbsup: Transformer inrush varies based on the residual magnetism of the core and at the exact instant the sign wave was switched off and then on.

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.

 

[mbrooke]

What, from 1/2 second to 20 minutes?? If it doesn't go "click, pop" it's not gonna go on "residual magnetism" later on.

Varies in magnitude for the first few cycles- not duration. This has been proven over and over on large transformers (ie over 5MVA) however the physics remain the same for all sizes.

 

[mbrooke]

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.

Correct, until the ATS transfers or there is a power blip from the POCO. 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.

 

[iwire]

My money is on transformer inrush as mentioned.

How?


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