3PH transformer blows breaker on power up

[gar]

211213-1917 EST

Ragin:

What does turns ratio have do with anything I have discussed? I could certainly measure unloaded voltage ratio in both directs, and do an average, but this has nothing to do with magnetizing current.

.

 

[Ragin Cajun]

A messed up winding job can make things much worse than normal. Just a thought. Verifying TTR was standard when we installed large transformers, the 30/40/50 MVA size. Just thought a small xfmr can benefit as well.

 

[gar]

211213-2343 EST

Ragin:

If the primary had too few turns and secondary was correct, then your suggestion is good one.

.

 

[FOG1]

update DMG Mori performed testing determined transformer was defective. They ordered a new one fro Fed Pac came in last week we swapped it our. Turned off and on 10-12 times and no blowing the breaker. Went to start it up today and guess what blowing the breaker.

 

[Flicker Index]

https://www.iosrjournals.org/iosr-jeee/Papers/Conf.17017/Volume-2/8.%2059-63.pdf?id=7590

As already addressed, the timing of deenergizing and re-energizing affects the inrush. The other factor is the available fault current at the point of connection, which is affected by the PoCo transformer, primary impedance and the total cabling distance from your transformer to PoCo transformer.

Nuisance Tripping of Fuses or Breakers at Energization

When a transformer is energized, it draws a large current for a few cycles to establish the eletromagnetic field. During this time, the transformer load has little to no effect on the initial transformer inrush. Inrush can vary depending on where the sine wave is during initial energization and...

americas.hammondpowersolutions.com

 

[FOG1]

https://www.iosrjournals.org/iosr-jeee/Papers/Conf.17017/Volume-2/8.%2059-63.pdf?id=7590

As already addressed, the timing of deenergizing and re-energizing affects the inrush. The other factor is the available fault current at the point of connection, which is affected by the PoCo transformer, primary impedance and the total cabling distance from your transformer to PoCo transformer.

Nuisance Tripping of Fuses or Breakers at Energization

When a transformer is energized, it draws a large current for a few cycles to establish the eletromagnetic field. During this time, the transformer load has little to no effect on the initial transformer inrush. Inrush can vary depending on where the sine wave is during initial energization and...

americas.hammondpowersolutions.com

Well as i stated before the other older 75 KVA transformer hooked to same power source does not do this. Also explain why when we swapped it out last week it was turned off and on 10-12 times and never tripped anything! But let it set not used for 4 days and now it blows the breaker! That makes no logical sense, the inrush current doesn't just miraculously turn off and on.

 

[synchro]

Has the new transformer been connected to the equipment? If so, are there VFDs or other loads that have rectifiers? If rectifiers are present, perhaps there's an open diode causing DC current to flow on the secondary winding which then applies a unidirectional magnetic flux through the transformer core. Because such a unidirectional flux will be unopposed by the primary winding, it will shift the excursions of the flux within the transfomer core in one direction. This could possibly make core saturation more likely and extend its duration and/or level when the transformer is turned on, resulting in more inrush problems.

 

[FOG1]

The machine tool has a disconnect on it and it is not on. So there is zero secondary load when powering the transformer on.

 

[winnie]

Well as i stated before the other older 75 KVA transformer hooked to same power source does not do this. Also explain why when we swapped it out last week it was turned off and on 10-12 times and never tripped anything! But let it set not used for 4 days and now it blows the breaker! That makes no logical sense, the inrush current doesn't just miraculously turn off and on.

Inrush is somewhat random depending upon the timing of the AC cycle at the switching event.

If you've fixed things so that now you have a 1 in 20 chance of tripping the breaker on inrush, you might see exactly what you saw.

Breakers can also age if subject to high overcurrent events. Perhaps flipping the breaker 10-12 times might have actually caused the problem? (This IMHO is a reach, and unlikely.)

Jon

 

[FOG1]

I understand the timing issue that has been suggested, but when I installed it I flogged that disconnect and never tripped the breaker in the main panel. When to fire up machine today and it did the same thing. That can’t be explained away in my opinion.

 

[FOG1]

I could of course go back to it being hooked directly to the 200amp main breaker which the other transformer would trip it when hooked up that way. My 75kva is hooked to a disconnect with 125 slow blows that’s fed by 200 amp main disconnect breaker. Never an issue it’s a older build date.

 

[gar]

See my P6 photo at

BETATRONICS&reg, Electrical photos, communication, Long Cable, High Baud Rate, RS-232, fast, I232, vendor, supplier, manufacturer, industrial

Electrical photos.

beta-a2.com

which uses an ordinary transformer core material from possibly 40 to 50 years ago.

If a newer core material was used you would likely see an even higher peak inrush current relative to rated full load current for the same transformer power rating. If the transformer is good, then you may need a means to reduce peak inrush current. For example some added impedance. You could used added input resistance, or inductive impedance. This could be left in after the transformer is turned on, or shunted out after power up.

In power supplies I made I used a negative temperature coefficient thermistor in series with an input circuit breaker to my transformer to greatly reduce peak inrush current so that a circuit breaker at the input would be very much closer to tripping on overload somewhat close to the transformer rating. I put many of these in auto plants with good results.

.

 

[ptonsparky]

Longer, smaller wires feeding it. In this case, VD is you friend.

 

[FOG1]

Well the saga continues DMG hired a local electrical contractor to come in and check everything out a month and a half ago. They basically found nothing wrong with the installation and tested the transformers and they checked out. Verified the amp draw on the primary with no load on secondary to be true. So they found a older 2005 build transformer and sent to us, we installed it yesterday turned it off and on at least 12 times never blew the breaker, came in this morning blows it every time you throw the disconnect on to power the transformer. Also check the primary side with amp-probe clamp on, 12.27-13.82-18.23 amps on each respective leg with no secondary load! That's almost double what the 2021 built units were.

 

[gar]

220326-1804 EDT

FOG1:

You do not understand magnetic circuit theory, the characteristics of ferromagnetic materials, and what and how to make measurements that will answer your question.

For the characteristics of transformers that affect inrush current, and the characteristics of breakers, you are using breakers that are rated far too close to steady state current to not expect random no load inrush current to trip your breaker.

You need to get a scope, a single phase transformer, current probe and start looking at inrush current.

.

 

[FOG1]

220326-1804 EDT

FOG1:

You do not understand magnetic circuit theory, the characteristics of ferromagnetic materials, and what and how to make measurements that will answer your question.

For the characteristics of transformers that affect inrush current, and the characteristics of breakers, you are using breakers that are rated far too close to steady state current to not expect random no load inrush current to trip your breaker.

You need to get a scope, a single phase transformer, current probe and start looking at inrush current.

.

You may have missed the previous post that we eliminated the 100 amp breaker and it blow the 200 amp main on the outside of the building. The whole time you want to tell me I don’t know why I am doing or understanding I can tell you the 75 kva doesn’t do any of this. That’s real world and it was previously justified because old transformers was built differently than new high efficiency transformers, well the one they sent is 2005 and it does the same thing as a 2021. I ask for help not to be schooled or belittled.

 

[synchro]

gar does have a good point about the value of using a current probe and scope to diagnose the issues.
In addition to inrush, it would provide insight into the nature of the excess current that you're seeing when you can get the breaker to hold. For example, if the current waveform shows unusually high peaking then that would indicate that the transformer is going into relatively strong saturation.
Voltage waveforms on a scope would also indicate the quality of the power being supplied.

 

[FOG1]

why would the power being supplied even be a question? It coming from the same service entrance it's a 400 amp 3ph service split into two 200 amp feeds. The 75kva transformer is on one feed that as I have stated a zillion times before does not have this problem. The 51 kva's all have had the same problem the old build 51 kva did same thing as the two new 2021's did. As I posted today the old build draws almost double the amperage that the new build 51kva's did! I will also state again that the 75kva draws less than 2 amps with no secondary load on it while being 33% larger. Again we eliminated the 100 amp "undersize" breaker and the 51 kva blew the 200 amp main breaker on the outside of the building. I contacted the electrician that DMG hired to come in and check everything out and he is baffled by the latest finding also. DMG sent in their tech with the fancy Fluke power analyzer and took all kinds of readings, nothing definitive from them either! They don't know, I don't know, electrician doesn't know......................................I guess i have a unicorn in Illinois!

 

[gar]

220326-2215 EDT

FOG1:

See my scope plots P6 and P7 a https://beta-a2.com/EE-photos.htm .

The steady state RMS load current for a 50 year old transformer at full load is 175 / 120 = 1.46 A or a peak current of 2.06 A. My worst case peak inrush current was 40 A. This is a 20 to 1 ratio.

A more modern transformer with a more square saturation curve probably has a greater ratio of peak inrush current, and will be more sensitive to primary voltage level compared to rated primary voltage than my old transformer

..

 

[ptonsparky]

why would the power being supplied even be a question? It coming from the same service entrance it's a 400 amp 3ph service split into two 200 amp feeds. The 75kva transformer is on one feed that as I have stated a zillion times before does not have this problem. The 51 kva's all have had the same problem the old build 51 kva did same thing as the two new 2021's did. As I posted today the old build draws almost double the amperage that the new build 51kva's did! I will also state again that the 75kva draws less than 2 amps with no secondary load on it while being 33% larger. Again we eliminated the 100 amp "undersize" breaker and the 51 kva blew the 200 amp main breaker on the outside of the building. I contacted the electrician that DMG hired to come in and check everything out and he is baffled by the latest finding also. DMG sent in their tech with the fancy Fluke power analyzer and took all kinds of readings, nothing definitive from them either! They don't know, I don't know, electrician doesn't know......................................I guess i have a unicorn in Illinois!

Did they happen to share those power analyzer readings?