mbrooke
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Faults with Transformers
- Thread starter hello21
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mbrooke
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.....
Double post
Double post
well not really
typicallly the ngr is on the main
so you don't know which branch tripped, so you lose everything
I have extensive experience with ngr systems
done all the time
far more often than ngr
ask around here: industrial electricians, which do you see more often?
ug delta or ngr for plant dist
pos usually has a neut derived
it is a function of the physical fault, Z, etc
mbrooke
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Well, these can tell you in real time since each individual circuit is monitored:
https://www.benderinc.com/products/ground-fault-monitoring-grounded/linetraxx_rcms150
Second one can place differential protection on none critical circuits. The diffy will trip for any ground fault.
On an ungrounded system the fault current may be to low, and may require directional elements as it may be "seen" by GFPs feeding none faulted circuits.
Delta is more common due to legacy. If we started today all over again it would be solid or NRG. Ungrounded is a bad idea.
True. And distance, material, ect.
However it does not change the fact ungrounded system can experience over voltages in excess of 6 to 8 times for anything other than solid fault.
https://www.google.com/url?sa=t&rct...442277941635&usg=AOvVaw2__vN0bJ1jTKjyDNkTy5xh
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this has become a circle jerk
pointless discussing a subject with one who lacks understanding and only responds to be arguementative and to get the last word
you can have it
remember, this started with your assertion the primary function of a transformer is fault attenuation
you still have neverbsaid what you do
t&d engineer
pe
electrician, residential, commercial, industrial
and I suspect you will not do so, evade and redirect
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mbrooke
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Hey- I just want us to have an intelligent discussion. Share knowledge. Thats all. I don't understand why you are so stuck on- and offended- by an old thread from 6 months ago.
jumper
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Sigh....
not stuck or offended
you are projecting
just re-realizing you can't have an intelligent discussion
it devolves into defense of absurdity
ie, xfmrs primary function is fault mitigation
I notice you evaded the question, what do you actually do
others have no issue doing that: education, experience, etc
it gives one an idea of what level to engage and how to craft the depth of the conversation
mbrooke
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I evade because I want to stick to the topic- old threads and job title is way out there- albeit I am partly responsible for veering this thread from transformers to HRG.
Yes you are right transformers are on the bottom of the list for fault current reduction, but my point was that the OP was not to far off in thinking that because he is correct in theory. All trafos have Z. Perhaps I conveyed that poorly.
kwired
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First part of this response is key:
When there is a fault on secondary the transformer doesn't say, oh a fault, it just sees it as an unusually high current load. Current on secondary rises, is limited by transformer impedance as well as conductor impedance in the faulted circuit pathway. Primary current is going to rise also - at same proportion as primary to secondary voltage ratio.
In some cases primary circuit can have enough resistance to be current limiting also, so if the primary can't draw enough then it will limit what current the secondary sees. Many of our fault current calculations we assume the primary has unlimited amount of current available, but reality is there is always limitations to it.
mivey
Senior Member
You are correct. We sometimes specify higher impedance transformers to reduce available fault current. But that is not the transformer's primary purpose.
mivey
Senior Member
Yes they are. While it may not be their primary function, that can be one of their functions. I have seen a two-stage transformation used to reduce available fault current using standard available transformers.
mivey
Senior Member
You are correct of course.
mivey
Senior Member
You could, but why not at the service so you have one transformer reducing the available fault current and making the transformation? Two birds. A reactor would be more efficient but one solution does not fit all cases.
mivey
Senior Member
Correct, and you can spec a different impedance.
Pretty common in substation design to specify an acceptable impedance range and to sometimes spec a higher impedance to reduce available fault current. Just another tool in the toolbox just like reactors are another tool in the toolbox.
mbrooke
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mivey
Senior Member
Too late to assert that. Maybe you have not done it. But it has been done in the utility world for a long time. Much longer than any of us have been around.
So there!
Too late to assert that. Maybe you have not done it. But it has been done in the utility world for a long time. Much longer than any of us have been around.
So there!
never seen a utility that wanted to burn $$$ by increasing system Z, you want to LOWER it, not RAISE it
system Z is not fault mitigation
careful selection/engineering of epd's is
why do they use <2% xfmrs?
they don't care about faults, their equipment can withstand them, and they have no liability to the customer
I worked with Tesla, been around awhile :lol:
can't spend too much time here, got 3 side projects
new gen swgr for a hi-rise sr home
develop an Act 537
EPC scada systems for 2 stp's
so you guys keep thinking that a xfmr is the best and primary means of fault attenuation :thumbsup:
don't quit your day jobs...what is brookes day job? it's a secret lol
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