mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Thats 100% rue, but I mentioned delta- wye, meaning power is "going" into the delta primary and out the wye secondary. You are thinking the opposite.
Faults with Transformers
- Thread starter hello21
- Start date
- Status
Thats 100% rue, but I mentioned delta- wye, meaning power is "going" into the delta primary and out the wye secondary. You are thinking the opposite.
glad you agree facts are 'true' lol
you misunderstand the concepts
why do you think they only show a yg;d? because it identical to a d:yg, only signs change
pretty sure I know the difference between the prim and sec
the term is power is 'delivered' to the prim, and 'supplied' to the load by the sec
doesn't matter though
the sequence components are the same
if Y sec, the fault circulates in the delta prim
has to, the fault dissipates energy/power and it has to come from somewhere, and the only somewhere is the prim
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
And, as I said, in delta wye zero sequence current will not pass through. Your basically confirming what I'm saying.
what you are saying is like saying 'a dog is not a cat' :lol:
zero seq can't exist in a delta
but fault current can, and it circulates in the delta
look at the math in the text
but we digress
xfmr's are not used for fault reduction
CLR
I limiting fuses
NGR's or NGZ's for gf's
etc
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
I don't think we even disagree- what I said was that a delta wye will not pass zero sequence current- you mistook that for wye grounded delta.
In regards to fault reduction, why wouldn't a trafo be used? Is cost what you have in mind?
BOTH will see the fault reflected
the math is the same for yg:d or d:yg
there are many better and less costly waysvto do it
research 'current limiting reactors'
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
No need to research, I've personally seen current limiting reactors (air type) put on 23kv feeders to limit current. I've also seen power plant single lines where 480:277/480 trafos were used to reduce fault current- but to be fair a lot of those had ungrounded systems and it was to get a neutral for lighting- however fault current was still in the consideration.
I agree, a trafo is perhaps the most expensive way out of a dozen, but still technically possible.
But I do get your point- and I think we can agree on this one.
the 480 d: 480 y was to derive a neut as you said
not fault limitation
if it already were y they would insert a y:y iso xfmr to reduce i fault
techically possible
not economically feasible and there are much better ways
that is why it is never done
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
I have yet to see a Y-Y 600 volt and under transformer. Sure you could custom make one (MGM does it https://www.mgmtransformer.com/ ), but an off the shelf delta wye will do. Saves on N wire as well. So even if fault current was purely a concern and the supply was wye, the trafo would still be delta wye.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
In regard to fault current reduction, a transformer provides it incidentally, at the expense of energy waste to resistive and core losses which you pay for both when the transformer is loaded and when it is unloaded.
A series reactor set, OTOH, consumes less power than the equivalent transformer when the load is on and no power at all when the load is off.
Initial cost is not the only cost factor to consider.
Sent from my XT1585 using Tapatalk
A series reactor set, OTOH, consumes less power than the equivalent transformer when the load is on and no power at all when the load is off.
Initial cost is not the only cost factor to consider.
Sent from my XT1585 using Tapatalk
that is because they don't use them
kind of defeats the purpose
the reason they use delta in plant/industrial settings are 2 fold
serves only 3 ph loads
can operate on a gf
not to save a wire
a wye-wye can be unstable under certain conditions
most have a sec tertiary delta winding
:happyyes:
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Nope, series in the example I'm thinking of. To limit fault current down to 10k amps when all the trafos are paralleled together. I know that for a fact.
Last edited:
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
You just said:
http://forums.mikeholt.com/showthread.php?t=192495&page=3&p=1928465#post1928465
If the supply was wye, the trafo wouldn't automatically be a wye primary. Almost all 600 volt dry types are delta wye or delta delta. All off the the shelf 480:480/277Y isolation are delta wye. No engineer, if seeking isolation, is going to order a none standard unit just because the 480 volt service is solidly grounded. You keep implying that if the trafo was for isolation, it would have been Y:Y and not delta wye. Not the case, nothing about isolation stops a delta wye.
I'm not talking about ungrounded systems. I'm talking about a delta primary and wye secondary trafo.
What I was referring to was this:
Delta wye isolation would require 3 wires + ground primary feed.
Wye wye isolation would require 4 wires + ground primary feed.
So you do save a wire by having a delta primary isolation transformer.
Very true, thank you, which is why that isolation was delta wye and not wye wye.
it was an absurd example to show the absudity of stating that the use of a delta-wye 480:480 is for fault reduction or for sl fault clearing...ridiculous lol
it is to derive a neut for 1 ph loads
saving 'the wire' or what we call the neut is not why they use delta in a plant
it's operational continuity
btw, delta is ungrounded in inductrial settings ( may be corner grounded but you need 'the wire')
Last edited:
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Depends on the POCO. Generally it is avoided, not found in some territories, but for some a countable amount of substations have feeder reactors.
But you are right, shunt reactors are also encountered and needed, often for underground cables to cancel out excessive capacitive current.
Most of the time thats what it was used for. However, again, if I wanted to reduce fault current nothing stops me from going to 480:480/277.
Again, not what I had in mind. I was thinking only of the feed to a D-Y vs Y-Y and nothing else.
But since we are on the subject, yes ungrounded delta is for service continuity provided you are only taking bolted ground faults into account. I say solid, because an arcing or intermittent fault will cause many more problems then if you just solidly grounded the system. Which is why high resistance grounding is used today where service continuity is required (outside of isolated power systems in health care of course).
good enginerring?
it's poor design
nrg is used for several reason
it lowers frame potential
clears ground faults
but ungrounded delta with gf protection is just as common
maybe more so
the only industry that uses ngr as a standard is mining
and by law, not by choice
it can cause issues and you must ground to sqrt3 x ph-ph v
arcing faults severity is not a function of delta or wye
- Status