# Thread: Faults with Transformers

1. Originally Posted by Ingenieur
starting on 174 http://www.zmuda.ece.ufl.edu/Fall_20...Components.pdf
good explanation

page 193 shows yg:d

a ground fault on the y will cause a current to circulate in the delta, in essence, that is the 'ground fault current'
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.

2. Senior Member
Join Date
Jan 2016
Location
Earth
Posts
6,049
Mentioned
0 Post(s)
Tagged
0 Thread(s)
Originally Posted by mbrooke
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

3. Originally Posted by Ingenieur
glad you agree facts are 'true' lol
you misunderstand the concepts
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
And, as I said, in delta wye zero sequence current will not pass through. Your basically confirming what I'm saying.

4. Senior Member
Join Date
Jan 2016
Location
Earth
Posts
6,049
Mentioned
0 Post(s)
Tagged
0 Thread(s)
Originally Posted by mbrooke
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'
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

5. Originally Posted by Ingenieur
what you are saying is like saying 'a dog is not a cat'
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

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?

6. Senior Member
Join Date
Jan 2016
Location
Earth
Posts
6,049
Mentioned
0 Post(s)
Tagged
0 Thread(s)
Originally Posted by mbrooke
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'

7. Originally Posted by Ingenieur
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'
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.

8. Senior Member
Join Date
Jan 2016
Location
Earth
Posts
6,049
Mentioned
0 Post(s)
Tagged
0 Thread(s)
Originally Posted by mbrooke
...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

9. Originally Posted by Ingenieur
if it already were y they would insert a y:y iso xfmr to reduce i fault

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.

10. Senior Member
Join Date
Jan 2016
Location
Earth
Posts
6,049
Mentioned
0 Post(s)
Tagged
0 Thread(s)
Originally Posted by mbrooke
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.
those reactors are shunt, not series
different function

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•