|
Science Forum Index » Electronics - Misc Forum » Transformer
Page 1 of 1
|
| Author |
Message |
| SparkyGuy |
 Posted: Sat Feb 03, 2007 5:05 am |
|
|
|
Guest
|
480 (delta) -to- 208 (wye) transformer being used for step-up purpose (rather
than step-down).
Is it mandatory to use neutral in the wye hook-up?
Grounding is provided by same-size conductors as the phase cables.
No flames, please. It's a sincere question.
Thanks,
Sparky |
|
|
| Back to top |
|
| Bud-- |
| Posted: Sat Feb 03, 2007 1:58 pm |
|
|
|
Guest
|
SparkyGuy wrote:
Quote: 480 (delta) -to- 208 (wye) transformer being used for step-up purpose (rather
than step-down).
Is it mandatory to use neutral in the wye hook-up?
Grounding is provided by same-size conductors as the phase cables.
No flames, please. It's a sincere question.
Thanks,
Sparky
If there are 3 transformers connected wye the neutral is required or
else the neutral point will float and the voltage across the 3
transformers will be different depending on the secondary load.
(If there are 2 transformers - Scott or T connection - I don't think you
need the neutral.)
The secondary system will be ungrounded?
--
bud-- |
|
|
| Back to top |
|
| SparkyGuy |
| Posted: Sat Feb 03, 2007 1:58 pm |
|
|
|
Guest
|
Bud sez:
Quote: If there are 3 transformers connected wye the neutral is required or
else the neutral point will float and the voltage across the 3
transformers will be different depending on the secondary load.
(If there are 2 transformers - Scott or T connection - I don't think you
need the neutral.)
It's a single 3-phase transformer labeled for use as 480 (delta) -to- 208
(wye) step-down. Which, reading your statement above, means that phase
voltages will be different in the primary and secondary depending on loading.
Yes?
Quote: The secondary system will be ungrounded?
Common ground between supply and load, at the transformer chassis.
Sparky |
|
|
| Back to top |
|
| Robert Baer |
| Posted: Sun Feb 04, 2007 12:57 am |
|
|
|
Guest
|
SparkyGuy wrote:
Quote: 480 (delta) -to- 208 (wye) transformer being used for step-up purpose (rather
than step-down).
Is it mandatory to use neutral in the wye hook-up?
Grounding is provided by same-size conductors as the phase cables.
No flames, please. It's a sincere question.
Thanks,
Sparky
Grounding of the neutral is preferred for safety, and it prevents
non-symmetrical loading of one phase from shifting the voltage and phase
of the others. |
|
|
| Back to top |
|
| Michael Moroney |
| Posted: Sun Feb 04, 2007 5:46 pm |
|
|
|
Guest
|
SparkyGuy wrote:
Quote: 480 (delta) -to- 208 (wye) transformer being used for step-up purpose (rather
than step-down).
Is it mandatory to use neutral in the wye hook-up?
Be aware that doing this results in a wye-delta transformer configuration.
This has a problem that if you lose a phase, the transformer will try to
power the lost phase from the other two. Therefore, expect the breaker to
pop whenever you lose a phase, when it attempts to backfeed the local
grid.
On the other hand, if you don't connect the wye common point to the
neutral, it won't do this. Even if the load on the delta side is
unbalanced, the configuration won't try to generate any neutral current,
it happens to work out. You'll still have single phasing, of course.
But before you do this, run it by someone with more knowledge of these
things than myself, as well as whether code allows this. I do know
that a local electric company does this when powering an old segment of
delta-connected distribution system from a higher voltage wye system.
The common connection of the primarys don't connect to the neutral. |
|
|
| Back to top |
|
| Guest |
| Posted: Mon Feb 05, 2007 12:04 am |
|
|
|
|
On Feb 3, 9:05?am, SparkyGuy <Sparky...@mumcrank.ck> wrote:
Quote: 480 (delta) -to- 208 (wye) transformer being used for step-up purpose (rather
than step-down).
Is it mandatory to use neutral in the wye hook-up?
Grounding is provided by same-size conductors as the phase cables.
No flames, please. It's a sincere question.
Thanks,
Sparky
If your output winding is the delta one, then you have nowhere to
attach a ground except one of the phases which probaly not what you
want. You only need a neutral at the star point when you use a wye/wye
transformer. |
|
|
| Back to top |
|
| Donald Kinney |
| Posted: Mon Feb 05, 2007 12:24 am |
|
|
|
Guest
|
Quote: 480 (delta) -to- 208 (wye) transformer being used for step-up purpose
(rather
than step-down).
Is it mandatory to use neutral in the wye hook-up?
Grounding is provided by same-size conductors as the phase cables.
No flames, please. It's a sincere question.
Sparky
Neutral on the wye is mandatory.
There is no neutral on the delta side.
Each delta phase is feed from two of the hots.
Instead of having three power circuits like AN, BN, CN, you get AB, BC, CA.
If you tie any delta phase to ground you will be chasing voltages on the
grounds.
Donald |
|
|
| Back to top |
|
| Bud-- |
| Posted: Mon Feb 05, 2007 4:38 am |
|
|
|
Guest
|
SparkyGuy wrote:
Quote: Bud sez:
If there are 3 transformers connected wye the neutral is required or
else the neutral point will float and the voltage across the 3
transformers will be different depending on the secondary load.
(If there are 2 transformers - Scott or T connection - I don't think you
need the neutral.)
It's a single 3-phase transformer labeled for use as 480 (delta) -to- 208
(wye) step-down. Which, reading your statement above, means that phase
voltages will be different in the primary and secondary depending on loading.
Yes?
If the transformer has 3 sets of coils I'm going to change my answer. I
think the connection on the delta side would force the voltages on the
wye side to be substantially equal. I think the voltages on the delta
side would be a little closer to equal with a connected neutral and
losses would be lower since the delta side is not forcing a balance on
the wye side. Anyone with a better theory?
Particularly some small 3 phase transformer units are made with 2 sets
of coils with a Scott/T connection which could be connected without a
neutral.
Quote:
The secondary system will be ungrounded?
Common ground between supply and load, at the transformer chassis.
The transformer 480V delta side would be ungrounded unless you "corner"
ground one of the phases.
--
bud-- |
|
|
| Back to top |
|
| Rich Grise |
| Posted: Tue Feb 06, 2007 1:13 pm |
|
|
|
Guest
|
On Sat, 03 Feb 2007 09:58:45 -0800, SparkyGuy wrote:
Quote: Bud sez:
If there are 3 transformers connected wye the neutral is required or
else the neutral point will float and the voltage across the 3
transformers will be different depending on the secondary load.
(If there are 2 transformers - Scott or T connection - I don't think you
need the neutral.)
It's a single 3-phase transformer labeled for use as 480 (delta) -to- 208
(wye) step-down. Which, reading your statement above, means that phase
voltages will be different in the primary and secondary depending on loading.
Yes?
This is the opposite of what you said in your original post. You said 480
wye to 208 delta. Now, you're saying 480 delta to 208 wye. Which of these
it is makes a lot of difference.
Whichever side ends up with the Wye connection needs the neutral
throughout, and it will probably be grounded at the entrance panel
(If it's the input side) or a "common neutral" if it's on the equipment
side. Delta has no neutral; both need the safety (Earth, Frame) ground in
any case.
Hope This Helps!
Rich |
|
|
| Back to top |
|
| joseph2k |
| Posted: Fri Feb 09, 2007 12:33 am |
|
|
|
Guest
|
SparkyGuy wrote:
Quote: 480 (delta) -to- 208 (wye) transformer being used for step-up purpose
(rather than step-down).
Is it mandatory to use neutral in the wye hook-up?
Not always, local regulations vary. It is, however, customary and typical.
It has advantages as other responders have noted.
Quote: Grounding is provided by same-size conductors as the phase cables.
That is fine, always works OK and is always legal if all leads are of
sufficient size.
Quote:
No flames, please. It's a sincere question.
Thanks,
Sparky
--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.
--Schiller |
|
|
| Back to top |
|
| Tony Williams |
| Posted: Sun Feb 11, 2007 12:50 am |
|
|
|
Guest
|
In article <63c85$45c6e7ee$4213eacf$5372@DIALUPUSA.NET>,
Bud-- <remove.BudNews@isp.com> wrote:
Quote: If the transformer has 3 sets of coils I'm going to change my
answer. I think the connection on the delta side would force the
voltages on the wye side to be substantially equal. I think the
voltages on the delta side would be a little closer to equal
with a connected neutral and losses would be lower since the
delta side is not forcing a balance on the wye side. Anyone with
a better theory?
I think that is correct. Any 3-phase transformer
with a delta on one side (pri or sec) has the benefit
that the delta winding internally circulates third
harmonic currents and balances the wye-side so that
the neutral is reasonably stable. This means that
the star point may or may not be earthed and, (if it
is), does not require a heavy gauge connection. It
also means that a wye-connected secondary allows a
4-wire supply that can have simultaneous balanced and
unbalanced loads without much penalty.
Contrast that with a wye-wye transformer, where the
neutrals can be very unstable, requiring heavy gauge
neutral wiring.
In the UK the delta-wye is the standard 11KV 3-wire
to 240V (line-neutral) 4-wire configuration for
domestic and industrial distribution.
--
Tony Williams. |
|
|
| Back to top |
|
| |
