26 Apr
1999
26 Apr
'99
9:33 p.m.
"Daniel T. Burrows"
<danburrows(a)mindspring.com> wrote:
> Close but not quite right. For single phase installations the power
company
supplies 2
hots and neutral. This is a center tapped secondary and the
neutral is earthed at the service entrance.
No, for split-phase, the power company does not "supply" a neutral from the
distribution system. The neutral is *only* tied to the center tap of the
secondary and to ground. It is not tied to anything on the primary side of
the transformer; that would be bad. The primary of
this transformer
is fed from only 1 high voltage phase.
I don't believe this; it doesn't match the descriptions I've read
I've always seen it shown in diagrams with the
primary connected across two
phases of the three-phase. Otherwise you need a high-current return path
somewhere else.
Take a close look at rural areas and there is only 1 High voltage line
present.
It is fed to the HT input of all the pole transformers.
To even the loading of the phases, the transformers for
split-phase service
have their primaries distributed between the three possible combinations of
the three phases.
When there are 3 phases available that sometimes is the case. Look closely
at the pole transformers and in most cases when there are 2 or more
transformers mounted on 1 pole there is only 1 HT input to each transformer.
If it were between phases there would be 2 HT inputs.
Dan
26 Apr
26 Apr
10:12 p.m.
On Mon, 26 Apr 1999, Daniel T. Burrows wrote:
Maybe where you're at, but generally not here (small town Illinois).
In the more-populated rural areas (10 or so houses per mile) all 3 phases
of the 12kV local loop are run. If the houses are all about the same age,
each pole-pig is fed off successive pairs of phases (AB, BC, CA,...).
Newer houses jumble this slightly. Rarely, in sparse areas or
clusters of houses in the middle of nowhere, a single big pole-pig
converts to about 4kV to ground. Then smaller ones make the 234V.
I've always
seen it shown in diagrams with the primary connected across two
phases of the three-phase. Otherwise you need a high-current return path
somewhere else.
Take a close look at rural areas and there is only 1 High voltage line
present.
It is fed to the HT input of all the pole transformers. When there are 3 phases available that sometimes is
the case. Look closely
at the pole transformers and in most cases when there are 2 or more
transformers mounted on 1 pole there is only 1 HT input to each transformer.
If it were between phases there would be 2 HT inputs.
??? Every place that I've seen that has 2 or 3 12kV-to-234V transformers
has them between pairs of phases.
Richard
rws(a)enteract.com
11:48 p.m.
----- Original Message -----
From: rws <rws(a)enteract.com>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Sent: Tuesday, 27 April 1999 12:42
Subject: Re: Powerlines
> Take a close look at rural areas and there is
only 1 High voltage line
> present.
> It is fed to the HT input of all the pole transformers.
Same thing is done in rural areas in Oz. They are called SWR lines, which
is TLA for Single Wire Run AFAIK.
Not sure of the voltage, but I think it's around 8kv. (240v to subscribers)
They are somewhat unpopular, and are prone to surges and sags etc.
Given the nature of the return path, (ground) and the way it would be
affected by weather etc, this is not surprising.
'Normal' mains is delivered to subscribers elsewhere as a single (or two or
three - if they can justify it) active, neutral, ground.
IIRC, you are allowed a max of 80A per 240v phase. Need is based on
Lighting circuits being 8 amp, 1 single standard outlet @ 10A and a HD
outlet (for A/C's and the like) @15A. Stoves, Hot water and the like are
hardwired to their own circuit and fuse/breaker. Some large homes may need
2 phases, especially now as some of the SAA wiring regulations cut
drastically the number of outlets allowed on a single circuit. (Doesn't
affect existing installations of course) It's moderately difficult (not to
mention expensive) to get a proper 3 phase (415v) outlet installed, ETSA
(Electricity Trust of South Australia) simply won't do it unless you can
demonstrate you have a real need for it.
Cheers
Geoff Roberts
VK5KDR
Computer Systems Manager
Saint Mark's College
Port Pirie, South Australia.
Email: geoffrob(a)stmarks.pp.catholic.edu.au
netcafe(a)pirie.mtx.net.au
ICQ #: 1970476
10:44 p.m.
On Mon, 26 Apr 1999, Daniel T. Burrows wrote:
That is what I was trying to decsribe above.
elsewhere.
Which, of course, is not to suggest that other pole routings may well
carry a different HT phase to achieve that balance.
- don
"Daniel T. Burrows"
<danburrows(a)mindspring.com> wrote:
> Close but not quite right. For single phase installations the power
company
supplies
2 hots and neutral. This is a center tapped secondary and the
neutral is earthed at the service entrance.
No, for split-phase, the power company does not "supply" a neutral from the
distribution system. The neutral is *only* tied to the center tap of the
secondary and to ground. It is not tied to anything on the primary side of
the transformer; that would be bad. The
primary of this transformer
is fed from only 1 high voltage phase.
I don't believe this; it doesn't match the descriptions I've read I've always seen it shown in diagrams with the
primary connected across two
phases of the three-phase. Otherwise you need a high-current return path
somewhere else.
Take a close look at rural areas and there is only 1 High voltage line
present.
It is fed to the HT input of all the pole transformers.
To even the loading of the phases, the
transformers for split-phase service
have their primaries distributed between the three possible combinations of
the three phases.
When there are 3 phases available that sometimes is the case. Look closely
at the pole transformers and in most cases when there are 2 or more
transformers mounted on 1 pole there is only 1 HT input to each transformer.
If it were between phases there would be 2 HT inputs.
Dan 
27 Apr
27 Apr
12:52 p.m.
"Daniel T. Burrows" <danburrows(a)mindspring.com> wrote:
Take a close look at rural areas and there is only 1
High voltage line
present.
It is fed to the HT input of all the pole transformers.
[...]
When there are 3 phases available that sometimes is
the case. Look closely
at the pole transformers and in most cases when there are 2 or more
transformers mounted on 1 pole there is only 1 HT input to each transformer.
If it were between phases there would be 2 HT inputs.
How can the transformer possibly work if the primary is only connected to one
HT line? What is the other side of the primary connected to? Where's the
return path?
9378
days inactive
9379
days old
4 comments
5 participants
participants (5)
-
danburrows＠mindspring.com -
donm＠cts.com -
eric＠brouhaha.com -
geoffrob＠stmarks.pp.catholic.edu.au -
rws＠enteract.com