"AlexW" wrote in message
...
Rob Morley wrote:
In article ,
says...

snip

My original response was to Bob Eager's point blank "no it doesn't" which
is not specific at all as to why it "doesn't". I inadvertantly accused Bob
Mannix snipping here and lack of clarity ... apologies, I mis-read the
sender in the thread.

Ah full circle. Apology accepted ). My comment about the trap was because
I guessed Bob Eager put what he did (out of devilment) to see how long
people argued about the reversing direction bit before realising it was the
50 that was wrong (which, if I may say, you weren't clear about
realising/accepting, hence my other comments). Of course it may not have
been like that at all, only he can say.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

I dont want to be pedantic but AC current is just swapping the positive
and negative electrodes around 50 or 100 times a second,

so positive and negative are switched around by AC current,

http://www.tpub.com/neets/book2/1.htm

AC AND DC

Alternating current is current which constantly changes in amplitude,
and which reverses direction at regular intervals. You learned
previously that direct current flows only in one direction, and that
the amplitude of current is determined by the number of electrons
flowing past a point in a circuit in one second. If, for example, a
coulomb of electrons moves past a point in a wire in one second and all
of the electrons are moving in the same direction, the amplitude of
direct current in the wire is one ampere. Similarly, if half a coulomb
of electrons moves in one direction past a point in the wire in half a
second, then reverses direction and moves past the same point in the
opposite direction during the next half-second, a total of one coulomb
of electrons passes the point in one second. The amplitude of the
alternating current is one ampere. The preceding comparison of dc and
ac as illustrated. Notice that one white arrow plus one striped arrow
comprise one coulomb.

blackboab wrote:
The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

can i get electrocuted by holding the NEUTRAL ?

a circuit only needs two wires to be complete.

so how does the third wire - ground - fit in the circuit ?

See http://amasci.com/amateur/whygnd.html

MBQ

great article. the current goes from live to neutral and back again 50
times a second as explained here

@@@@@@@@@@@@@@@@@@@@@@'

But still, every once in a while a Customer will get a really nasty
shock
from a cheap plastic appliance that's wet. Or perhaps an electric hair
dryer will fall into the bathtub, but the short-circuit current in the
water won't be enough to blow the fuses in the house, and the bathtub
water will become lethal. In theory there is a way to prevent this.
These Customer shocks are happening because the customers' bodies offer
a
path for current between the appliance and the lightning-safety earth
grounds. During the shocking event, some of the flowing charge is
going
in (and out) of the "hot" wire, but it is NOT going back into (and out
of)
the "neutral" wire as it's supposed to. Instead, it's going through
the
human, and also going into the grounded pipes of the plumbing.

If we could measure the current that's taking the "wrong" path, maybe
we
could detect the problem and turn off the power before anyone dies. We
can't measure the current in the plumbing, but we can measure it in the
"hot" wire, measure the current in the "neutral" wire, then subtract
them. This tells us what level of current was escaping via the
"illegal"
path through the human to ground. The subtraction should normally give
a
zero result, since there never should be a current path to ground that
isn't using the neutral wire. If we amplify the subtraction's result
and
use it to trip a circuit breaker, we'll have a new type of appliance
which
turns itself off immediately when a human gets into the electrical
path.
These devices are now required in wet areas of homes (bathrooms.)
They're
called Ground Fault Interrupters. And so we've finally entered modern
times, the "Age of the Electric Outlet with the Little Red Button Which
Pops Out!"

On Wed, 5 Oct 2005 15:37:09 UTC, "Bob Mannix"
wrote:

"AlexW" wrote in message
...

My original response was to Bob Eager's point blank "no it doesn't" which
is not specific at all as to why it "doesn't". I inadvertantly accused Bob
Mannix snipping here and lack of clarity ... apologies, I mis-read the
sender in the thread.

Ah full circle. Apology accepted ). My comment about the trap was because
I guessed Bob Eager put what he did (out of devilment) to see how long
people argued about the reversing direction bit before realising it was the
50 that was wrong (which, if I may say, you weren't clear about
realising/accepting, hence my other comments). Of course it may not have
been like that at all, only he can say.

You're absolutely right! Although I'm surprised that Alex didn't just
put his hand up and admit he was wrong...!

I snipped because I wasn't answering the other part...

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

On 5 Oct 2005 09:16:56 -0700, "blackboab"
scrawled:

These devices are now required in wet areas of homes (bathrooms.)
They're
called Ground Fault Interrupters. And so we've finally entered modern
times, the "Age of the Electric Outlet with the Little Red Button Which
Pops Out!"

Er, this is uk.d-i-y, note the UK bit.
--
Stuart @ SJW Electrical

Please Reply to group

Bob Mannix wrote:

Well I would make the assumption (for my own safety) that given a 240V
supply might generate stray neutral voltages of up to 30V

Higher voltages are not unknown on isolated overhead LV supplies in the
sticks (cue "Wanderer").

a 330kv one *might* generate neutral voltages of up to 30kv. Of
course it might not, as such supplies would be three phase and
arranged differently, but I wouldn't take the chance myself!

An HV supply won't usually have a distributed neutral conductor (just
3-phase, 3-wire). There'll be a neutral point at the transformer or
generator, earthed via a known impedance, but only the 3 phase
conductors head off outwards.

--
Andy

i know.

but most of the information is still relevant.

say what you want about the yanks being imperialist , war-mongering
*******s but their technical knowledge is pretty impressive, at least
they make good websites,

Bob Eager wrote:
On Wed, 5 Oct 2005 15:37:09 UTC, "Bob Mannix"
wrote:


"AlexW" wrote in message
.. .


My original response was to Bob Eager's point blank "no it doesn't" which
is not specific at all as to why it "doesn't". I inadvertantly accused Bob
Mannix snipping here and lack of clarity ... apologies, I mis-read the
sender in the thread.

Ah full circle. Apology accepted ). My comment about the trap was because
I guessed Bob Eager put what he did (out of devilment) to see how long
people argued about the reversing direction bit before realising it was the
50 that was wrong (which, if I may say, you weren't clear about
realising/accepting, hence my other comments). Of course it may not have
been like that at all, only he can say.


You're absolutely right! Although I'm surprised that Alex didn't just
put his hand up and admit he was wrong...!


Oh you would say that ;-)

Why be surprised?

To be honest shortly after sending my first reply the sinusoid entered
my head and I realised exactly 50 changes = 25 Hz but did not consider
it was a trick question ... and my attention was elsewhere for a while
.... After Bob M's post and decided if trick questions were the name of
the game then actually I was not wrong in the strictest sense. Rob was
right about wriggling ... but hey why not if you've been set up.

I snipped because I wasn't answering the other part...

AlexW wrote:

I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.

Alex.

That's an approximation.

If the frequency is high enough, and/or the distance is long enough, a
lot of the power gets carried as an electromagentic wave around the
conductor.

I'm used to seeing this at MHz and GHz ranges in short conductors, but
I'm pretty sure this is why HT pylons have 4 wires with airgaps for each
conductor.

Andy

Bob Mannix wrote:
"AlexW" wrote in message
...

Bob Mannix wrote:

"AlexW" wrote in message
. ..


Bob Eager wrote:


On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:




AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.


You fell into his little trap! It changes direction 100 times per second,
having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times.


So that would be 100, not 50


AC current could actually change at any frequency.


Well so it could but it *could* also be a 330,000 V AC supply, in which case
I wouldn't touch the neutral!

If the conditions were right, I'd touch the Phase. Since 33kV is
probably going to be 3 phase, I'd say any one of them...

"Bob Mannix" wrote:


Well so it could but it *could* also be a 330,000 V AC supply, in which case
I wouldn't touch the neutral!

Not in the UK it couldn't (330kV that is)


--

On Wed, 05 Oct 2005 20:41:54 +0000, Andy Champ wrote:

I'm pretty sure this is why HT pylons have 4 wires with airgaps for each
conductor.

They always seem to have cables in multiples of 3 whenever I look. One
group for each phase.

--
Gooooooood Morning Cyberspace

In article ,
John Laird writes:
On Wed, 05 Oct 2005 20:41:54 +0000, Andy Champ wrote:

I'm pretty sure this is why HT pylons have 4 wires with airgaps for each
conductor.

They always seem to have cables in multiples of 3 whenever I look. One
group for each phase.

275,000V is a bundle of two, and
400,000V is a bundle of four.
This is to reduce the electric field strength which in
turn reduces the corona discharge.

Or maybe you are referring to the 3 or 6 lines carried,
which will be for one or two 3-phase circuits?

--
Andrew Gabriel

Simon wrote:

Everyone seems to be saying tripping out the lights is a bad Idea as you may
fall over in the dark, so why not have two RCDs, one for lights and one for
everything else. I must admit ours is old and protects everything. I have

Nothing wrong with multiple RCDs. If you are on a TT install then that
is the way to go anyway. The ultimate solution you could argue would be
a RCBO for each circuit that needs one.

The argument against RCDs, is the problems of unwanted trips as a result
of "normal" leakage (some types of appliance are prone to it because
they have mineral insulated heating elements, or capacitive filters on
their mains inputs). For circuits that present very little real risk of
electrocution the negatives may outweigh the positives.

never found it turning the lights off a problem. I have only ever tripped it
by accidentally touching the neutral, I never had the nerve to touch the
live to see if it hurt. I have always liked the idea that everything in the
house was protected so that I have to do something very foolish before I can
electrocute myself. Just wish that there was one light in the garage that
came on so that I could climb across all the junk in the garage to reset it.

Why not add a non maintained emergency light then? About £20 from TLC.
Wire it to a feed on the lighting circuit in there. That will keep it
charged. When the power goes off it lights up.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

blackboab wrote:

but most of the information is still relevant.

Apart from the bit about having sockets allowed in bathrooms...

say what you want about the yanks being imperialist , war-mongering
*******s but their technical knowledge is pretty impressive, at least
they make good websites,

Alas their electrical installations are of state of the ark in
comparison to ours. So of very limited use as a source of reference
material.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

really ? how do they manage to do things like the space shuttle ?
then again two of those crashed and they lost 2 space probes they sent
to Mars. Perhaps they arent as great as they like to think.

what is the worst thing about their electrical systems ?

On 5 Oct 2005 23:24:42 -0700, blackboab wrote:

really ? how do they manage to do things like the space shuttle ?
then again two of those crashed and they lost 2 space probes they sent
to Mars. Perhaps they arent as great as they like to think.

what is the worst thing about their electrical systems ?

Err, how about twisted joints?


--
the dot wanderer at tesco dot net

"Matt" wrote in message
...
"Bob Mannix" wrote:


Well so it could but it *could* also be a 330,000 V AC supply, in which
case
I wouldn't touch the neutral!

Not in the UK it couldn't (330kV that is)


OK, OK everyone! I accept that such systems are 3-phase without a neutral
return. I thought 330kv was one of the standards (it clearly isn't). I was
making a general point about the context of the original question
determining the supply details - of course I realised almost immediately
there would be nationalgridophiles who would descend on me )..

Actually it struck me there is an interesting psychological point - the
overhead supplies in our street are 240V 3phase with neutral (every house is
connected to the neutral and they are spread across the phases). While I am
happy to touch the neutral in the house, I would be less happy to touch the
neutral on the pole, but they are connected together so that's illogical but
there you go.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Andrew Gabriel wrote:

275,000V is a bundle of two, and
400,000V is a bundle of four.
This is to reduce the electric field strength which in
turn reduces the corona discharge.

There are two other benefits to bundling:

- it significantly reduces the inductance (and hence the voltage drop),

- it improves cooling of the conductors. At full winter load those 400
kV lines are carrying about 3,000 amps per bundle, so they do tend to
get a bit warm.

--
Andy

care to elaborate ?

you arent talking about their use of torture at Abu Ghraib and
Guantanamo are you ?

blackboab wrote:

really ? how do they manage to do things like the space shuttle ?

Don't see the connection to domestic electrics... hardly rocket science
is it? ;-)

then again two of those crashed and they lost 2 space probes they sent
to Mars. Perhaps they arent as great as they like to think.

Even monkeys fall out of trees...

what is the worst thing about their electrical systems ?

Hard to choose one really... we had a long thread on this a while back.

In general they seem to have a lower level of "respect" for the
electrical systems in houses - possibly due to lower perceived risk from
the 110V supply they mostly use. However the lower supply voltage (hence
higher current and heating effect) combined with the permitted use of
poor wire jointing technique (twist on "wire nuts") and extensive use of
aliminuim cable seems to result in far more electrical fire risks.

AAUI the quality of their switch gear and accessories is lower (paper
used as insulators etc). They often don't have RCDs. Their circuit
breakers often lack the "magnetic" response facility that is standard on
ours, and ensure that high overcurrents are cleared very quickly.

They are also pretty poor on earthing systems (like not even having one
on some socket circuits!), and equipotential bonding. The lower voltage
and poorer MCBs makes earth fault loop impedances far more critical, and
it can be very difficult or impossible to achieve rapid disconnect times.

Try this thread for mo

http://groups.google.com/group/uk.d-...1e8279a6609a36
http://tinyurl.com/7h7kr

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

(Andrew Gabriel) wrote:

In article ,
John Laird writes:
On Wed, 05 Oct 2005 20:41:54 +0000, Andy Champ wrote:

I'm pretty sure this is why HT pylons have 4 wires with airgaps for each
conductor.

They always seem to have cables in multiples of 3 whenever I look. One
group for each phase.

275,000V is a bundle of two, and
400,000V is a bundle of four.

Not exclusively. 2 conductor per phase 400kV started being used in
the UK in the mid 90's and is now being used for a lot of restringing
and for all new routes.


--

On 6 Oct 2005 02:46:30 -0700, blackboab wrote:

care to elaborate ?

you arent talking about their use of torture at Abu Ghraib and
Guantanamo are you ?

Twisted joints, held together by some sort of ceramic or plastic thimble.


--
the dot wanderer at tesco dot net

On 05 Oct 2005 23:59:05 GMT, (Andrew Gabriel)
wrote:

In article ,
John Laird writes:
On Wed, 05 Oct 2005 20:41:54 +0000, Andy Champ wrote:

I'm pretty sure this is why HT pylons have 4 wires with airgaps for each
conductor.

They always seem to have cables in multiples of 3 whenever I look. One
group for each phase.

275,000V is a bundle of two, and
400,000V is a bundle of four.
This is to reduce the electric field strength which in
turn reduces the corona discharge.

Or maybe you are referring to the 3 or 6 lines carried,
which will be for one or two 3-phase circuits?

I think I am. How is the field strength diminished by having multiple
conductors in close proximity ? (My AC knowledge is very sketchy.) It's
voltage-determined, is it not ? I'd assumed multiple conductors were used
simply as a compromise between current, heat generated, weight, and ease of
construction.

--
(singing): Spam! Lovely spam! Lovely spam!

"blackboab" wrote in message
oups.com...
really ? how do they manage to do things like the space shuttle ?
then again two of those crashed and they lost 2 space probes they sent
to Mars. Perhaps they arent as great as they like to think.

what is the worst thing about their electrical systems ?


It isn't long since this topic became a long running argument in the
newsgroup. Lets not go down that road AGAIN.

On Thu, 6 Oct 2005 12:42:08 +0100,it is alleged that The Wanderer
spake thusly in uk.d-i-y:

On 6 Oct 2005 02:46:30 -0700, blackboab wrote:

care to elaborate ?

you arent talking about their use of torture at Abu Ghraib and
Guantanamo are you ?

Twisted joints, held together by some sort of ceramic or plastic thimble.

Sprung steel coil actually, and they burn up significantly less often
than strip connector.

--
There is no reason anyone would want a computer in their home.
- Ken Olson, President of DEC, 1977

On Thu, 6 Oct 2005 17:57:00 UTC, Chip wrote:

On Thu, 6 Oct 2005 12:42:08 +0100,it is alleged that The Wanderer
spake thusly in uk.d-i-y:

On 6 Oct 2005 02:46:30 -0700, blackboab wrote:

care to elaborate ?

you arent talking about their use of torture at Abu Ghraib and
Guantanamo are you ?

Twisted joints, held together by some sort of ceramic or plastic thimble.

Sprung steel coil actually, and they burn up significantly less often
than strip connector.

I've also seen plain ceramic thimbles with nothing else in
them....Scruits they used to be called.

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

On 6 Oct 2005 18:27:19 GMT,it is alleged that "Bob Eager"
spake thusly in uk.d-i-y:

On Thu, 6 Oct 2005 17:57:00 UTC, Chip wrote:

On Thu, 6 Oct 2005 12:42:08 +0100,it is alleged that The Wanderer
spake thusly in uk.d-i-y:

On 6 Oct 2005 02:46:30 -0700, blackboab wrote:

care to elaborate ?

you arent talking about their use of torture at Abu Ghraib and
Guantanamo are you ?

Twisted joints, held together by some sort of ceramic or plastic thimble.

Sprung steel coil actually, and they burn up significantly less often
than strip connector.

I've also seen plain ceramic thimbles with nothing else in
them....Scruits they used to be called.


Yes, nasty things they were too. US Lighting manufacturers still
produce a plastic equivalent that isn't UL Listed for anything at all
(not that the dang things actually fit the wires either).

Admittedly the old versions without the steel spring were a little
'pointless'. The modern ones are the result of years of development,
and counterintuitively provide a very good joint with copper-copper.

With alumin(i)um wiring, all bets are off, most US electricians suck
air in through their teeth and start mentally making out a replacement
bill when they find it.

--
There is no reason anyone would want a computer in their home.
- Ken Olson, President of DEC, 1977

In article .com,
blackboab wrote:
The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

It's actually 100 times a second. The 50 Hz refers to a full cycle - from
zero to + then zero to - and back to zero. Relative to *both* conductors.

can i get electrocuted by holding the NEUTRAL ?

What causes harm is potential difference. You could have a million volt
supply, and if one side is earthed you should be able to touch that
conductor safely. But not the other one...;-)

a circuit only needs two wires to be complete.

so how does the third wire - ground - fit in the circuit ?

In an ideal world both neutral and earth are at the same potential.

--
*A fool and his money can throw one hell of a party.

Dave Plowman London SW
To e-mail, change noise into sound.

John Laird wrote:

How is the field strength diminished by having multiple conductors in
close proximity ? (My AC knowledge is very sketchy.) It's
voltage-determined, is it not ?

This is basic electrostatics and is the same at DC. Field strength is
potential gradient. The field close to the surface of a round wire
carrying a given charge per unit length is inversely proportional to the
radius of the wire. Thus field concentration and the risk of breakdown
always occurs near sharp edges or points. A rough engineering
approximation for more complicated structures is to think of the field
as proportional to one over the radius of curvature of a structure
component. That's why much of the metalwork of high voltage equipment
has smooth rounded edges.

You can visualise it in terms of field lines (lines of flux) being more
crowded together near a feature of small radius. High electric flux
density implies high field strength since the two are proportional to
each other, the constant of proportionality being called permittivity.

--
Andy

"Andy Wade" wrote in message
...
John Laird wrote:

How is the field strength diminished by having multiple conductors in
close proximity ? (My AC knowledge is very sketchy.) It's
voltage-determined, is it not ?

This is basic electrostatics and is the same at DC. Field strength is
potential gradient. The field close to the surface of a round wire
carrying a given charge per unit length is inversely proportional to the
radius of the wire. Thus field concentration and the risk of breakdown
always occurs near sharp edges or points. A rough engineering
approximation for more complicated structures is to think of the field as
proportional to one over the radius of curvature of a structure component.
That's why much of the metalwork of high voltage equipment has smooth
rounded edges.

You can visualise it in terms of field lines (lines of flux) being more
crowded together near a feature of small radius. High electric flux
density implies high field strength since the two are proportional to each
other, the constant of proportionality being called permittivity.


Its years since I studied this aspect but from memory the bundle of
conductors "looks like" a single larger conductor with an effectively larger
diameter and thus a reduction in stress/corona is achieved. Someone else
might be able to recall better from less aged studies? The 4 conductor
bundles associated with 400kV are relatively easy to visualise this but 275
kX with 2 conductors must "look like" an oval I suppose.
As a matter of interest I had a tour round Drax power station about thirty
years ago and the primary connections between the station and the grid
switching breaker farm were run in single heavy bars for a short distance.
The noise of frying air molecules was astounding.

On Fri, 7 Oct 2005 08:06:43 +0000 (UTC), "John"
wrote:

"Andy Wade" wrote in message
...
John Laird wrote:

How is the field strength diminished by having multiple conductors in
close proximity ? (My AC knowledge is very sketchy.) It's
voltage-determined, is it not ?

This is basic electrostatics and is the same at DC. Field strength is
potential gradient. The field close to the surface of a round wire
carrying a given charge per unit length is inversely proportional to the
radius of the wire. Thus field concentration and the risk of breakdown
always occurs near sharp edges or points. A rough engineering
approximation for more complicated structures is to think of the field as
proportional to one over the radius of curvature of a structure component.
That's why much of the metalwork of high voltage equipment has smooth
rounded edges.

You can visualise it in terms of field lines (lines of flux) being more
crowded together near a feature of small radius. High electric flux
density implies high field strength since the two are proportional to each
other, the constant of proportionality being called permittivity.


Its years since I studied this aspect but from memory the bundle of
conductors "looks like" a single larger conductor with an effectively larger
diameter and thus a reduction in stress/corona is achieved. Someone else
might be able to recall better from less aged studies? The 4 conductor
bundles associated with 400kV are relatively easy to visualise this but 275
kX with 2 conductors must "look like" an oval I suppose.
As a matter of interest I had a tour round Drax power station about thirty
years ago and the primary connections between the station and the grid
switching breaker farm were run in single heavy bars for a short distance.
The noise of frying air molecules was astounding.

Thanks John. Your explanation was better in helping me understand why
separating the conductors would have an effect.

I had a staff tour around Fawley many years ago. We didn't go out to the
transformer room as the guide said he didn't like being out there ! We did
get to open up one of the furnace inspection windows to feel the heat coming
off it (did you know furnaces are hung from the roof to allow expansion
downwards and outwards?). I've also worked for a few days in a coal station
in Notts. The noise around the ball mills can only be described as
mind-numbing.

--
NOBODY expects the Spanish Inquisition!

On Fri, 7 Oct 2005 08:06:43 +0000 (UTC), John wrote:

snip

Its years since I studied this aspect but from memory the bundle of
conductors "looks like" a single larger conductor with an effectively larger
diameter and thus a reduction in stress/corona is achieved. Someone else
might be able to recall better from less aged studies? The 4 conductor
bundles associated with 400kV are relatively easy to visualise this but 275
kX with 2 conductors must "look like" an oval I suppose.
As a matter of interest I had a tour round Drax power station about thirty
years ago and the primary connections between the station and the grid
switching breaker farm were run in single heavy bars for a short distance.

Quite possibly relatively thin-wall hollow bus-bar sections.

Nobody has yet mentioned skin effect (until now).....



--
the dot wanderer at tesco dot net

The Wanderer wrote:

On Fri, 7 Oct 2005 08:06:43 +0000 (UTC), John wrote:

snip

Its years since I studied this aspect but from memory the bundle of
conductors "looks like" a single larger conductor with an effectively larger
diameter and thus a reduction in stress/corona is achieved. Someone else
might be able to recall better from less aged studies? The 4 conductor
bundles associated with 400kV are relatively easy to visualise this but 275
kX with 2 conductors must "look like" an oval I suppose.
As a matter of interest I had a tour round Drax power station about thirty
years ago and the primary connections between the station and the grid
switching breaker farm were run in single heavy bars for a short distance.

Quite possibly relatively thin-wall hollow bus-bar sections.

Nobody has yet mentioned skin effect (until now).....

They are solid copper running at around 22kV from the generator to the
generator transformer but these are totally out of sight in normal
operation. On the HV substation itself they use hollow copper or more
usually nowadays aluminium - but I'm not sure if you can really call
100mm diameter and 20mm wall thickness tubing "thin wall"

Occasionally on 132kV sites overhead line cable was also used as a
flexible busbar. Most new switchgear (and busbar) installations are
metalclad using sulphur hexafluoride gas as insulation. They occupy a
fraction of the land area of an air insulated site.


--

On Fri, 07 Oct 2005 18:22:50 +0100, Matt wrote:

The Wanderer wrote:

snip

Quite possibly relatively thin-wall hollow bus-bar sections.

Nobody has yet mentioned skin effect (until now).....

They are solid copper running at around 22kV from the generator to the
generator transformer but these are totally out of sight in normal
operation. On the HV substation itself they use hollow copper or more
usually nowadays aluminium - but I'm not sure if you can really call
100mm diameter and 20mm wall thickness tubing "thin wall"

Occasionally on 132kV sites overhead line cable was also used as a
flexible busbar. Most new switchgear (and busbar) installations are
metalclad using sulphur hexafluoride gas as insulation. They occupy a
fraction of the land area of an air insulated site.

Ah! I guessed someone would be along to air their knowledge!

Hmm, let's see, fault levels should be worth a bit of discussion....

:-)

--
the dot wanderer at tesco dot net