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How much current flows through pylons?



 
 
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  #1  
Old March 18th 17, 12:07 AM posted to uk.d-i-y
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Default How much current flows through pylons?

Despite extensive googling, there seems to be nothing that tells me how much current flows along wires on a national grid pylon. They only list voltages. Anybody know?
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  #2  
Old March 18th 17, 05:10 AM posted to uk.d-i-y
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Default How much current flows through pylons?

Well it depends on the load one supposes. It also then depends on the
voltage on thewwires as the whole idea of using high voltages is to reduce
losses due to disipation when the system is under load.
The answer basically is there is no answer.
Might find more if you asked the max current of the one at xx to yy.
Brian

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"James Wilkinson Sword" wrote in message
news
Despite extensive googling, there seems to be nothing that tells me how
much current flows along wires on a national grid pylon. They only list
voltages. Anybody know?



  #3  
Old March 18th 17, 11:18 AM posted to uk.d-i-y
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Posts: 2,305
Default How much current flows through pylons?

On Saturday, 18 March 2017 00:07:59 UTC, James Wilkinson Sword wrote:
Despite extensive googling, there seems to be nothing that tells me how much
current flows along wires on a national grid pylon. They only list voltages.
Anybody know?


A 400 kV National Grid circuit may carry 1 kA in each of its three phases, thus transmitting a power of 700 MW.
A 132 kV distribution circuit may carry 300 A in each of its three phases, thus transmitting a power of 70 MW.
An 11 kV distribution circuit may carry 150 A in each of its three phases, thus transmitting a power of 3 MW.
A 400 V final distribution circuit may carry 200 A in each of its three phases, thus transmitting a power of 150 kW.

(Remember, these voltages are phase-to-phase voltages, the phase-to-earth voltages are 1.73 times lower. Thus (400 kV/1.73) x 1kA x 3 = 700 MW.)

http://www.emfs.info/what/terminology/ (site maintained by National Grid)

[Pylon type] L12 is effectively the L6 replacement will take twin conductors up to 850mm2, but all aluminium conductor rather than the heavier steel cored kind formerly used.

http://www.gorge.org/pylons/structure.shtml

Owain


  #5  
Old March 18th 17, 12:05 PM posted to uk.d-i-y
NY
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Default How much current flows through pylons?

"newshound" wrote in message
o.uk...
On 3/18/2017 11:18 AM, wrote wrote:
Despite extensive googling, there seems to be nothing that tells me how
much
current flows along wires on a national grid pylon. They only list
voltages.
Anybody know?


A 400 kV National Grid circuit may carry 1 kA in each of its three phases,
thus transmitting a power of 700 MW.
A 132 kV distribution circuit may carry 300 A in each of its three phases,
thus transmitting a power of 70 MW.
An 11 kV distribution circuit may carry 150 A in each of its three phases,
thus transmitting a power of 3 MW.
A 400 V final distribution circuit may carry 200 A in each of its three
phases, thus transmitting a power of 150 kW.


200A per phase at 400V (240V phase-to-neutral) doesn't sound very high. We
have a 60 A "company fuse" and I presume our neighbours do too. With an
electric fire (3 KW), an electric shower (maybe 8 kW) and an electric oven
and hob (maybe 6 KW), you'd be getting towards that limit but still
remaining legal. Now imagine lots of people roundabout doing that. It
doesn't take many houses to run up 200 A - or a total of 600 A across all
three phases. How many houses are typically fed from a single feed from the
substation or 11 kV-to-400V pole-mounted transformer? What is the average
current that is assumed per house when sizing up the number of houses that
can be fed from one substation circuit? I presume it not the full 60A of the
company fuse rating.

And Supergrid pylons (400 and 275 kV) are normally double circuit, aren't
they? Three wires on each side of the "tree".


How much of the route from the power station to the consumer is redundant
multi-circuit? At one point, typically, does it change over to a given house
only being fed by one set of wires, and if that line develops a fault there
is no backup circuit?

Is there a backup route as far as the final substation that transforms to 11
kV or 400V, or is it higher up the chain?

I presume for maximum redundancy they try to use feeds from different places
rather than two sets of wires carried on the same pylons, in case an
accident takes out *all* the wires (both circuits).

I'm intrigued at the way house gets its electricity supply. There is
overhead mains on wooden poles (originally four separate wires, now a single
fat cable with four wires) and our house is the middle house of two adjacent
blocks of three houses. There is a single feed from the wooden poles to the
end of one block, and then four wires running along the back of one block,
overhead across the gap to the next block and along there, with each house
taking its feed from neutral and one of the three phases - I think no two
adjacent houses are on the same phase. I suppose this is less unsightly than
every one of the six houses having its own single-phase feed from the street
poles.




  #6  
Old March 18th 17, 03:57 PM posted to uk.d-i-y
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Posts: 993
Default How much current flows through pylons?

"NY" wrote in message
...

SNIP

How much of the route from the power station to the consumer is redundant
multi-circuit? At one point, typically, does it change over to a given
house only being fed by one set of wires, and if that line develops a fault
there is no backup circuit?

Is there a backup route as far as the final substation that transforms to
11 kV or 400V, or is it higher up the chain?

I presume for maximum redundancy they try to use feeds from different
places rather than two sets of wires carried on the same pylons, in case an
accident takes out *all* the wires (both circuits).

I'm intrigued at the way house gets its electricity supply. There is
overhead mains on wooden poles (originally four separate wires, now a
single fat cable with four wires) and our house is the middle house of two
adjacent blocks of three houses. There is a single feed from the wooden
poles to the end of one block, and then four wires running along the back
of one block, overhead across the gap to the next block and along there,
with each house taking its feed from neutral and one of the three phases -
I think no two adjacent houses are on the same phase. I suppose this is
less unsightly than every one of the six houses having its own single-phase
feed from the street poles.




They always used to rotate phases down a street, so (say) phase 1 - house
1, phase 2 - house 2, phase 3 - house 3, then phase 1 - street lighting,
phase 2 - house 4 and so on down the road to balance the load between
phases.

We have the 11 kV to 415 v transformer on our land and are the first 'drop'
of single phase at the farmhouse, but also take the three phase into the
barn at 160 amps per phase. No street lighting though round here. The 11 kV
can be fed from two points - we have an overhead HV line and an underground
HV cable, but normally only one is active.

Andrew

  #7  
Old March 18th 17, 07:22 PM posted to uk.d-i-y
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Posts: 4,252
Default How much current flows through pylons?

Andrew Mawson was thinking very hard :
They always used to rotate phases down a street, so (say) phase 1 - house 1,
phase 2 - house 2, phase 3 - house 3, then phase 1 - street lighting,
phase 2 - house 4 and so on down the road to balance the load between
phases.


So as to as best they can, balance the load on all three phases, so as
little current as possible appears on the neutral line.
  #9  
Old March 19th 17, 06:26 AM posted to uk.d-i-y
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Posts: 288
Default How much current flows through pylons?

On 18/03/2017 15:57, Andrew Mawson wrote:
"NY" wrote in message
...

SNIP

How much of the route from the power station to the consumer is
redundant multi-circuit? At one point, typically, does it change over
to a given house only being fed by one set of wires, and if that line
develops a fault there is no backup circuit?

Is there a backup route as far as the final substation that transforms
to 11 kV or 400V, or is it higher up the chain?

I presume for maximum redundancy they try to use feeds from different
places rather than two sets of wires carried on the same pylons, in
case an accident takes out *all* the wires (both circuits).

I'm intrigued at the way house gets its electricity supply. There is
overhead mains on wooden poles (originally four separate wires, now a
single fat cable with four wires) and our house is the middle house of
two adjacent blocks of three houses. There is a single feed from the
wooden poles to the end of one block, and then four wires running
along the back of one block, overhead across the gap to the next block
and along there, with each house taking its feed from neutral and one
of the three phases - I think no two adjacent houses are on the same
phase. I suppose this is less unsightly than every one of the six
houses having its own single-phase feed from the street poles.




They always used to rotate phases down a street, so (say) phase 1 -
house 1, phase 2 - house 2, phase 3 - house 3, then phase 1 - street
lighting, phase 2 - house 4 and so on down the road to balance the load
between phases.



Yep, and it's not uncommon to see that in multiples of houses. So you
may have 4 houses next to each other on phase one, the next 4 on phase 2
etc.

A far more common variant (on properties built in the late 1960's and
early 1970's) is house 1 and 2 on phase 1, house 3 and 4 on phase 2 and
house 5 and 6 on phase 3.




--
Adam
  #10  
Old March 19th 17, 07:19 AM posted to uk.d-i-y
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Posts: 18
Default How much current flows through pylons?

On Sat, 18 Mar 2017 12:05:12 +0000, NY wrote:

200A per phase at 400V (240V phase-to-neutral) doesn't sound very high.
We have a 60 A "company fuse" and I presume our neighbours do too. With
an electric fire (3 KW), an electric shower (maybe 8 kW) and an electric
oven and hob (maybe 6 KW), you'd be getting towards that limit but still
remaining legal. Now imagine lots of people roundabout doing that.


It's called Diversity. The DNO's know that everything will not be plugged
in at the same time, so their network will cope for the vast majority of
the time (and time has proven this, as there are very few blackouts
caused due to DNO substation fusing blowing).Short term overloads dont
stress the system too much, as can be seen on christmas day - when 50% of
houses have their ovens on etc - but 50% of them are gas,then the oven is
not on full power apart from the first 5 minutes, so the load isnt as
much as you think
I was told the typical demand for each house when the network is designed
is around 5 to 10 amps.That'd give 120 houses to one substation feed at 5
amps - that seems about right.
 




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