link box (switching boxes) on pavements

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Hi all, I know this is probably not the best site for this kind of question but I will ask anyway because some of you might know.

here goes. I live in an estate with around 250 houses and their is a substation in a large grey box in the car park behind the flats across where I live. first of all I know domestic wiring inside out but I am interested to know how it is set up before it enters the houses.

anyway about half up the street there is a box on pavement marked "electric supply", having done some research I discovered this was a link box but how is it connected?.

for a few years now at the top of the road there are new houses being built (different estate) where there is also a slightly larger substation in that area. infact it has always been been there before the new houses were built.

But I will get to the point without boring you all too much, recently there are more houses being built in this new estate. and a guy from edf energy guy was in our estate and opened up this link box and he pulled out a cast metal housing I never actually saw what was beyond that. then about half an hour later he wen't over to the substation in our street (the one in the car park not the one in the new estate).


So finally here comes the questions

1 how does this link box "electric supply" work?.
2 do both substations from our street and the new estate meet at this link box?.
3 is the substation connected to this box?
4 how does the substation in our estate connect all the 250 houses in our estate?

btw in relation to question 4 when the guy was in our substation I had a look in the substation and on the lv side of the transformer there was only 2 large black 3 phase cables (probably 300mm per phase) plus 2 earth cables. is it likely/possible that those cables will supply all 250 houses in our estate without turning into molten.

Any understanding of this would be deeply appreciated thanks. I know you might find this question unusual but I am very interested in electrics.

ps I hope you can read this. sorry if it doesnt make much sense. thanks
 
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I know next to nothing about the high voltage side of it so I'll leave that one to the experts.

However on the low voltage side from transformer to houses, I'd say yes those 2 cables are likely to be the lot. The DNOs employ a much greater level of diversity than we sparks do in their calculations, typically only allowing 3kw or even less per house as an "expected load". They also work to a higher current rating per sq mm of cable than we are allowed to.

Very very roughly, I'd expect the transformer in there to be rated for a bout 1MW, which would give you about 1.45 kA per phase output. The two cables would probably be fused at about 800A per phase
 
The Link boxes are probably a means to isolate or connect sections of the supply grid when it is necessary to temporarily reconfigure the network. Re-configuration may be needed as a work around of a fault in a cable or for planned maintenance work.
 
Hi thanks for the replies so far, I have got a better of how the substation connects to all the houses at least. let me know If I have got this correct, the two 3 phase lv cables (plus the 2 earths) coming out the transformer will serve around 120 houses each. (40 houses per phase). and the way its connected is the main 3 phase cables from the transformer run along the street past the houses, and from the main cable there are few dozen joints, each joint serving 2 or 3 houses. does all this sound corrrect?

does all houses shared the neutral and the earth and get there live seperately from one of the 3 phase?. is this correct?


So having done further searches I am still lost to how the link box is actually connected. is this link box connected to the substation?

thanks like I say I am very interested but in a good way:)
 
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let me know If I have got this correct, the two 3 phase lv cables (plus the 2 earths) coming out the transformer will serve around 120 houses each. (40 houses per phase). and the way its connected is the main 3 phase cables from the transformer run along the street past the houses, and from the main cable there are few dozen joints, each joint serving 2 or 3 houses. does all this sound corrrect?
There is no single method employed everywhere. Sometimes the main distribution cable runs along the street and the feed to each house is tapped directly from it at junctions along that main route. Sometimes a spur is tapped off to another junction more convenient to a group of homes and the individual feeds to each home are taken from there. It all depends upon the layout and, to some extent, the methods which were currently employed by the area electricity board or the private company as the case may be at the time it was installed.

does all houses shared the neutral and the earth
Yes, although the number of distribution systems which actually have a separate neutral and earth is becoming less and less as the years go by. In many cases (and for newly installed mains, all cases now) the neutral & earth are combined.

and get there live seperately from one of the 3 phase?. is this correct?
Yes, by far the majority of British homes have a single-phase supply which means that the feed is tapped from one of the phase conductors and the neutral. In a given area, the load of the various homes is distributed as evenly as possible between the phases. Some larger homes, or homes with very heavy loads may have a 3-phase supply.
 
Link boxes basically are used to provide a way of being able to get the lv network fed from a different substation to enable maintainance work to be done - ie back feeding a substation via the LV network to enable the HV supply to be turned off for work to be carried out.
A link box can be either:
Two way- two main cables, 3 links (RYB)
3 way- three main cables, one pot ended cable not used, 3 sets of links (RYBx3)
4 way- four main cables, 4 sets of links (RYBx4)
6 way- 6 main cables, 6 sets of links (RYBx6)

Normally, they are used as an 'open' point between substations for this purpose.
In fault conditions where say the RED phase has been lost halfway along the cable between the substation and the linkbox on the other end of the cable, meaning that say 3/4 houses on the road are off supply, the fault can be backed via the linkbox with a 200a fused link which will get supplies restored.

It is a good way of setting out the network to ensure things can be moved about and customer down time minimised.

Hope this helps
 
thanks guys that has cleared that up. so the way it works is both substations meet at this link box on the lv side. so for example if the wanted to work on our substation, they would place the relevant links in that box so the houses still have power. That makes sense.

just one more thing then I will be out your hair. I take it the hv side of the transformer (I guess the 11kv feed and out) (the 2 big red cables on the other side of the transformer) are connected in parallel from other substations around the area? .thanks

one again I appreciate the advice and am more than happy to learn new things.
 
just one more thing then I will be out your hair. I take it the hv side of the transformer (I guess the 11kv feed and out) (the 2 big red cables on the other side of the transformer) are connected in parallel from other substations around the area

Sort of 'parallel' yes ... its actually a ring. In fact, this is a proper 'ring main' (as opposed to the ring final in your house). The red 11kV cable runs in a loop, visiting several subs & returning back to the origin. Each transformer is connected by a 'Ring Main Unit' which basically looks like a 'T' switch such that the transformer primary can be fed from the clockwise feed, the anti-clockwise feed to both. This system is again to allow redundancy and to allow the ring to be split into two radials in the event of a fault.

The 11kV distribution network is three phase only. The neutral is not distributed - the transformer primaries being wired in delta between the phases.
 
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It's also worth mentioning that while by far the majority of local distribution in the U.K. is 11kV now, there is still a small amount of 6.6kV in a few places.
 
Sort of 'parallel' yes ... its actually a ring. In fact, this is a proper 'ring main' (as opposed to the ring final in your house). The red 11kV cable runs in a loop, visiting several subs & returning back to the origin. Each transformer is connected by a 'Ring Main Unit' which basically looks like a 'T' switch such that the transformer primary can be fed from the clockwise feed, the anti-clockwise feed to both. This system is again to allow redundancy and to allow the ring to be split into two radials in the event of a fault.
To add a bit ...
Typically the "ring" will be run as two radials, with one switch somewhere being left open. If there's a fault, then they can open/close switches to isolate the fault and to feed the otherwise isolated section from "the other direction". The two ends of the ring may even come from separate boards in the 33/11kV substation.

Locally, they've recently put a new 11kV distribution board in, and before it got "switched on" I got a tour of it. There's two 132kV feeds in, two separate 132/33kV transformer sets (with tap changers), and two 33/11kV transformer sets feeding the new board - it's one of the sites where there are both on the one site which I gather can have "interesting" problems. The board itself is in two halves - each fed by one 33/11kV transformer. Then each ring goes from one side, round the ring, and back to the other side of the board. In normal use, each ring is two radials, fed from separate boards. If there's a transformer failure, then there's a link that can join both sides of the board to run from one transformer - so a lot of flexibility.
And being a new board, it's all remotely monitorable and switchable by design - unlike some of the older stuff that's had to have basic control and monitoring added on.
Remote monitoring and control is a big thing these days - it's all about having a better view of the network, and getting supplies restored as quick as possible.

At the 11kv/415V substation, it'll typically have the ring main unit with the base of the T feeding the transformer - one or both of the RMU switches may be remotely controlled (again, will allow some supplies to be restored remotely if there's a fault). On the output side, there'll be a cabinet with several sets of fuses - each supplying a distribution cable which in many cases may end up either at a separate substation or back at the same one if there isn't a convenient other substation to take it to.

Each case will be different. Local practices will have an effect, but other than that there is great variation in how things have evolved, what supplies are needed, and some of it comes under the category of "we wouldn't do it like that if it wasn't already there".
 
Oh yes, and I gather there are now some trials running involving leaving the rings permanently connected. If the tap changers are all set correctly then it doesn't create large circulating currents - but it does have a significant effect on fault protection.
But it does allow for the taps to be changes to deliberately create circulating currents. The idea is that when there are spikes in supply*, or short dips in load, the excess can be taken up by warming up all the distribution cables a bit.

* <cough>windmills<cough>
 
Remote monitoring and control is a big thing these days - it's all about having a better view of the network, and getting supplies restored as quick as possible.
In rural areas the DNO's are using radio-controlled sectionalizers more and more to enable faults on the 11kV network to be isolated more quickly from a distance and power restored quickly to those on unaffected feeders. Here's an installation in progress from near to where I used to live, must have been about 7 or 8 years ago, possibly a little more; you can see the antenna for the control receiver mounted on the left of the pole in the second picture.

NewRem1.jpg


NewRem6.jpg
 

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