Here are a few pics I snapped today of a sub-station in the nearby town of Hoveton. This enclosure has two sets of 33kV feeders entering from the left, and transforms down to 11kV for distribution around the town. The 11kV outputs are mostly fed underground to nearby poles and to ground-level 11kV-to-240/415V xfmr stations.

Sorry I couldn't get any closer for greater detail.





Notice the insulator stack set at an odd angle on the incoming 33kV lines to get the phases in the right positions. This is the last pole at the enclosure before the lines drop down to the switchgear:

The incoming feeders are actually supported by rather unusual and very high lattice towers just before reaching the sub-station, which is behind me across a parking lot in this picture:


Part of the reason for the high clearance can be found just behind that clump of woodland. The lines cross part of the Norfolk Broads, and the spacing between supports is fairly long to get across the large area of water. You can see the tops of those towers just poking above the trees here:


The sub-station itself is located right behind the main railway station, pictured here.


[This message has been edited by pauluk (edited 06-10-2004).]

A couple more items left on my disk from the same photo session.

Here's the cell-phone site located right next to the sub-station:



And a 240/415V metering and switch cabinet alongside the railway line:


Sorry, the photo of the cabinet labeling didn't come out too well on my cheap camera, but this one is providing power for the "Wroxham Points Heaters," now displaying the modern yellow-triangle warning sign in place of the old red and white danger notices:

Great Pictures, Paul!.
Just looking at that 4th picture.
That sort of pole is called an angle pole here, where the lines do not enter or leave the pole at right angles on either side.
But, one thing I couldn't help but notice, may it is my bad eyesight, but is there a link between the centre and the RH phases on that pole?.
You could actually place that sub-station
in New Zealand and no one would be any the wiser, it looks almost identical to the ones we use, although our fences are made of wire mesh, topped with razor wire.
On the subject of Cell-phone sites,
I had the oppurtunity to work at the Vodafone tower during it's upgrade, a couple of years back.
And I must say, them transponder arrays are HUGE when they are down on the ground.
The maintenance crew there, winched one up onto the tower, it took them ages.
Even the co-axial cable that the guys were using looked strange, it was about 35mm diameter and the centre of the inner conductor was hollow.
A bit like a shielded refrigeration pipe!.
And here was me with my little 4mm2 3C+E wire for the Stand-By generator.

This is the arrangement I was referring to, rather than the fact that the lines go off at an angle.

There's an insulator mounted vertically on top of the cross-arm which supports a link connecting the incoming center-phase over to the right. Then there's another insulator lower down at a funny angle on the right-hand pole which supports the link connecting the incoming right-hand phase onto the center wire down into the sub-station.

If you look closely at the left-hand phase, you can see a straight link hanging down just connecting straight through.

The second feeder on the pole that's just clipped off the right side of that same photo has the identical arrangement: LH phase linked straight across, RH and center phases transposed.


That's thanks to "skin effect." At these sorts of frequencies RF current tends to travel mostly along the outside of a conductor, so they can economize on materials and save weight by using a hollow center conductor.



[This message has been edited by pauluk (edited 06-16-2004).]

Paul — Your fourth picture with 33kV spans looks like there are four bell insualtors per deadeand, where in the US I would normally expect to see three. Is this in an area subject to saltspray or lots of fog?

Paul,
Am I correct then in saying that your HV system is run as R-B-Y, over most of it's length and then when it is fed into a sub-station, it is changed to the standard phase rotation of R-Y-B?.
This system is used here, Not sure why the system isn't just run in R-Y-B all the way through.

Not being an HV lineman, I'm afraid I can't answer that one. Maybe some of our other U.K. members know the answer? I'll keep a look out at any other sub-stations and take a look if I get a chance.

BJ,
Not sure about the standard number of insulators in this application either I'm afraid. The area where this sub-station is located is a few miles inland, so there shouldn't be a salt problem. As for fog, it's no more prone than any other area, although it's possible that in certain weather the humidity may be a little higher than average due to the Broads surrounding Hoveton ( The Broads is a large expanse of inland lakes and waterways).

Of course, this being England there always tends to be a little more damp in the air here than you'd be used to in California anyway.

For comparison, here's a standard 33kV line running cross-country (sorry, it's not too clear for showing the insulators):



[This message has been edited by pauluk (edited 06-17-2004).]

Will the new harmonized colour changes to Brown /grey/black affect the transmission side? or is it only the M.V thats changed.

Good question Alan. I can't see any reason why 11kV and above would be changed. As our transmission/HV distribution voltages aren't "harmonized" across Europe, there seems little point in changing the color coding of them to match.

But then to me, there seems little point in changing the 240/415 coding either, so who knows?

I believe that our phases are arranged as R-Y-B.

All the 11kV poles around here have small coloured plates about half way down the pole, with the phase colours arranged on them that way.

Await some pictures.

I must correct my statement. Four bell insulators for “35kV-class” lines would be routine here too.

If the 11Kv poles currently have RYB markers, I would have thought that if new ones are installed or replacement takes place they will follow the L1 L2 L3 Format or Brown,Black,Grey. I thought we has some link with Europe anyway on the HT side,

The present red/yellow/blue markers can still be distinguished fairly easily even when well-weathered after being out in the British climate for many years.

If we do change on HT, then I don't see brown/black/gray being anything like as easily distinguishable. That alone seems like a good enough reason to me to retain our existing RYB system.

I work in the north of england.A while back someone told me that phase rotation is incorrect in merseyside. Id forgoten till I did a 3-phase ac in chester. On completion the unit would not run. When i checked rotation it WAS incorrect, therfore I swapped 2 phases at the origin and hey presto! Has anyone heard of this before, does it exist anywhere else and how did hit happen in the first place?
Thanking you!

Can not quite get to grips with what your saying there Teach. as part of an overall network can not imagine how Mersyside can have different phase rotation to the rest of the U.K. The consequenses dont bare thinking about.

It seems highly unlikely that there could be a big phase-rotation problem over a large area of the network. The large number of interconnects on the HV transmission system would surely make this impossible.

I'd say it's more likely that the phase identification could be wrong within a small area, e.g. a neighborhood 11kv-to-240/415V xfmr incorrectly wired.

Even then though, you'd have to have two phases "crossed over" for there to really be a problem. Just "rolling" three around in sequence would be unlikely to cause any trouble.

For example, if R-Y-B is cross-connected to Y-R-B, there is a problem. But if R-Y-B is connected as Y-B-R, the phases won't correspond with others in the district but motors will still turn the right way as the rotation is still essentially correct. just with all phases displaced by 120 degrees compared to the correct wiring.

I take on board what you say guys
Im just a contracting animal and know little about supply. Since its happened to me ive mentioned it to a few people and it seems to be well known of up this end
While we talk supply id love to know something about this.....
When i look at a pylon i see three sets of wires RYB- right. Also there appears to be an earth wire connecting the tops of the pylons. Now my question is this ,where is the neutral. I assume the network must be in delta and the end of use substations are delta/star?
thanking you all in anticipation!

The British HV system doesn't distribute a neutral, so as you say, the primaries of transformers are wired delta. (Or tapped across two of the three phases for single-phase, such as to feed one or two remote houses.)

This is somewhat in contrast with the North American arrangement where in many systems a neutral is distributed, thus allowing single-phase transformers to be wired phase-to-neutral or phase-to-phase.

Running a single-phase branch as one phase plus neutral to a remote point has certain economies, both in the pole equipment and in the fact that the 1-ph transformer needs only a single high-voltage bushing.

The line economies may well add up when you consider that the North American network has to cover many more miles into much more remote territory than anything we have in Britain.

thanks paul
now the next thing is this....
If they are wired in delta that would mean they are electrically separate from earth,so whats the point in earthing the pylons.Am i right in thinking that there would be no potential to earth???

I can think of two reasons:

- The pylon will remain there even after a lightning strike.

- If a conductor touches the pylon, the current to earth/ground (the soil) is sufficient for the ground fault protection to intervene.

I think C-H has it. On British systems, it's the big all-metal suspension towers used for 132kV and above which have the ground wire strung between them. Lower voltage distribution lines such as 11kV and 33kV which are generally run on wooden poles don't have it.

It's possible to run a 3-phase network with no neutral and delta-connected transformers at the load ends but still have the originating end wired with a wye secondary.

In that case the system can still be referenced to earth by having the star/neutral point of that secondary grounded (either solidly or via an impedance). So if you ran an 11kV 3-wire line that way, each of the distributed phases would be at about 6.6kV to earth.

Even if the transformer feeding the line is delta wired, the phases can still be balanced to earth by the use of auxiliary windings with a center-point earthed.

Finally, even if the transformer is delta and no attempt is made to ground the system at all, you'll still get variable voltage readings from phases to earth due to capacitance along the route.



[This message has been edited by pauluk (edited 07-05-2004).]

It used to be the case that transformers of different vector groups were used on distribution systems.

The majority of our network was constructed with DY1 transformers, but there are numerous areas which still have DY11. When replacing a DY11 transformer where we cannot re-align the phasing as there are 3 phase customers being fed off the transformer, we use a DY1 transformer but swap the yellow and blue phases on both the HV and LV sides.

There are areas of the UK distribution network where there are a variety of different vector group, and this might explain the different configuration of the OHL.

Ian

Edited to correct spelling etc

[This message has been edited by ianh (edited 07-06-2004).]

Ah.... That sounds interesting.

Do you have any more info on when these different trnasformers were installed?

Not to hand, but I believe that it has been down to the distribution company. Some companies might use DY1 whereas others may use DY11. Some might still use a combination of the two. As far as I know both types are still available.

The choice of vector group makes no difference to the operation of the system, until you end up trying to parallel the two!