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).]
Re: 33-to-11kV Sub-station#141115 06/15/0410:05 AM06/15/0410:05 AM
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.
Re: 33-to-11kV Sub-station#141117 06/16/0406:56 AM06/16/0406:56 AM
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?
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.
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.
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).]
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?