ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Pole mount XFMR

The cables taking off to the left supply a farm straight across the road from this, there is another pole supporting these cables, but the 5th wire isn't carried on from there. I'll take a picture when i'm along there tommorow

The fifth wire may have been a separate earth, the system being TN-S. Reasonably common practice years ago although significant disadvantage in possibility of loss during storm. It is not employed any more, at least here in the north of ireland but it can still be seen.

Has anyone considered the possibility that it could be an earth wire (TNS earthing system).
I have seen this arrangement on a small number of rural supplies where there is only a handfull of consumers.
I saw it recently when doing an upgrade, the incoming PoCo supply was split-concentric cable, with separate neutral & earth, not jointed at the cut-out. I traced the cable to the pole outside, there were L,N & E wires on the pole & I could see the house service terminated to these.
The lines on the pole were fairly old (1950's) but the drops to houses had been renewed with split-concentric cables.
I think the ground in the area is very rocky, so achieving the impedances for PME may have been difficult.
The PoCo here used to call these supplies C.E.W. (Continuous earth wire).

It's a possibility, although I don't think I've ever come across an overhead TN-S system in the areas in which I have lived.

i also can't imagine that they would separate neutral and ground for overhead lines. the 5th wire as street lighting supply is common here.

In a few of our older, rural networks here an Overhead Earth wire is necessary.
The ground way out up towards the mountains, consists of rocks, stones and very little actual soil, trying to get a decent earth contact is pretty much impossible, even with a buried Grid system you still don't have a low enough resistance to trip the protection in a reasonable time frame to ensure personal protection.
Most of these systems have been replaced with a Buried system that goes very deep down into the ground and uses huge bare copper/steel rods, the last one we drove was 14m long.
Oddly enough Ryan, are those spikes below the Secondary fuses, some sort of an anti-climbing protection?.
{Message edited to add last question. }

[This message has been edited by Trumpy (edited 10-31-2003).]

Guys,
How come there is no protection (Fuses) on the Lineside of the Transformer?.
Unless they are at the other end of the Spur line.
I was always taught to install Primary fuses above the Transformer, where the HV droppers come down to the Xformer, this is done for convenience and saves the Lines crews or Faults staff having to go and find the fuses, which in some instances has to be done quickly.

Yes. The brackets have four short arms spaced at 90 degrees with barbed wire run between them. You can see the idea a little better in this photo:


It's not standard practice to use primary 11kV fuses at the xfmr here, and you'll see the HV lines just tapped and run straight to the xfmr all over the place:



[This message has been edited by pauluk (edited 11-01-2003).]

Just to add that you will see means of isolation in a few places.

Here's the incoming 11kV which feeds a large part of Bush Estate where I live. The feed goes underground for about the last 100 yards before arriving at a pad-mount xfmr in a fenced sub-station:





[This message has been edited by pauluk (edited 11-01-2003).]

Paul,
In your last pic, that is an ABS (Air Break Switch.
There is no fusing in these bits of gear they are just a switch, as I am sure you are aware.
Just a note on the cable head, to the right of the ABS, where the 11kV heads underground.
Over here in NZ, we would have to have an XLPE cable taken up to the level of the cable-head there and sealed with a Heavy Duty Heatshrink Boot and sleeves with Arc flash preventing cowlings on each Phase.
And where a feed heads Underground or returns to terminate at a pole, the wires must be sleeved with Heatshrink to denote the Phase Rotation of the 11kV supply.
Don't get me wrong Paul, I'm not having a go at you or your Line-workers, in the UK.
Line-work is hard enough to do, without some idiot poking jibes at you!.