ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Transformer Systems

Just one comment: European practice is to use three-phase transformers, not three single phase transformers. They also tend to be large and pad mounted, unless serving only a small number of houses.

The advantage of a three-phase transformer is the lower total cost.

The advantage of single phase transformers is that you can have the same transformers for both single phase and three-phase lines. The more single phase lines per three phase lines (on the LV side) you have, the more likely you are to go for this solution.

That goes for the U.K. too. We have single units for 3-phase delta-wye MV-LV xfmrs, like this pad-mount type:


or this pole-mount unit:

(Both of these are 11kV delta primary, 240/415V wye secondary.)

Single-phase transformers are normally used only where a single-phase 240V service is required for one or two isolated houses.

Re "distributed neutral" -- I'm refering to the situation where MV distribution is 3-phase 4-wire, so that a neutral is run along with the phases, thus enabling a 3-ph xfmr to be connected either delta or Y on the primary (and single-phase xfmrs to be connected either between two hot phases or from phase to neutral).

In my travels, it is only in the U.S.A. where I've seen a distributed neutral on MV lines. Admittedly my travels on this side of the Big Pond are restricted to the U.K., France, Ireland, and Spain.

Could it be that your rules are just specifying a wye system on the LV secondary side? That seems much more likely.

Delta LV supplies seem to have been a particularly American system.


[This message has been edited by pauluk (edited 08-06-2003).]

I have informed myself further and it seems that I got it wrong. All MV/LV xfmrs are here Delta/Wye. Sorry for the misinformation.

Belgian,
Over here, Y/D(or D/Y, depending on which sort of supply you are after) transformers form the bulk of our Distribution system.
D/D transformers are used on really long stretches of line, as a voltage stabiliser and these are normally run through some sort of an automatic tap-changer.
Just a note about transformer earthing, regardless of where a tranny is installed, it has to be earthed by a driven earth stake, this earthing is regularly tested.
According to ECP 35 over here, the use of the Earth Potential Neutral as a common between the LV and MV sides of a transformer, is to be avoided, because of the very real risk of back-feeds.