ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Republic of Ireland/N Ireland distribution/transmission lines questions

Just to address the title of this thread a little better here is a picture of a rural 110kV distribution line in NI that runs from substation to substation.
In damp conditions this line will 'sizzle' quite loudly and the corona discharge can be seen jumping the insulators!



And a close up.



Martin.

See the SWER topic by RODALCO just a couple of threads down this same category Non US systems and Trades.

Primary voltage here is 11 kV. Return path through earth at HT side.

Secondary at service transformers 230 / 460 Volts.
or 230 - 0 - 230 Volts.

I will post a few more SWER piccies next month while in the Coromandel, New Zealand.

Cheers Ray.

Most high tension lines here (110kV, 220kV etc) will "sizzle" during very damp conditions.

Irish drizzle can produce some unusually difficult conditions for electrical installations. You basically get a dense fine mist of rain that can cause all of the above effects.

Also, some of those 110kV lines in N.I. are probabally from the same era (they look simlar) to the very oldest parts of the national grid in the Republic. It's very unusual to see a corona, even on the oldest bits of the network though.

It's the same basic arrangement at the transformer, just with 240/480 instead of 120/240V. The difference is that in the U.S. the majority of homes get the full 3-wire service providing 120 and 240V whereas in Britain -- as Martin pointed out -- each house will just have its usual 2-wire connection for 240V.

There may be some farms or other larger installations which have the full 3-wire service and share the load though.

Yes, and in fact until quite recently I hadn't realized just how many of these were around my local area. After I spotted the first I kept a look out and realized that there are quite a few.

That's due the the rural nature of the area and the communities which have a number of homes spread out along a road.

As soon as you get into a place with a larger cluster of services, you'll find a full 3-phase 240/415V distribution system. You won't find either the basic 2-wire 1-ph or 3-wire 240/480V xfmrs in built-up areas.


They can be wired either phase-to-neutral or phase-to-phase in North America. They have a much greater variety of distribution voltages and arrangements than here, and in some cases a transformer with a specific primary voltage can be used phase-to-phase on one system or phase-to-neutral on another.

In the U.K., we never distribute a neutral conductor on HV lines, so a single-phase spur has to be run as two phases, as in the pictures above.

With the much greater distances in North America, presumably the savings on insulators and xfmr bushings by running as one phase plus neutral can be considerable.


[This message has been edited by pauluk (edited 01-13-2006).]

Sorry but I haven't got it completely.

As I see just four wires, does this mean HV and LV share the neutral (grounded) wire or is it just not visible?

In France for example even a LV neutral is regarded as an active conductor and is always isolated.

Here with us distribution is always 3 wire, usually IT (often with inductive starpoint to connection to earth).

The strangest thing about that topic is that I have never taken care of those poles as here where I live and work just everything is buried in the ground including phone, cable tv and the 20kV distribution. Only exception is 110/220kV feeding from the power station.

We are so to say more or less a pole free zone. Nevertheless there are quite a few places that have overhead connections elsewhere in Germany.

That American system would be a phase-neutral system, with the neutral shared with the LV system. Such is typical in urban areas.

I have never seen a Phase-Phase service transformer for single phase service.

.classicsat

Very common in rural New Zealand.
The primary HT side is taken of any 2 phases from the 3Ø line.
The secondary is either 230 - 0 - 230 Volts, so 460 Volts is available at the outer 2 terminals at 180° phaseshift , or both secondary windings are parallelled up to have 230 volts at double amperage.

for Wolfgang. at the primary there is one insulator visible in this case, photo from MartinX
and the return is via the earthed transformer tank. HT current return through earth only.
at the secondary 120 - 0 - 120 is available, in case of MEN the neutral is earthed. The secondary current loop is completed within the secondary windings from the transformer.

To feed a 1Ø SWER line an isolating transformer is required at the start of the SWER line e.g. 2Ø 11 kV to 1Ø 11 kV SWER and return path through a very good earth otherwise the feeder would trip on earthfault all the time.

Since I've never been "off contininent", I've only see NA setups, which I should clarify I haven't seen (at least residential) single phase phase-phase esystems here.

Yes, I realize that most of the world, at least the British colonies use 11KV delta.

Weren't some of the older distribution networks in North American cities ungrounded deltas? (e.g. 2400V).

Single-phase xfmrs would have to have been phase-to-phase on those.