Re: 208/240V, was: 25Hz power

Thank you for the great write-up. My father was a power EE, and I had

> worked some as an electrician, so I have picked up some of this info > over the years. I especially remember my father describing the > high-leg delta connection when I was a kid, but I never ran into one > in practice.

I understand from my Stateside friends who work in commercial settings that the high-leg delta catches some people out quite often. They've reported more than one or two odd cases in which someone has added a circuit breaker to that B-phase for a regular 120V branch circuit, not realizing that they're actually getting 208V.

> On the primary side of these transformers, everything here is >> connected between phases. In fact NONE of our HV lines have a neutral >> run with them, so three-phase primaries are always delta-connected, >> and the primary on a single-phase transformer is connected across two >> phases of the HV. That primary supply to the final transformers is >> almost always 11kV (measured phase to phase), although there are still >> a very few local distribution networks operating at 6.6kV in a couple >> of areas. Thus a single-phase HV spur line has to be run as two "hot" >> phases. > Is the generator end wye-connected for a ground (earth?) reference, or > is there ground fault detection circuitry on delta connected > generators? Or is ground reference / ground fault not as big a > concern there as here? Just curious.

Yes, the lines are referenced to ground/earth at source. The generator or transformer secondary which is FEEDING the line will either be wye configuration with a grounded neutral point, or I think sometimes they'll use a delta configuration but add auxiliary wye windings to provide the ground reference point. The same goes for much of Continental Europe. The ground on the neutral of the HV system is sometimes via a low-ish impedance rather than being solid though.

That's as far as the HV neutral goes here though. Transmission and distribution is then just 3-wire 3-phase with delta-connected primaries.

Srandard phase-to-phase voltage levels in Britain are 400kV, 275kV,

132kV, and 66kV for longer-distance transmission, then 33kV and 11kV for more localized distribution. As mentioned before, the older 6.6kV local systems can still be found, but are now very rare.

When it gets down to LV, we have much less choice than in North America. Either single-phase 240V or 415Y/240 3-phase, plus the

240/480V 3-wire in a few rural areas.

Compare that with the U.S. 120/240V 3-wire, 240V delta, 240V "high-leg" delta, 480V delta, 208Y/120V, 480Y/277V, etc., not to mention Canadian 600Y/347V.

> As noted before, in Continental Europe 3-phase supplies into homes are >> very common, however, and to British and American minds they seem to >> take 3-phase to extremes. In France, for example, it's not at all >> uncommon to find a small house which has a full 3-phase 4-wire >> 380Y/220V service, with the main breaker set to just 15 amps per >> phase! Arranging heating and cooking loads on a service like that can >> be quite a juggling act. > I can imagine. Is something like an electric range connected to 380? > Is it wired single phase or three phase? > They commonly wire ranges 3-phase wye.

The elements are still just 230V, connected phase-to-neutral, but they distribute the load between phases, e.g. two rings on phase A, oven and one ring on phase b, grill/broiler and another ring on phase C. These days we often have the same models on sale in the U.K. as in Europe, and they come with a 4-way (plus ground) terminal block for the supply connection. In England, we just strap L1-L2-L3 together and connect to our single-phase 240V service on a 30 to 40A branch circuit.

In Europe, they'd feed it as 4-wire 380Y/220 on a 16A 3-pole breaker. French electrical systems especially are what you might call "interesting." EDF (Electricite de France - the main supplier there) has tariff structures which are quite needlessly complex, and they have a basic standing charge which is dependent upon the maximum rating of the supply and which rises rapidly at higher levels. Hence many places try to get away with supplies which are considered ludicrously low-power by American/British standards, and not helped by the 3-phase service which then makes it hard to keep what little load can be connected evened out. (Just ask any Brit who has tripped out breakers in France trying to use his trusty 3kW electric kettle for making tea!)

They even have complicated sensing and switching systems for electric heating, designed to disconnect water/space heating loads when power is drawn from a general-purpose branch circuit to avoid exceeding the limit and tripping the main breaker. Some tariffs also have a highly complex system of red, white, and blue days, combined with day and night rates giving no less than six different per-unit costs for the same supply.


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Paul Coxwell
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