Odd Electrical Distribution Systems

[richardash1981]

RE post 42, an interesting picture, thanks for posting. Single phase transformers of that size are rare, I don't think that I have ever seen one like it.

Neither had I, or my colleagues! Thankfully our equipment works without making any assumptions about voltage phase angles!

 

My earlier remarks regarding the need for one transformer needing to be of reversed polarity, were in reference to old street mains intended for 3 wire DC and the need to supply AC via such mains. This requires that each 3 wire main be supplied with about 500 volts between outers and 250 volts between each outer and the neutral. This requires the use of either a pair of three phase transformers, one with reversed polarity, or a single diametric transformer as earlier described.

I think that's what this transformer does, but all the mains from this substation are in phase with each other (so no-one can get a three phase supply). As the load is terraced housing and a large primary school I don't suppose any of them are too bothered about not getting three phase supplies. Because the board is a replacement you can only see the 1961 cables used to connect it up, not the original street mains, in the substation.

In theory, THREE of the transformers illustrated in post 42 COULD be used. Connect one third of the existing 3 wire mains to each transformer. Connect the 11Kv primaries so as to balance the load between phases. first transformer between phases A and B, second one between B and C and the third one between A and C. Never heard of this being done though.

I think this is how the area where the photo was taken is wired, except that the three transformers are in different substations - so each substation is single phase, but the substations are distributed around the three phases of the 11kV ring main as described to even up the load at the primary. It can't do much for the 11kV losses however! Certainly the 11kV ring switchgear in this sub was three phase, but as the plate shows only two of the wires go to the transformer.Confusingly, the operations people on the ground call this a "two phase" network, but it is really single phase! If this is the case there must be no way to get a back-feed from adjacent substations, because they would all be 120 degrees out of phase ... There are apparently pockets of this round Leeds, presumably quite a bit of DC power (or single phase AC) got wired before standardisation, and has never been wholesale replaced.

[sunray]

Confusingly, the operations people on the ground call this a "two phase" network, but it is really single phase!

I believe it is 2 phase. If it was single phase (in the sense of N to L = 240V) then the PD acros L1 & L2 (or L & L' or whatever is in force) would be zero. I you looked at the 2 L's on a scope you will see 2 supplies with a phase shift, it just happens to be 180^o instead of the usual 120^o.

 

What would you describe 6,9 or 12 supplies equally spaced? We always call them 6, 9 or 12 phase. I see no reason to exclude 2 phase from this list.

I know this has been argued time and time again though.

 

[richardash1981]

What would you describe 6,9 or 12 supplies equally spaced? We always call them 6, 9 or 12 phase. I see no reason to exclude 2 phase from this list.

I know this has been argued time and time again though.

That transformer rating plate says "single phase", which was what I had picked up on. I suppose I would expect a 2-phase supply to have the phases at 90 degrees so you can run a (self-starting) induction motor from it, which would be unequally spaced (but could be made into four equal spaced with a pair of inverted windings). Wikipedia takes this view, calling what we have been talking about (with 180 degree shift) Split-Phase power. You certainly want to know which you have got if you intend to connect to more than two wires from it!

[sunray]

We always call them 6, 9 or 12 phase. I see no reason to exclude 2 phase from this list.

I know this has been argued time and time again though.

That transformer rating plate says "single phase", which was what I had picked up on. I suppose I would expect a 2-phase supply to have the phases at 90 degrees so you can run a (self-starting) induction motor from it, which would be unequally spaced (but could be made into four equal spaced with a pair of inverted windings). Wikipedia takes this view, calling what we have been talking about (with 180 degree shift) Split-Phase power. You certainly want to know which you have got if you intend to connect to more than two wires from it!

 

 

So getting back to my question, which I'll abrieviate What would you describe 12 supplies spaced at 30^o?

 

Next questions

What would you call a supply that uses phases 1, 5 & 9 from above.

What would you call a supply that uses phases 1, 5 & neutral

 

. Wikipedia takes this view, calling what we have been talking about (with 180 degree shift) Split-Phase power.

Ah yes but who placed the entry on there?

Edited July 22, 2019 by sunray

[adam2]

The generally accepted international way of describing AC supplies is to list the number of current carrying conductors (excluding protective earths) and the number of phases. as follows.

 

Single phase 2 wire, as used d0m3stically in many places. Also used to describe 2 wire circuits derived from any multi phase system.

 

Single phase 3 wire, as used in the USA at 120/240 volts and less commonly in the UK at 240/480 volt. Sometimes called "split phase" in the UK.

 

two phase should be reserved for true 2 phase systems, with 90 degrees phase angle between phases. Believed extinct in the UK. Still used to a limited extent in the USA. Comes in 3 wire and in 5 wire.

 

3 phase, 3 wire. Little used in the UK at utilisation voltages. Most high voltage UK systems are 3 phase 3 wire.

 

3 phase, 4 wire. Widely used for households and light industry throughout the world. Common voltages include 120/208, 240/415, and 277/480 volts.

 

Systems with more than 3 phases are almost unknown. TRANSFORMERS with a 6 phase output are relatively common but are largely confined to feeding rectifiers when DC is desired. 6 phase or any other number of phases beyond 3 is virtually unknown for a distribution system. Note that the "diametric transformers" to which I referred earlier should strictly speaking be called "3 phase, 7 wire" no one does, they are called "6 phase" which is not consistent with the above but is the accepted terminology.

 

 

 

[sunray]

two phase should be reserved for true 2 phase systems, with 90 degrees phase angle between phases.

 

3 phase, 3 wire. Little used in the UK at utilisation voltages. Most high voltage UK systems are 3 phase 3 wire.

 

I have never encountered 90^o phase shift with any electric supply, other than the I/c 3ph supply to the building being incorrect and causing motor overloads to trip. That took a lot of effort to convince the energy supplier that they had a problem, even seeing it on a scope.

I do of course know of the 'capacitor start' system (although this is also a false description).

In industry 3ph 3w is used extensively, but I wouldn't like to make a statement whether 3W or 4W it more frequent, I provide far more motor circuits (3W or 6W) in control panels than 4W circuits.I've often worked on what is, or has been, described as 2 phase in industrial/control applications and make sure I confirm what they mean before providing such, looking back through my notes to 2014 I have found 17 occassions:

6] 48V or 24V with CT Neutral(earth)

4] 240V with CT Neutral/earth (usually 60Hz)

2] 480V with CT Neutral(earth)

2] 110V with CT Neutral/earth (standard 110V)

2] Single phase 400V derived from 2 phases of a standard 3ph supply.

1] Two phases and neutral derived from 2 phases of a standard 3ph supply.

The bracketed number being the number of times noted. This does not indicate the number of times I've worked on a format, just the times I've had to double check.

 

 

Systems with more than 3 phases are almost unknown.

 

Working in the 'Controls environment' I've encountered 6,9 & 12 phase on enough occassions to not refer to them as 'almost unknown'.

 

I'll happily accept the majority of them, if not all, are privately generated. Either their own generators or electronicallymechanically from the mains supply.

Edited July 24, 2019 by sunray

[adam2]

True 2 phase systems with a 90 degree phase angle were never popular in the UK and are probably now extinct.

 

Used to be a bit more popular in the USA but now rare. As an historical note, the large hydroelectric plant at Niagara falls originally produced 2 phase, and at 25 cycles rather than the more common 60 cycles. Lower frequencies used to be favoured for electric motors including railways. In Belgium they still use 16.66 cycles for some railways. Frequencies of less than 50 cycles are unsuitable for lighting, especially d0m3sticaly.

 

 

 

[AdrianW]

True 2 phase systems with a 90 degree phase angle were never popular in the UK and are probably now extinct.

 

Used to be a bit more popular in the USA but now rare. As an historical note, the large hydroelectric plant at Niagara falls originally produced 2 phase, and at 25 cycles rather than the more common 60 cycles. Lower frequencies used to be favoured for electric motors including railways. In Belgium they still use 16.66 cycles for some railways. Frequencies of less than 50 cycles are unsuitable for lighting, especially d0m3sticaly.

 

 

Isn't the channel tunnel "2-phase" using Scott transformers? I remember reading an article in the IEE mag (as it was then) about the power supply arrangements & I'm sure I read that it utilised the Scott configuration to derive the supply to the two running lines.

[adam2]

The channel tunnel uses single phase at 25Kv nominal for each running line. I presume that a center tapped 50Kv supply is used with the center tap earthed and connected to the running rails. One pole of the center tapped supply to each overhead wire. Thus each track and each train thereon receives a standard 25Kv supply, but the use of 50Kv distribution reduces resistance losses.

 

I would be very surprised indeed if true 2 phase, with a 90 degree phase angle was used on a modern project. True two phase is believed extinct in the UK and becoming rare elsewhere.

 

 

 

[richardash1981]

The channel tunnel uses single phase at 25Kv nominal for each running line. I presume that a center tapped 50Kv supply is used with the center tap earthed and connected to the running rails. One pole of the center tapped supply to each overhead wire. Thus each track and each train thereon receives a standard 25Kv supply, but the use of 50Kv distribution reduces resistance losses.

That would be an accurate description of what is called "autotransformer" electrification in the UK, but as that design was first used on the Great Western electrification, I have to presume it wasn't for the Channel Tunnel! Actually for this the tracks are all in phase, but there is an ancillary conductor (along the support poles) with the antiphase on it, and the titular autotransformers located to couple the power across.

 

I would be very surprised indeed if true 2 phase, with a 90 degree phase angle was used on a modern project. True two phase is believed extinct in the UK and becoming rare elsewhere.

As a public supply I would agree. But for the Channel Tunnel traction problem it's a wonderful fit (and nothing is actually supplied with two phases, just with single phase derived from them).

 

 

What you need are two large single phase supplies, one for each tunnel. You need a single supply for each tunnel so you can have the whole tunnel on a continuous wire for reliable fast running. You don't care about the relationship between the two tunnels, because they only meet at the ends, where trains are moving slowly (low power, and having a dead section for the voltage gap is less of an issue). You could wire both tunnels on one phase, but that would be a massive unbalanced load on the 3-phase grid. Next step would be to put one tunnel on each of two phases (so L1-L2 and L2-L3). This is better, but only 50% better because L3-L1 is still not loaded. The Scott transformers are a really clever idea. You put three-phase in and get two-phase at 90 degrees out. But what is magic is that if your two-phase load is equal (i.e. same current on each pair) then the three-phase input current is also balanced.

 

Now railway loads are never nice and constant, so you don't get balance, but you do at least get closer to a balanced grid load. The channel tunnel is probably a good candidate because largely identical trains run at largely fixed intervals, so the loads on the two tracks are likely to be similar much of the time. A three-phase connection like this could incur smaller connection costs than if you just went for a single phase traction connection. Against this you have to weigh the costs of the Scott transformers themselves, and the need to split the traction infrastructure into two electrically separate blocks.

The IEE paper might be this one? https://ieeexplore.I.../document/64683 I got it from the references of another paper modelling the harmonic and load variation impact of conventional vs. Scott supplies for rail, which claimed to show that a much weaker grid node could be used to power the Scott version.

 

 

The business of 16.66 cycles was to allow large "universal" type motors (the sort in your traditional vacuum cleaner or electric drill) to be run on AC with acceptable brushgear life (the arcing gets worse as frequency rises). These were the only motors suitable for rail traction (because they could run at variable speed) before mobile rectifiers became an option post-war. So practical railway electrification before 1950 had to either be DC (maximum about 3kV practical because you can't step it down to the motors, so lots of substations) or low frequency AC (15kV commonly, but either with dedicated power plants or rotary converters to get 16 2/3 cycles). Changing the latter is mostly in the "too hard" box, so Switzerland and surrounding areas also have a lot of low frequency AC systems, largely fed from dedicated hydro power in the alpine regions.

[andy™]

 

 

You don't care about the relationship between the two tunnels, because they only meet at the ends, where trains are moving slowly

 

the channel tunnel has 2 large crossover points where trains can change tunnel. there will also be seperate overhead sections so they could isolate a section of tunnel for maintenance. so it would be easily possible to split each section between phases

[Jivemaster]

IIRC one of the London Underground lines runs at 33 and a bit hertz -Better for traction motors that really prefer DC, but easily transformed with somewhat larger transformers than 50Hz.

[adam2]

IIRC one of the London Underground lines runs at 33 and a bit hertz -Better for traction motors that really prefer DC, but easily transformed with somewhat larger transformers than 50Hz.

 

 

DC is used throughout the London underground for traction.

 

London underground used to have, and may still have a 33.3 cycle AC supply for signalling and other purposes. I can remember when this was used for emergency lighting at Earls court underground station. The main lighting was by large modern HID lamps mounted at high level and presumably supplied from AC public mains.

 

In addition, smaller incandescent fittings were mounted at low level (only just out of reach) along the platforms, these used the 33.3 cycle supply.

 

Before the war, London transport owned a large mansion block near Baker Street station. This was supplied from their own 33.3 cycle system and found little favour with the residents as this frequency is rather low for lighting, especially d0m3stically.

 

 

 

 

[Brian]

This topic has been split from the CEEFORM colour topic.

[adam2]

This topic has been split from the CEEFORM colour topic.

 

Thankyou for that.

 

We had drifted rather off topic, but at least it was not religious, political, or d0m3stic.

 

 

 

 

 

 

Before the last war, many different voltages and frequencies existed in the UK.

 

DC for lighting and power was usually 3 wire at anything from 420 volts to 500 volts between outers, though some 2 wire systems existed. DC for traction was usually 500 to 550 volts for tramways. The Southern railway used 650 volts, later increased to 750 volts.

 

AC for domestic or industrial use used almost any voltage in the 100 volts to 250 volt range and could be derived from three phase or other systems. Frequencies included 15 cycles, 16.3 cycles, 20 cycles, 24 cycles, 25 cycles, 40, 50 and 60 cycles.

 

The government commissioned a report known as the Weir report after the chairman of the committee Mr Weir, later Lord Weir.

 

This recommended that all new small supplies should be at 240 volts, single phase, 50 cycles, with an earthed neutral and usually derived from 3 phase 4 wire systems at 240/415 volts. And that larger supplies would be 3 phase at 240/415 volts also with an earthed neutral.

 

240 volts was chosen as being about highest voltage already in general use. There was relatively little 250 volts in use. 50 cycles was chosen as being the highest frequency already in general use. There were systems operating at 60, 80 and 100 cycles, but not many. 50 cycles was also about the minimum for d0m3stic lighting.

 

Existing DC systems and non standard AC could remain in use, and minor extensions and additions could be made to such systems, but all new systems were to be at the new standard.

 

Implementation was much delayed by the war, and by immediate post-war shortages of labour and materials, but eventually was achieved.

 

After the war, the 13 amp fused plug system was adopted for d0m3stic and similar purposes. These plugs and sockets were only to be used for 50 cycle AC supplies at 220/240 volts and with an earthed neutral. Where legacy DC systems, or AC at non standard voltages or frequencies remained in use, the older BS 543 plugs and sockets were to be used. The presence of a 13 amp socket was meant to indicate the presence of a standard supply into which a non technical person could pug anything with a matching plug.