Life in the UK

[Taj]

The national distribution system in the UK is six-phase delta at 132 kV, coming down to three-phase delta 33 kV or 11 kV locally. That is then distributed by a variety of different systems:

Three-phase star or delta 440V for industry.

Three-phase star local distribution at nominal 440V with individual premises taking single-phase-and-neutral at 240 V from one of the three phases, with the load roughly balanced between premises so as to minimise the current in the neutral (saves copper).

Two-phase local distribution using only two of the available phases and neutral from the above three-phase system. Individual streets use different pairs of phases, so as to balance the load on the three-phase system. (Uses available cables from older two-phase and D.C. distribution systems.)

Two-phase local distribution at 480V centre-tapped with individual premises taking single-phase-and-neutral at 240 V from one of the phases, with the load roughly balanced so as to minimise the current in the neutral. (Mainly found in small villages as it allows the use of a cheaper local supply transformer with a single-phase primary connected across two of the phases of the three-phase 11 kV delta system.)

In all domestic premises the only supply available to the consumer will be nominal 240 V single-phase with neutral and a separate earthing pin. Most UK socket outlets and all lighting circuits have a single switch in the live, the neutral is not normally switched. Until legislation forced the use of insulating sleeves on the roots of the plug pins, it was just about possible to touch the live pin when withdrawing the plug, so people of my age have the ingrained habit of switching off the socket before changing plugs. Some domestic equipment is permanently connected to an outlet box, and in this case both the live and the neutral must be switched.

Please explain six phases on a delta circuit. I'm puzzled how that works.

[hoborob]

I would presume that it differs from the 3 phase system which has 3 power conductors that are 120 degrees out of phase with each other with the line voltage measured for one leg to another for the high voltage and line to Neutral in the Wye configuration for the lower voltage. I am supposing that 6 phase uses a similar measuring system but has 6 power conductors with each separated by 60 Degrees from each other. I may be incorrect about that but to an Electrician/Electronics guys it sounds right to me.

[Taj]

The national distribution system in the UK is six-phase delta at 132 kV, coming down to three-phase delta 33 kV or 11 kV locally. That is then distributed by a variety of different systems:

Three-phase star or delta 440V for industry.

Three-phase star local distribution at nominal 440V with individual premises taking single-phase-and-neutral at 240 V from one of the three phases, with the load roughly balanced between premises so as to minimise the current in the neutral (saves copper).

Two-phase local distribution using only two of the available phases and neutral from the above three-phase system. Individual streets use different pairs of phases, so as to balance the load on the three-phase system. (Uses available cables from older two-phase and D.C. distribution systems.)

Two-phase local distribution at 480V centre-tapped with individual premises taking single-phase-and-neutral at 240 V from one of the phases, with the load roughly balanced so as to minimise the current in the neutral. (Mainly found in small villages as it allows the use of a cheaper local supply transformer with a single-phase primary connected across two of the phases of the three-phase 11 kV delta system.)

In all domestic premises the only supply available to the consumer will be nominal 240 V single-phase with neutral and a separate earthing pin. Most UK socket outlets and all lighting circuits have a single switch in the live, the neutral is not normally switched. Until legislation forced the use of insulating sleeves on the roots of the plug pins, it was just about possible to touch the live pin when withdrawing the plug, so people of my age have the ingrained habit of switching off the socket before changing plugs. Some domestic equipment is permanently connected to an outlet box, and in this case both the live and the neutral must be switched.

By saying six phase delta are you meaning three phases on parallel conductors? Delta systems are three phase, hence the designation "delta."

Also, for orange apple, you might not find the Euro 240v hot pot any more powerful than the American at 120v. The missing factor being the resistance. Either voltage can be configured to draw the same power. A typical hot pot in USA might be 1200 to 1500 watts. It would be reasonable to assume the foreign unit might be built drawing roughly the same wattage for the same task regardless of voltage.

Hoborob, I couldn't find the post that you responded to earlier this evening and rewrote mine. Might have had something to do with getting an emergency call in to work and being in a hurry. At any rate, I've worked with some three phase European power that was industry standard, specifically wind turbine systems generating about 2MW at 690V - which is transformed to whatever system voltage is required. I'm hard pressed to think of an instance in common usage that would be 6 phase. Not saying it doesn't exist, just wouldn't be delta.

[pelmut]

Please explain six phases on a delta circuit. I'm puzzled how that works.

You can think of it as two linked three-phase delta systems skewed by 60 degrees from each other or as a centre tapped three-phase star system with the neutral point floating (only 6 conductors in the transmission line instead of 7).

I'm hard pressed to think of an instance in common usage that would be 6 phase. Not saying it doesn't exist, just wouldn't be delta.

Apart from long distace power transmission, I can't think of a delta example. There are plenty of examples around of six-phase star because it is used to power rectifier sets for large DC loads where minimum ripple is an advantage. The six-phase is derived from the centre tapped secondaries of a transformer running on an ordinary three-phase supply; six rectifiers are used with the return current being fed back into the centre tap. Typically a broadcast transmitter power supply or a traction sub-station would use that system because the transformer is already necessary, so the extra cost of having it centre-tapped would be minimal and there would be a great saving on the chokes and capacitors in the smoothing filter with double the ripple frequency and half the initial ripple amplitude of a standard three-phase system.

[Stevie D]

Thanks for correcting and enlarging upon my idea of a three-phase system. I'm learning a lot from this thread!

...
(I heat water in a hot pot then brew the coffee in a French press.)
...

What's a 'French press'? Is that what we call a cafetière?
Or is it what is used to print Le Monde?
I suppose it could be a French wrestling move...

[trainspotter48]

As someone who worked in the UK electricity supply industry for many years, I would like to add my twopenceworth on this.

Generation is almost inevitably on a 3 phase, star connected machine. The UK runs at 50Hz, so a 2-pole machine is running at 3000 rpm. The star point is earthed, and the 3 output lines (at voltages varying from the 690v outlined for wind turbines up to around 25Kv for a 500/660Mw steam turbine) are then fed to the delta winding of a transformer to step up to the required transmission voltage (275Kv or 400Kv). (Wind turbines and 'small' solar farms will probably feed into the local 11Kv network.) For convenience, the transmission lines normally run overhead on lattice steel towers (pylons) with one (3 phase) circuit on each side of the tower.
Eventually this is transformed back down to 132Kv, 33Kv and 11Kv for distribution. Each network will establish an earthed neutral in order to allow the protection circuits to operate correctly. The 11Kv network will then be run to the local ground or pole mounted transformer to support the local 400/230v network (400v between lines, 230v between line and earthed neutral), which is distributed on a 3 phase 4 wire circuit.
There are exceptions to this, especially in rural areas, where it may be possible to find a 460/230v single phase supply, where the mid point of the transformer is earthed to effectively provide 2 single phase 230v supplies, at 180 degrees to each other.
In general it will only be motors or transformers that are connected across 2 or 3 lines with no earthed neutral connection.
Lighting and 'small power' loads then run at 230v (+5 -10%) from one of the lines.
A typical house supply is provided through a 100A 'service fuse' to the meter and then on to the customer's 'consumer unit', where large loads such as a cooker or electric shower will have a dedicated circuit, while the socket outlets are fed as a group from a 32A fuse or circuit breaker, with the individual plugs containing a fuse (ratings range from 3A to 13A) to protect the flexible cord and appliance.

The only place that I have ever come across 6 phase is on the secondary of a transformer supplying a rectifier.

Hope this helps.

John

[Orange Apple]

Thanks for correcting and enlarging upon my idea of a three-phase system. I'm learning a lot from this thread!

...
(I heat water in a hot pot then brew the coffee in a French press.)
...

What's a 'French press'? Is that what we call a cafetière?
Or is it what is used to print Le Monde?
I suppose it could be a French wrestling move...

Could be all of the above but the one I was referencing is http://target.scene7.com/is/image/Targe ... &fmt=pjpeg (not endorsing Target; just found a handy image there.)

[Taj]

Thanks Pelmut and trainspotter48. That clears things up a bit. I haven't run into any six phase in the US, nor was it discussed in any of my classes. I'm guessing it's more in use "across the pond." Is it safe to assume that the linked deltas would also have two wild legs? We have tested wind turbines of various electrical configurations where I work, but not being a PhD EE scientist I don't get every detail. Our most common machines generate at 480, 690, or 4160 which we step up to 13.8kv to the distribution grid. Our local xmission systems run 115kv and 230kv. They have a rather large DC xmission setup in California. They use lots of power along the left coast.

[Reaper_Man]

just to point out that in the UK the nominal voltage is 230 Volts and not 240 (it was 240 up until 1993), the UK Government agreed to harmonization at 230V on 9th March 1993. this was done to bring the UK in line with the rest of Europe

[Orange Apple]

just to point out that in the UK the nominal voltage is 230 Volts and not 240 (it was 240 up until 1993), the UK Government agreed to harmonization at 230V on 9th March 1993. this was done to bring the UK in line with the rest of Europe

Interesting. Did the 4% change have any impact on consumer electronics? How was the change actually implemented - was there a short countrywide outage while the distribution was adjusted? This seems like a small change but I cannot imagine the disruption that it would create in the infrastructure.

[pelmut]

just to point out that in the UK the nominal voltage is 230 Volts and not 240 (it was 240 up until 1993), the UK Government agreed to harmonization at 230V on 9th March 1993. this was done to bring the UK in line with the rest of Europe

Interesting. Did the 4% change have any impact on consumer electronics? How was the change actually implemented - was there a short countrywide outage while the distribution was adjusted? This seems like a small change but I cannot imagine the disruption that it would create in the infrastructure.

There was no change at all, they just kept the same voltage and slackened the tolerance limits, so it is now continuously 4% higher than the nominal 230v. Most post-war electronic kit in the UK was designed to work on any voltage from 200 to 250 (by manual selection in the past and automatically since the advent of switched-mode power supplies), so there was no impact at all.

[hoborob]

I can see the practicality of having a 6 phase distribution system but as a person that is used to see three phase systems it is sort of difficult to get your head around having 6 phases available. It does make sense to have all outlets set up on only 1 of the phases and thus having to use the full voltage of that phase. But when you start into using multi-phase systems the math gets really complicated. I myself would handle the system as two separate three phase systems and work it from there. If you somehow managed to get a phase reversal of only 2 phases in the 6 phase system it would likely require some advanced meters to isolate the reversed phases and the to fix it properly. In a three phase system you simply reverse to of the phases to correct a phase rotation problem.

As I said though I am simply not used to working with 6 phases and am very familiar with 3 phase systems. The US does not use a 6 phase transmission system anywhere that I know of. The highest transmission voltage used here as far as I know of hand is 750KV but I seem to recall an experimental 1MV system being put up somewhere in the western half of the country. I don't know if it ever occurred or not. The mainstay of the long distance system here is a 500KV line. I would tend to think that a 6 phase system of that voltage would be very hard to protect from arc-overs to the towers due to the amount of airspace required to insulate the conductor from a potential path to ground.

[pelmut]

As someone who worked in the UK electricity supply industry for many years, ...
For convenience, the transmission lines normally run overhead on lattice steel towers (pylons) with one (3 phase) circuit on each side of the tower.

It appears that I had erroneously assumed two three-phase circuits were staggered by 60 degrees, so as to give six-phases; the syymetrical physical spacing of the conductors* further reinforced my belief. In view of trainspotter48's better knowledge of the subject, I am quite prepared to accept that I made an incorrect assumption and the distribution network in actually three-phase. My apologies for posting an incorrect assumption.

*Spacing the conductors on the corners of an imaginary hexagon and feeding them with six phases would give a lower voltage between adjacent conductors than if they were two three-phase circuits.

[moonshadow]

Fascinating read! Six phases of power sounds pretty wild. It seems that if I were to have to spend some time over on the other side of the Atlantic, I'd be completely clueless!

'Round here most places I've worked in have 3PH wye, 208v with a neutral. Some of the older buildings have 3ph delta with the high leg. I believe all of our stores are either 208 or 480 wye. In the warehouse there is 3ph delta with high leg, that we have to be careful when we test equipment in there as some equipment is made to pull a control circuit right off one of the three phases, if it's a 120v control we have to make sure not to connect it on the high leg otherwise we'll blow every relay out in the machine!

I'm not really crazy about buildings that have a high leg.

All this talk about the high voltage power I found very interesting.

[pelmut]

Fascinating read! Six phases of power sounds pretty wild.

It's not that difficult to produce six phases from three, all you need is three centre-tapped windings on the secondary of a three-phase transformer.

Some of the older buildings have 3ph delta with the high leg.

"High leg" is a term I haven't heard before, could you explain what it means?