Talk:Split phase

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[edit] Comments removed from the article

I've removed the following comments from the article as the discussion seems "closed".

Atlant 12:15, 22 Jun 2005 (UTC)

< ! - - i've heared someone refer to this as a "wild leg" is this the common term? Plugwash 21:36, 13 May 2005 (UTC) - - >

< ! - - Yes, it is, and here's my description. --Wtshymanski 14:01, 21 May 2005 (UTC) - - >

< ! - - UK experts, please comment.- - > (re 55 volt power)

< ! - - Comment on what? The above is all correct. - - >

[edit] I don't get it

from the article:

A transformer connected to a 3-wire distribution system has a single phase input (primary) winding. The output (secondary) winding is centre-tapped with a conductor called the neutral on the centre tap, which is normally connected to earth ground

I don't understand this part. May someone give another explanation or draw a picture? Great! --Abdull 13:01, 23 July 2005 (UTC)

Abdul, I need to establish a baseline here: Do you understand the concept of a transformer (say, a "filament transformer") that has an ordinary line-voltage primary and a centre-tapped low voltage secondary?
Atlant 00:10, 24 July 2005 (UTC)

[edit] Where does the "second" phase offset come from?

If I understand this correctly, the transformer is supplied to the primary winding with a single phase, higher voltage, and the secondary is tapped on both ends, giving 2 120V lines. What I dont understand is how these two lines are out of phase with each other. Or are they? I always assumed that you couldnt get a difference in potential between two 120V AC lines unless they were 90° out of phase with each other.

with split phase they are 180° out of phase. That is they are the exact inverse of each other. Therefore they can be obtained from the centre tapped secondry winding of a single phase transformer.

The question remains, How are they 180 degrees out of phase? The answer is simple: If you imagine the transformer standing vertically, the first phase is established by making the hot tap at the top of the transformer and making the neutral tap at the middle. Now if the second phase was established by taking the "hot" tap at the middle and the "neutral" tap at the bottom you would have two identical phases. But, note that the technique is to establish the second phase by making the hot tap at the bottom and the neutral tap in the middle, the same location of the neutral in the first phase. This creates a mirror image of the first phase (i.e. upsidedown). To prove this you may connect the second phase to an occiliscope twice. Once correctly connecting the hot and neutral to the scope, and once connecting them backward. You will see the phase flip. —The preceding unsigned comment was added by Canavair (talk • contribs) .

[edit] 230 V / 240 V

IMO we should change references to 240 V / 480 V to 230 V / 460 V in respect of European systems where the nominal voltage is 230 V. Anybody disagree? --Ali@gwc.org.uk 21:35, 16 October 2005 (UTC)

Go ahead if you wan't i don't have any particularlly strong feelings either way on this. Plugwash 00:59, 17 October 2005 (UTC)

Where the reference specifically is about what is in Europe, then of course 230 volts should be the voltage referred to since that is now the official standard (plus or minus 10 volts). But for split phase in general, the competing references would be to use either 120/240 as in the US and Canada, or 100/200 as in Japan, where this split phase system is dominant. When you do have a 3 wire circuit like this, the correct way to reference the voltage is with 2 numbers, e.g. 120/240. That's much like three phase, except it is common, though not exclusive, to put the lower voltage first. Three phase would almost always put the larger number first (and North Americans include "Y" in reference to Wye), e.g. 208/120 (US, Canada), 220/127 (Mexico), 380/220 (much of the world), 400/230 (Europe and much of the world), 415/240 (Much of the former British Empire), 480/277 (US commercial and industrial), 600/347 (Canada commercial and industrial), 690/400 (Europe industrial), and 1000/577 (US mines).

By the way, the reference in the article about using just 2 wires to get one voltage out of a dual voltage split phase system, e.g. getting just 230 volts from a 230/460 volt center tapped transformer, as being cheaper, is not really correct. If you happen to have the split phase system available, it is actually cheaper to go with three wires, assuming wire assemblies being equally available. The reason this is so is because you would only need half the current capacity. If you needed 100 amps of 230 volt power, that would require 2 wires that have 100 amp capacity in both, or 3 wires that have only 50 amp capacity in all three. The latter is a lesser total cross section of wire. The fundamental reason is because in part, the voltage is effectively higher (e.g. 460 volts). Perhaps the comfusion comes from comparing the European single phase system (2 wires, 100 amps each, just 230 volts) to the North American single phase system (3 wires, 100 amps each, dual 120/240 volts). The European system is the wiring cost winner when comparing the same amperage as the same maximum voltage. But if there is a 230/460 volt transformer there, then going with a 3-wire split phase system saves even more over both the 2-wire 230 volt system and the 3-wire 120/240 volt system because the wires can now be thinner. And 460 volts doesn't require much more in insulation nor is it much more dangerous (it's still 230 volts relative to ground). The North American 120/240 volt system can be, and is, used at 240 volts for many things, but is actually a bit safer for grounded contact because the voltage is not more than 120 volts relative to ground. It's only when one contacts both of the opposite "phase" wires that the higher voltage is involved. Skapare 01:37, 27 September 2006 (UTC)

[edit] Split phase is two phases

In my opinion split phase should also be called 2 phase because we create and utilize two voltage signals with respect to ground. These two voltage signals are out of phase by 180 degrees with respect to ground. The Thevenin equivalent voltage source must be defined as: L1 to N = 120V @ 0 degrees and L2 to N = 120V @ 180 degrees (or vice versa)

One could argue that L1 to N and N to L2 are in phase. But this would require a negative vector which is the same as a positive vector @ 180 degrees. Or it would require the definition of ground = zero volts to be void.

Unfortunately, by convention, it isn't named that way. While a computer engineer might speak of a "two phase clock" that operates exactly this way (two signals 180° out of phase), power engineers don't use this terminology. To them, it's only two-phase if the two phase legs are 90° out of phase. It's not necessarily logical, just the (universal) convention among the power engineering cognoscenti.
Atlant 15:33, 23 March 2006 (UTC)
It's only 2-phase if you can start an induction motor off it, without messing about with starting windings, capacitors, etc. - a very pragmatic definition. If it doesn't make a revolving magnetic field, it's not polyphase. --Wtshymanski 18:33, 23 March 2006 (UTC)
Actually the two windings on the secondary side are in phase and not out by 180°. If you go from the bottom of either winding (in the diagram) to the top of that same winding you get V @ 0°. It is only when you start at the N wire in the middle and go in opposite directions that it appears out of phase. In industrial settings it is very common to use transformers that are not just tapped in the center but provide two wires per secondary winding. This allows series or parallel connections.
The two windings are generally just one winding, anyway. It's around one core. Whereas in three phase power, the windings are separated to 3 legs of an "E" core, or 3 separate cores are used. Many "split phase" transformers actually have 2 separate windings with a total of 4 wires. They can be wired in series using the common point as a neutral as described by the article, or the 2 windings can be wired parallel to get the half voltage at double the amperage. Skapare 01:43, 27 September 2006 (UTC)

You can use the term "poles" in reference to the number of different phase vectors out from the neutral center point. This is what typical electricians and power engineers often use. Skapare 01:43, 27 September 2006 (UTC)

[edit] SWER systems, diagrams and an edit.

Editing notes

Sorry started out small and grew, hope you like the diagrams.

Removed 11KV from diagram, the primary voltage varies.

Created an image suitable for an international audience, as was image was obviously scanned from a book.

Neutral is always grounded, as written one gets the impression that the center tap is called neutral and the neutral may be grounded.

You can call the live conductors the ungrounded conductors, in the industry we refer them to as live, ungrounded may be clearer.

Changed the wording of the European example so it flowed on from the first, better for an international market.

Added the a reference to SWER lines ( my initial intent before I got carried away).

Removed the comment "The neutral conductor ensures that the voltages on the two legs do not get (far) out of balance". Doesn't belong in the paragraph covered better elsewhere.

Tried to internationalize the load comment.

Don't know where the 1/4 comes from, I could be wrong but I don't think I am. Diagrams created to make it clear in my mind. Could add another showing how the out of phase current subtract in the neutral conductor, oh well getting late.

The amount of copper is all about the total current carried.

Removed following; we are talking about copper not cost, why confuse the issue. "Furthermore, since smaller wires have higher costs per unit of area for insulation and installation labour, the costs won't go down by as much as the copper use, but the cost savings can still be significant."

Removed following; absolutely true but has little to do with this. "Voltage drop is generally the determining factor in cable sizing for long runs (whereas for short runs it is the cables current-carrying capacity rating)."

--Charles Esson 13:33, 15 July 2006 (UTC)
The primary reason for caring about copper use is the cost of the copper (which is one of the largest components of the cost of a cable) but it is not the only cost and more seperate cores means more insulation, more complex processing etc.

What a great system, the reason for the 1/4 is now quite clear, thanks. Charles Esson

If you double the voltage, you reduce the current to half to maintain the same power. So if you start at 240 volts and 200 amps, and change the voltage to 480 volts, now you only have 100 amps of current. That half current will now have a voltage drop across the fixed resistance of the same wire of half as many volts. If the voltage drop on the wire running some distance to feed a building from the transformer, when operating at 200 amps, is 4 volts, then at just 100 amps, that drop in voltage is only 2 volts. That means a transformer load in the building would be getting 236 volts in one case, or 478 volts in the other case. Reducing the 480 volt setup to a 240 volt setup with that transformer, you now get 239 volts (3 volts more than the 236 volts the other way). So doubling the voltage reduces the voltage drop to 1/4 as much, given a constant wire size. Typically, the wire size will be reduced to 1/2 the cross section, but that still reduces the voltage drop to 1/2 of what it would be at the lower voltage. Alternatively, the wire could be run a longer distance. Now consider the advantage gained by running the street distribution wires at 30 to 100 times the voltage. Skapare 02:01, 27 September 2006 (UTC)

[edit] image from transformer article

I added the image from the transformer artical because it is a split phase SWER transformer. It would be interesting to know where this was taken, if in the USA then SWER lines are being installed in the USA and the exception metioned in the SWER article are happening Charles Esson.

The photo details say it was taken in Canada. —The preceding unsigned comment was added by 61.9.139.165 (talk • contribs).
Actually it says "about 12 miles from Dunville Ontario" (which is presumablly a misspelling of Dunnville, Ontario), our article does not however give enough information on dunvilles location to categorically place the picture in canda. Plugwash 14:19, 18 July 2006 (UTC)
Single bushing transformers are used all over the place and so this does not mean this is an SWER installation. We can't see the overhead wires - could easily have a neutral conductor overhead. There is no point within 20 km of Dunnville Ontario that is part of the US according to Google Map. --Wtshymanski 17:51, 18 July 2006 (UTC)
looking at http://wearcam.org/christina/billru_cottage/d325.jpg which appears to be a larger view of the photo in the article and some of the related images on http://wearcam.org/christina/billru_cottage/polemount.htm it looks like the horizontal wire in the picture is a neutral of some kind with the phase wire being higher up on the pole. Plugwash 23:47, 18 July 2006 (UTC)

Yes I see your pointCharles Esson.

[edit] Used in Europe?

In the UK and Europe 230/460 V, 3-wire, single-phase systems are used to run farms and small groups of houses when only two of the three phase high voltage conductors are available (it is cheaper to run two wires than three). I dont know a motor or somethink other for 460V. Common is a 3 phase system with 2 voltages. For ex. 230/400V.

Its not used anywhere near as much here as 3 phase is but it certainly is arround (its generally used where they wan't to supply more than they think they can handle as single ended single phase but they don't wan't to bother with 3 phase MV stuff). As the article says though its pretty much unheared of to use 460V for anything and its normally split out into single ended single phase either before or as soon as it reaches the customer. Plugwash 01:13, 24 August 2006 (UTC)

[edit] It is the AC equivalent of the former Edison direct current distribution system.

How is this related to the Edison direct current distribution system?-Crunchy Numbers 18:13, 30 August 2006 (UTC)

A more correct title or term would be "split wiring system". There is nothing inherint in the wiring system that makes it specific to DC or AC. The sources would be different (a battery or rectifier system for DC, or a generator or transformer secondary for AC), but the concepts are essentially the same.

Think of wiring up a 12 volt electrical system in a small isolated cabin. You might use a marine deep cycle battery, trickle charged from a solar energy source, to run the system. You could double the system essentially just like Edison's 110/220 volt system, as a 12/24 volt system, and 3 wires. By adding only 50% more wire of the same gauge on the feed from the 2 batteries, you have doubled the system capacity.

Now suppose you install a generator that puts out 240 volts. You get a transformer that reduces that 240 volts AC to 2 separate secondary windings of 12 volts each. One of those windings would be good to operate the original 2 wire 1 battery system. But with the split phase 12/24 volt system on 2 batteries, you could run it from the transformer instead by wiring the 2 secondary windings together in place of the batteries just like the batteries were wired. As long as everything in the cabin doesn't care whether it gets AC or DC (incandescent lights and universal motors), it should work fine. Skapare 02:13, 27 September 2006 (UTC)

[edit] as with three phase?

"Houses in the UK normally only have single ended single phase power and so (as with three phase) only one active line and the neutral is taken to each house." As with three phase? what does this mean? --Gbleem 04:32, 2 September 2006 (UTC)

It means the same as when the cables in the street are three phase. Plugwash 17:22, 3 September 2006 (UTC)
I believe it means that in some places only 2 of the 3 phases are available on the street, and in other places all 3 phases are available. Larger homes that need a 240/415 volt supply may be typically provided with only 2 of the 3 phases, since there is very little real three phase need in a home. But a large electric stove may be designed to run on 415 volts to help keep the wires from having to be too large. The utility can cut costs by running only 2 phases on each street and connecting just 2 single phase transformers to provide the 240/415. The ratio of the voltages is the square root of 3 (approximately 1.732050807568877), not 2 as in the true single phase split system. Skapare 02:25, 27 September 2006 (UTC)
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