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General => General Technical Chat => Topic started by: Fried Chicken on September 26, 2026, 02:56:31 am
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I mean for all intents and purposes...
If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?
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If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?
Yes, it is only 120VAC to ground on either line, that's one of the main points. It's like a center-tapped transformer vs one without the CT. How that affects a particular situation or device depends on a lot more specific information. But if you have an isolated heating element or insulated motor then those devices won't know the difference provide the insulation is rated for a few kV as it should be.
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I mean for all intents and purposes...
If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?
Not sure just what you're asking here.
No, it's not the same as 240V to ground;
Each phase is 120 volts to ground.
Since the phases are 180° opposed to each other, there's 240 volts between the phases.
But you already knew that.
The only similarity between 240V split-phase and your notional "240V to ground" is ... 240 volts.
But in the case of the split-phase power ground is inbetween the phases.
So I'd say no, no mathematical or technical similarity.
Have to see what others say here.
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In US, the 240v is 1ph end-to-end transformer. You then center tap that and jam that tap into the earth. The center tap creates two inline coils where each coil creates 120vac(rms). Two in series creates (from the mag field) the 240vac(rms) end-to-end.
A "split" or tap could be done anywhere. If you wanted 60v and 180v then you tap it that way, it's still 240v end-to-end.
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In US, the 240v is 1ph end-to-end transformer. You then center tap that and jam that tap into the earth. The center tap creates two inline coils where each coil creates 120vac(rms). Two in series creates (from the mag field) the 240vac(rms) end-to-end.
A "split" or tap could be done anywhere. If you wanted 60v and 180v then you tap it that way, it's still 240v end-to-end.
A couple of years ago a fault developed at the transformer at the road, and I had one phase 140V and the other phase 340V!
Surprisingly few things cared, either way. Mostly on the low voltage side the coffee machine pump wouldn't run, and the oven took an hour to come to pizza temperature instead of 15 minutes.
I had one cheap Chinese wallwart let out magic smoke, and there was a POP in my 3 weeks old dehumidifier and it stopped working. I took it back to the Noel Leeming store (not even the same one I'd bought it from actually) and said nothing and they had it fixed for free in 2 or 3 days.
Someone from the lines company came and pulled the fuses on the low voltage side and replaced them and then everything was back to normal. And they scheduled the same on the 11kV side as apparently they hadn't been changed in 40 or 50 years.
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In US, the 240v is 1ph end-to-end transformer. You then center tap that and jam that tap into the earth. The center tap creates two inline coils where each coil creates 120vac(rms). Two in series creates (from the mag field) the 240vac(rms) end-to-end.
A "split" or tap could be done anywhere. If you wanted 60v and 180v then you tap it that way, it's still 240v end-to-end.
A couple of years ago a fault developed at the transformer at the road, and I had one phase 140V and the other phase 340V!
Surprisingly few things cared, either way. Mostly on the low voltage side the coffee machine pump wouldn't run, and the oven took an hour to come to pizza temperature instead of 15 minutes.
I had one cheap Chinese wallwart let out magic smoke, and there was a POP in my 3 weeks old dehumidifier and it stopped working. I took it back to the Noel Leeming store (not even the same one I'd bought it from actually) and said nothing and they had it fixed for free in 2 or 3 days.
Someone from the lines company came and pulled the fuses on the low voltage side and replaced them and then everything was back to normal. And they scheduled the same on the 11kV side as apparently they hadn't been changed in 40 or 50 years.
Shouldn't that have had all your RCD/RCBO/GFCI's tripping?
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Shouldn't that have had all your RCD/RCBO/GFCI's tripping?
why should it ,theres no imbalance just over voltage
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I mean for all intents and purposes...
If you have 240v split-phase AC (as is common in the U.S.) is that mathematically, or technically any different than 240v to ground?
If you ignore the grounding considerations, then 240 V AC is 240 V AC. There is no difference at all. However, 240 V AC at 60 Hz in the USA is not technically the same as 240 V AC at 50 Hz in other parts of the world. Resistive loads like heaters won't care, but motors and transformers will.
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos
Even more fun is when some numpty gets confused and swaps phase 2 and neutral because they got confused with old and new wiring colours.
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I have experienced this very problem with disastrous results. About 30years ago I was required to re-commission a back-up generator system for Symantec in Dublin, Ireland, where the entire distribution panel had been replaced and upgraded. The generator was a 300kVA, the phases were 3x240mmsq, the neutral was a single 240mmsq and the earth was a 90mmsq. An electrician had taken the generator leads from the old switchover panel and connected them into the new panel and I was called in to do an off-load run prior to full re-commissioning. The generator was somewhat remote from the panel but I could hear it well enough. So as requested I started up the generator from remote start contacts in the panel and ran it for about 10seconds. The generator speed was not as stable as it should have been and suspecting a problem I sent a stop signal. As the generator came to a stop, FLASH! BOOM! from the panel followed by repeated flashes and bangs that seemed to encompass the whole panel until a member of staff tripped the incomer ACB. The electrician had got his colours wrong and the 90mmsq earth had melted and fallen across the three bus bars causing extensive damage. The bars were copper clad aluminium and all had to be replaced.
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I mean to say (sin(x+π/2) + c) - (sin(x-π/2) - c) = sin(x)
they are the same, right?
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It depends on what you mean?
If no current passes through the neutral point, then from an analytical point of view, the 0V point is arbitrary, so both split phase and ordinary phase can be considered to be the same. From a safety perspective, the highest voltage with respect to earth in a split phase system is 120V, but both conductors are above ground potential, compared to single phase which has 230V to earth.
If the neutral point is used, then in all cases, split phase is different to single phase.
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Yes, split phase is a single phase system, you can also think about it as two single-phase supplies in series. The advantage is getting two different voltage options, and possibly safety (with center tap being the earthed potential), but that's all.
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.
This will not change how the C.Tap works. Whatever voltage is on the primary the C.Tap on secondary cuts itself in 1/2.
There's nothing more than 1phase there on the secondary, tapped or not.
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Yes, split phase is a single phase system, you can also think about it as two single-phase supplies in series. The advantage is getting two different voltage options, and possibly safety (with center tap being the earthed potential), but that's all.
That seems to be a bit more confusing. "two single-phase"? Nope, there's only one phase no matter how many coils you put in series on the secondary, or place taps. The 3ph delta or Y could be called "three single-phase supplies", etc.
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.
It's 2-phase split 480V.
Neutral was at 100V wrt ground due to the fault at the transformer. It didn't seem to vary with load, but I don't have any explanation for what nature of fault at the transformer would make it stable at 100V.
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.
It's 2-phase split 480V.
it is only 2 phase if the phases are not a multiple of 180 degrees apart
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.
It's 2-phase split 480V.
it is only 2 phase if the phases are not a multiple of 180 degrees apart
First time I've ever heard that!
- 2 phase: 180º apart
- 3 phase: 120º apart
- 4 phase: 90º apart (logical but may not exist in practice)
Makes perfect sense.
Either way, you can take the hot wires of two adjacent phases and use them as a sqrt(4) or sqrt(3) or sqrt(2) greater sine wave voltage source.
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On a three phase supply with unbalanced loads a break in the neutral connection can cause chaos as one phase will increase in voltage(the less loaded phase) and the other will drop in voltage(the more heavily loaded phase) although the phase to phase voltage will remain as normal and three wire three phase machines will not see a problem. This is most likely the cause of the problem brucehoult experienced.
It's 2-phase split 480V.
it is only 2 phase if the phases are not a multiple of 180 degrees apart
First time I've ever heard that!
- 2 phase: 180º apart
- 3 phase: 120º apart
- 4 phase: 90º apart (logical but may not exist in practice)
Makes perfect sense.
Either way, you can take the hot wires of two adjacent phases and use them as a sqrt(4) or sqrt(3) or sqrt(2) greater sine wave voltage source.
180º is split phase, not 2 phase. 90º apart is 2 phase, like a stepper motor
when you have more than one phase you can generate any other phase angle with a linear combination of the phases
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First time I've ever heard that!
- 2 phase: 180º apart
Mathematically, that would be true. But in conventional electrical engineering, "two phase" is reserved for other cases where the phase angle is not 180°. This is just a convenience of terminology. A centre-tapped transformer is conventionally referred to as "split phase".
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it is only 2 phase if the phases are not a multiple of 180 degrees apart
OK, time for me to set a cat amongst the pigeons here.
Yes, I've heard that stated over and over again.
That is one of the god-damndest stoopidest, most wrong-headed things I've ever heard of!
The supposition that two currents that are 180° apart do not constitute two separate phases, even though they clearly do.
Disclaimer: I never expect to ever win this argument, but I'll argue it anyhow.
This wrong-headed thinking apparently emanates from the electrical industry, who insist on calling 3-phase power "3-phase" and the 180°-apart power "split phase".
They won't admit that it does, in fact, constitute two separate and distinct phases. But somehow, because the phases are mirror images of each other, 180° apart, they won't call them separate phases.
I'm sure if physicists or electronic engineers had their say that split-phase power would be called 2-phase.
What is so fucking special about 180° that its phases don't get called phases?
Yes, I realize that this is yet another dust-up over terminology, but it strikes me as so blindingly, obviously wrong that I just can't hold my tougue.
Stupid sparkies.
How can you tell me that these waves don't constitute two different phases?
[attachimg=1]
[attachimg=2]
And yet if one of them is shifted by 1° then we can call them two phases?
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I'm sure if physicists or electronic engineers had their say that split-phase power would be called 2-phase.
What is so fucking special about 180° that its phases don't get called phases?
2-phase already exists. It has rotation. Split-phase does not.
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2-phase already exists. It has rotation. Split-phase does not.
Please explain; what is meant by "rotation"?
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What is so fucking special about 180° that its phases don't get called phases?
with 180° you cannot make a linear combination of the two and get a get another phase, there's no rotation
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OK, so let's go to basics:
What is the definition of an electrical phase?
(And by "electrical" I do not mean "the electrical industry and common usage among electricians", but the technical definition of wave relationships.)
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Don't we consider a push-pull amplifier to operate on two separate phases, 180° apart?
We speak of "phase splitters", do we not?
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Fuck me, here we go again.. Time to break out the metric rulers to fend him off. Begone, foul beast.
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Fuck me, here we go again.. Time to break out the metric rulers to fend him off. Begone, foul beast.
There's your fucking snobbery on parade again, bub.
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How can you tell me that these waves don't constitute two different phases?
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And yet if one of them is shifted by 1° then we can call them two phases?
In vector algebra, if two vectors are parallel to each other, you do not have a basis for a phase space. You need two vectors that point in different directions to have a basis.
If two vectors have the same direction but differ in the sign of their magnitude, then they are parallel to each other, and are thus not independent. Both vectors are multiples of the same basis vector, and thus you only have a single phase.
Phase angles have to be thought of like a clock. If one arrow points to 12 o'clock, and another arrow points to 6 o'clock, then the only difference between them is the sign (one positive, one negative). You can get an arrow pointing at 6 o'clock if you multiply the 12 o'clock arrow by a negative number. There is no rotation involved, only magnitude.
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How can you tell me that these waves don't constitute two different phases?
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And yet if one of them is shifted by 1° then we can call them two phases?
In vector algebra, if two vectors are parallel to each other, you do not have a basis for a phase space. You need two vectors that point in different directions to have a basis.
If two vectors have the same direction but differ in the sign of their magnitude, then they are parallel to each other, and are thus not independent. Both vectors are multiples of the same basis vector, and thus you only have a single phase.
In my house I have ethernet extenders that plug into power sockets and transmit the data on the power wiring. If I plug all of them into sockets that share the same phase they communicate with each other. If I plug one into a socket that is on the other phase then it can't communicate with the others.
That's "independent".
I'm not in the least bit interested in taking 0.5 of phase 1 and -0.866 of phase 2 in order to make yet another phase. I'm not running industrial machinery or doing mathematics, I'm just plugging in appliances in my house.
I don't agree that two electrical circuits with a common neutral in phase opposition are any less "2 phases" than two electrical circuits with a common neutral that are in quadrature or two electrical circuits with a common neutral that are 120º out of phase with each other.
If you want quadrature then say "two phases in quadrature" don't hijack the entire definition, most especially since 120º and 180º are the angles you actually find in the modern world.
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I don't agree that two electrical circuits with a common neutral in phase opposition are any less "2 phases" than two electrical circuits with a common neutral that are in quadrature or two electrical circuits with a common neutral that are 120º out of phase with each other.
Wait wait wait ...
Are you saying ... that you agree with my argument here? Maybe kinda sorta?
If so, I can die happy.
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In my house I have ethernet extenders that plug into power sockets and transmit the data on the power wiring. If I plug all of them into sockets that share the same phase they communicate with each other. If I plug one into a socket that is on the other phase then it can't communicate with the others.
That's "independent".
I'm not in the least bit interested in taking 0.5 of phase 1 and -0.866 of phase 2 in order to make yet another phase. I'm not running industrial machinery or doing mathematics, I'm just plugging in appliances in my house.
I don't agree that two electrical circuits with a common neutral in phase opposition are any less "2 phases" than two electrical circuits with a common neutral that are in quadrature or two electrical circuits with a common neutral that are 120º out of phase with each other.
If you want quadrature then say "two phases in quadrature" don't hijack the entire definition, most especially since 120º and 180º are the angles you actually find in the modern world.
Language is about communication. If you want to be understood by other people, then you need to use a common language.
For your own private purposes, you are free to use whatever definitions you like. Feel free to disagree with industry norms.
But as far as electrical engineers are concerned, a split phase supply is a single phase supply. Like it or not, that is what the industry has adopted as their terminology.
I'm not an electrical engineer, and I also disagreed with this convention when I learned about it, but as I explained above, there is a reasoning behind the madness. So there is a choice: speak the same language and be understood, or speak a different language and face communication problems.
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For your own private purposes, you are free to use whatever definitions you like. Feel free to disagree with industry norms.
But as far as electrical engineers are concerned, a split phase supply is a single phase supply. Like it or not, that is what the industry has adopted as their terminology.
Care to address the question I posed above about why we refer to two phases in a push-pull amplifier?
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Language is about communication. If you want to be understood by other people, then you need to use a common language.
I note when when I said I had an incident where half my power sockets were at 140V and the other half were at 340V everyone talked about it in terms of two phases.
Which I agree with.
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Care to address the question I posed above about why we refer to two phases in a push-pull amplifier?
Well, for one thing:
I'm not an electrical engineer
So I'm not part of the "we".
But secondly, a push-pull amplifier output stage is a split phase circuit delivering a single phase output. The loudspeaker (load), sees a single phase AC input voltage at its terminals. It doesn't know or care what the amplifier is doing to deliver that.
So no, there are not two phases. There are phase and anti-phase components inside the amplifier circuit, which combine to give the two halves of the single phase output.
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But secondly, a push-pull amplifier output stage is a split phase circuit delivering a single phase output. The loudspeaker (load), sees a single phase AC input voltage at its terminals. It doesn't know or care what the amplifier is doing to deliver that.
So no, there are not two phases. There are phase and anti-phase components inside the amplifier circuit, which combine to give the two halves of the single phase output.
Hopefully not to belabor the point, but I'm referring to the innards of the amp, not its output.
The stage that delivers the two signals 180° apart is commonly referred to as a phase splitter, so how are those (internal) signals not distinct phases?
Or riddle me this: why would we refer to two signals at 0° and 179°, say, as proper phases but not signals at 0° and 180°?
Seems like a distinction without a difference to me.
But what the hell do I know? I ain't an electrical engineer either.
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This whole argument can be solved with a relatively simple math equation
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This whole argument can be solved with a relatively simple math equation
The maths is certainly simple.
And, yes of course, for some purposes it is more useful to have two phases with a significantly non-zero dot product. And for other purposes that doesn't matter at all.
That doesn't make phases with a zero or small dot product not phases.
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Hopefully not to belabor the point, but I'm referring to the innards of the amp, not its output.
The stage that delivers the two signals 180° apart is commonly referred to as a phase splitter, so how are those (internal) signals not distinct phases?
You answered your own question: a phase splitter ties directly into having a split phase system.
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The maths is certainly simple.
And, yes of course, for some purposes it is more useful to have two phases with a significantly non-zero dot product. And for other purposes that doesn't matter at all.
That doesn't make phases with a zero or small dot product not phases.
Well sure, you can call them phases. I would call them phases too. But as far as the industry is concerned it is not a "two phase system".
Don't argue with me, argue with them.
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This whole argument can be solved with a relatively simple math equation
It absolutely can't, because the debate is about words and language, not about math. You can only address the argument using words, and their commonly accepted meanings.
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Well sure, you can call them phases. I would call them phases too.
Thank you; we're in agreement here.
But as far as the industry is concerned it is not a "two phase system".
Don't argue with me, argue with them.
It's a nonsensical distinction on their part.
But as I said, I never expect to win that argument.
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As another poster said "if one can show rotation then there is more than one phase, if not it is single phase", or word to that effect. In amplifier tech to drive a push pull output one needs signals 180degrees apart- one can call this phase splitting, phase inversion or phase shifting, it does not matter. In power engineering the term phase has a somewhat different meaning, the common point between the two is a similar waveform that is or appears to be time shifted.
PS: I had a huge row with an electronics lecturer at college over exact wording. He referred to the phase shifter in an amplifier and I said that it is not a true phase shift but a phase inversion and I suggested a thought experiment where one would put a tiny spike on the waveform to find out has it been time shifted(phase shift) or inverted. He did not like my attitude and his answer was that the waveform would no longer be strictly sinusoidal and therefore phase was irrelevant. I considered this to be bullshit.
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I note when when I said I had an incident where half my power sockets were at 140V and the other half were at 340V everyone talked about it in terms of two phases.
I had an incident where I lost one of the phases to my house - only half of the house had power and the utility company had to bring a special transformer to supply the "missing" phase while they corrected the issue on their end. So yeah, kind of looks like two independent phases :)
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Because single-phase is bipolar, it defines two rotating vectors 180deg apart: motors demonstrate that perfectly, single-phase motors have two set of coils driven 180 deg apart, which push and pull alternatively. There is no concept of split-phase motor because it adds exactly nothing: the same "two phases" 180deg apart can be had by simple polarity reversal from a single supply!
Two-phase motors exist, most notably capacitor-run single-phase motors, stepper motors, and some BLDC fan motors. Distinctive feature is the 90deg phase shift: the bipolarity of the signal itself creates the two more 180deg out-of-phase versions; so a 1-phase motor has 2 poles, 2-phase motor has 4 poles. And yes - in some cases, some people call 2-phase motors 4-phase motors, the same confusion.
That's the practical version of the theory.
Note the difference to DC/DC buck converters: 2-phase buck does have 180, not 90 deg phase shift. This is because the construction is unipolar. In DC/DC buck, 180 deg phase shift doubles the ripple frequency. In bipolar, sinusoidal AC systems - think about full-bridge rectifier - 180 deg out-of-phase separate supply adds exactly nothing (in full bridge diode example, diodes already utilize both polarities).
Split phase AC is like two batteries in series. It offers a center tap for a half-voltage point, nothing more, that's it. Putting 3 AC supplies in series does not make 3-phase power, either.
Transformers with a lot of taps are plentiful. No one in their right mind would call them 5-phase or 9-phase power supplies.
Tapping out intermediate voltages out of AC supply does not generate "phases". The mental trick of choosing one of them as ground/reference level does not change this.
There are people, especially electricians, who use the word "phase" more loosely, kind-of replacement for the word "circuit". They are free to do so. With a split phase (3 wires) entering the house, saying "phase A" and "phase B" is unambiguous, and unnecessary pedantism is tiresome. But here, the OP wants to understand what it really is, and for that, the answer is simple, split-phase is regular single-phase AC with a center tap for half the voltage. That's it.
But the word split-phase exists exactly because it isn't 2-phase system. The word "split" itself suggests that the origin is singular: a single one is being split. 2-phase power distribution did exist. The words are not random, they carry real meanings and history.
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Look: do we not say, without any objection from anybody, that two signals are out of phase with each other if they're 180° apart?
Therefore those signals represent two different phases. Never mind that some people consider that a triviality because one signal is "only" an inversion of the other one, as if 180° is some kind of boogeyman magic number to be avoided.
And the hell with what the hidebound electrical industry considers proper terminology.
I'll still never win this damned argument ...
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What you are saying is correct, no need to win any argument. In power engineering a separate phase refers to a supply that has rotation with respect to the original.
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This discussion led me to search around and, while I agree with the idea that wires carrying electricity at 180° of phase displacement is indeed a two-phase system, I also imagine that the terminology of "phases" for power electricity is intrinsically related to one of its main uses - i.e., to power electrical motors.
A system with 180° of phase displacement will not be able to cause a motor to spin on its own (at least not without the centrifugal switch), thus I imagine they found a need to differentiate that from a two-phase system that is described in the article below
Articles where I got these ideas... :-/O
https://en.wikipedia.org/wiki/Two-phase_electric_power
https://en.wikipedia.org/wiki/Split-phase_electric_power
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What Im curious about is 180 does not divide into 360 by any factor of 3. So how do you get 180* phases from a 3 phase source?
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There are people, especially electricians, who use the word "phase" more loosely, kind-of replacement for the word "circuit". They are free to do so. With a split phase (3 wires) entering the house, saying "phase A" and "phase B" is unambiguous, and unnecessary pedantism is tiresome. But here, the OP wants to understand what it really is, and for that, the answer is simple, split-phase is regular single-phase AC with a center tap for half the voltage. That's it.
Exactly. One of the things I had to "learn" when I started dealing with AC power related measurements is that electricians and linemen use the word "phase" in a much ... looser ... way than electrical engineers.
I'm actually working on a video explaining split phase power distribution, primarily because most of our existing content on power distribution comes out of Europe. A few preliminary slides from the video are attached :)
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There are people, especially electricians, who use the word "phase" more loosely, kind-of replacement for the word "circuit". They are free to do so. With a split phase (3 wires) entering the house, saying "phase A" and "phase B" is unambiguous, and unnecessary pedantism is tiresome. But here, the OP wants to understand what it really is, and for that, the answer is simple, split-phase is regular single-phase AC with a center tap for half the voltage. That's it.
Exactly. One of the things I had to "learn" when I started dealing with AC power related measurements is that electricians and linemen use the word "phase" in a much ... looser ... way than electrical engineers.
I'm actually working on a video explaining split phase power distribution, primarily because most of our existing content on power distribution comes out of Europe. A few preliminary slides from the video are attached :)
So that answers my prior question as well. The 3 phase is double the 120V "end line voltage", so there are 6 120V phases, not 3.
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You cannot directly get a 180 difference from a regular 3 phase system. To get the 180 difference one needs a centre tapped winding on a transformer, that transformer being supplied by one of the three phases.
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By multiple taps on a transformer with both wye and delta windings it is possible to have 12 symmetric phases on the output which if rectified can deliver DC with 3%ripple BEFORE any smoothing caps.
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In a 2-phase system the phases are 90° apart by definition and for pratical reasons (https://en.wikipedia.org/wiki/Two-phase_electric_power).
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What Im curious about is 180 does not divide into 360 by any factor of 3. So how do you get 180* phases from a 3 phase source?
Lets not forget, A rotating mag field cuts coils at different times, this is how phases are made. If a mag field cuts all the coils of the Y at the same time, then you cannot get 3 phases, you have just 1.
We could take a Y, remove one leg, bend one remaining leg so it's 180 from the other, but we only get 2 phases if a mag field cuts each coil at different times.
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I remember watching an animated video trying to explain "Why 3 phases?" It started explaining how the phases were made and how they could be used in balance to provide an effectively "neutral-less" wiring scheme, saving on copper by carrying 3 current carring phases on just 3 conductors.
But it went on to point out that there are many different sets of phases which do this, 6, 12 and many other multiples .
I never do remember the answer as to why most transmission systems stopped at 3.
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I remember watching an animated video trying to explain "Why 3 phases?" It started explaining how the phases were made and how they could be used in balance to provide an effectively "neutral-less" wiring scheme, saving on copper by carrying 3 current carring phases on just 3 conductors.
But it went on to point out that there are many different sets of phases which do this, 6, 12 and many other multiples .
I never do remember the answer as to why most transmission systems stopped at 3.
You answered your own question already.
saving on copper by carrying 3 current carring phases on just 3 conductors.
More phases means more windings, more complicated assemblies, more joints, and more wires to loads.
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I never do remember the answer as to why most transmission systems stopped at 3.
It's the sweet spot of benefits, complexity and cost. In some industrial applications much more phases are used to run large motors. Usually they run their own power plant with a multi-phase generator, or drive the multi-phase generator with a 3-phase motor.
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Please explain; what is meant by "rotation"?
Polyphase systems (Tesla's original polyphase was two phases with one leading the other by 90 degrees) allow you to set up a series of coils that will generate a rotating magnetic field that can power an induction motor. It can also start the motor from a stop. Single or split-phase systems cannot do this and motors powered by this need an auxiliary starting method.
The term "split-phase" is just a handy way of remembering that in practice it has some attributes of a multiphase system (the voltages add up differently depending on which "phases" you select (L1 to L1 = 0V, L1 to L2 = 240V, L1 to N = 120V, etc) but doesn't have other attributes (rotating field, continuous power transmission)
Remember that you can add taps and so forth to get any number of "pseudophases" (new term I just made up) from a transformer but the key is that their magnitudes will always be in sync.
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There are several comments here about two phases "being 180° apart". But how do we know one of them is actually rotated 180° from the other, rather than being reflected or inverted? Reflection and inversion do not involve rotation. It is just an arbitrary choice to say they are phase shifted or inverted. Either is true.
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There are a few ways to create phases. My 3ph drill press has a 1-to-3 VFD.
I just not aware of any big 1ph generator that cuts that up into 3ph for power distribution.
Simple windings separated by 120deg is just easy.
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What Im curious about is 180 does not divide into 360 by any factor of 3. So how do you get 180* phases from a 3 phase source?
You don't of course. Why even ask that question? Why the assumption of 3 phases?
Apples and oranges, man.
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Just a quick note to point out that with regard to my other terminology-related thread about "sodder/soLder", I would never walk into an electrical-supply store and tell the person behind the counter that my home had 2-phase electrical service, because they would give me a strange look: "Do what?".
I recognize that this is simply not the terminology used by that particular industry, for historical reasons, and who am I to go against that? I'm just pointing out the absurdity of it from a technical standpoint, but again, I ain't never gonna win that argument. At least not with that person behind that counter.
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“2-phase” is a reasonable term for Tesla’s original system with 90o difference.
Note that steam locomotives also drive opposite-side wheels in phase quadrature, allowing velocity reversal and starting. There is a classic O Winston Link photograph pair with simultaneous flashes.
There is a subtle difference between “negative” or “inverted” sinusoids and 180o phase difference (think about it), but not relevant to this discussion.
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There is a subtle difference between “negative” or “inverted” sinusoids and 180o phase difference (think about it), but not relevant to this discussion.
I thought about it but couldn't come up with any real difference: seems like a distinction without a difference.
I mean:
[attachimg=1]
[attachimg=2]
What's the "subtle difference"? And how could you possibly know whether one signal was inverted with respect to another versus that signal being shifted 180°?
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What Im curious about is 180 does not divide into 360 by any factor of 3. So how do you get 180* phases from a 3 phase source?
The kms of poles leading cross-country to the transformer at my road gate (and no further ... I am literally the last house on the line, at the boundary of the NorthPower and Top Energy regions) has only two wires. There is only one 11kV phase. So, for whatever reason, they decided to step that down to 480V not 240V.
My half-hour metering actually records each phase separately, plus another field for the controlled hot water heating.
Here's my data from the electricity company for .. let's do today last year :-)
NB Ch1 and Ch2 are the two 240V phases. Ch1 is the one my Pecron power station happens to be plugged into a wall socket on. Ch3 is the controlled hot water heating. My "Free Hour of Power" is set to 9-10 PM. I have a number of things in the house that are not powered by the Pecron e.g. water pump, LED ceiling lighting, stove oven, dishwasher, clothes washer. It was a day with plenty of sun for my 2.64kW of panels.
ICP xxxxxxxxxxxxxxx
Serial xxxxxxxxx
Date 2025-09-28
Flow X
Interval Ch 1 Ch 2 Ch 3 Total
--------------- ------- ------- ------- -------
12:01am-12:30am 0.003 0.005 0.000 0.008
12:31am-1:00am 0.002 0.002 0.000 0.004
1:01am-1:30am 0.002 0.002 0.000 0.004
1:31am-2:00am 0.002 0.003 0.000 0.005
2:01am-2:30am 0.000 0.000 0.000 0.000
2:31am-3:00am 0.000 0.000 0.000 0.000
3:01am-3:30am 0.002 0.005 0.000 0.007
3:31am-4:00am 0.002 0.002 0.000 0.004
4:01am-4:30am 0.002 0.003 0.000 0.005
4:31am-5:00am 0.002 0.002 0.000 0.004
5:01am-5:30am 0.002 0.008 0.000 0.010
5:31am-6:00am 0.002 0.001 0.000 0.003
6:01am-6:30am 0.002 0.003 0.000 0.005
6:31am-7:00am 0.017 0.014 0.000 0.031
7:01am-7:30am 0.011 0.007 0.000 0.018
7:31am-8:00am 0.001 0.003 0.000 0.004
8:01am-8:30am 0.001 0.005 0.000 0.006
8:31am-9:00am 0.001 0.005 0.000 0.006
9:01am-9:30am 0.002 0.003 0.000 0.005
9:31am-10:00am 0.001 0.024 0.000 0.025
10:01am-10:30am 0.001 0.009 0.000 0.010
10:31am-11:00am 0.001 0.004 0.000 0.005
11:01am-11:30am 0.001 0.003 0.000 0.004
11:31am-12:00pm 0.001 0.004 0.000 0.005
12:01pm-12:30pm 0.003 0.007 0.000 0.010
12:31pm-1:00pm 0.001 0.003 0.000 0.004
1:01pm-1:30pm 0.002 0.002 0.000 0.004
1:31pm-2:00pm 0.001 0.003 0.000 0.004
2:01pm-2:30pm 0.001 0.002 0.000 0.003
2:31pm-3:00pm 0.001 0.018 0.000 0.019
3:01pm-3:30pm 0.001 0.002 0.000 0.003
3:31pm-4:00pm 0.001 0.002 0.000 0.003
4:01pm-4:30pm 0.001 0.022 0.000 0.023
4:31pm-5:00pm 0.001 0.002 0.000 0.003
5:01pm-5:30pm 0.001 0.005 0.000 0.006
5:31pm-6:00pm 0.002 0.002 0.000 0.004
6:01pm-6:30pm 0.001 0.006 0.000 0.007
6:31pm-7:00pm 0.001 0.002 0.000 0.003
7:01pm-7:30pm 0.001 0.002 0.000 0.003
7:31pm-8:00pm 0.001 0.005 0.000 0.006
8:01pm-8:30pm 0.001 0.002 0.000 0.003
8:31pm-9:00pm 0.002 0.006 0.000 0.008
9:01pm-9:30pm 1.168 0.007 1.596 2.771
9:31pm-10:00pm 1.081 0.004 1.597 2.682
10:01pm-10:30pm 0.003 0.002 0.010 0.015
10:31pm-11:00pm 0.003 0.002 0.000 0.005
11:01pm-11:31pm 0.002 0.002 0.000 0.004
11:31pm-12:00am 0.002 0.002 0.000 0.004
--------------- ------- ------- ------- -------
Day total 2.343 0.229 3.203 5.775
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There is only one 11kV phase. So, for whatever reason, they decided to step that down to 480V not 240V.
So your 240VAC service is a 480VAC transformer center tapped for neutral (is that grounded?) and your two "phases" are 240VAC, both relative to the center tap/neutral and 180 degrees apart? Not 2 of 3 phases from a 240V 3-PH transformer?
If so, you could have a 480VAC single-phase outlet? I assume this is a smaller installation way out on the end of a long branch, but I'm wondering what the available fault current might be at 480VAC. It sounds sparkely!
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There is a subtle difference between “negative” or “inverted” sinusoids and 180o phase difference (think about it), but not relevant to this discussion.
I thought about it but couldn't come up with any real difference: seems like a distinction without a difference.
I mean:
(Attachment Link)
(Attachment Link)
What's the "subtle difference"? And how could you possibly know whether one signal was inverted with respect to another versus that signal being shifted 180°?
Subtlety: change the frequency and see what happens. As I said, not relevant to this discussion.
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Split phase is just a single phase bipolar or normal/inverted polarity phase. Think of it like unbalanced vs balanced audio. It's the same signal. As others have said it's just a centre-tapped 240V system. rather than having 1 x 240V signal and 1 x Neutral signal you have 2 x 120V signals out of phase.
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There is only one 11kV phase. So, for whatever reason, they decided to step that down to 480V not 240V.
So your 240VAC service is a 480VAC transformer center tapped for neutral (is that grounded?) and your two "phases" are 240VAC, both relative to the center tap/neutral and 180 degrees apart? Not 2 of 3 phases from a 240V 3-PH transformer?
yup
If so, you could have a 480VAC single-phase outlet?
Theoretically possible for sure.
I assume this is a smaller installation way out on the end of a long branch, but I'm wondering what the available fault current might be at 480VAC. It sounds sparkely!
Literally the last two houses on the line, on the boundary of the two northernmost of NZs 29 "electricity distribution networks", which between the two cover the top 255 km of NZ, from the Auckland / Northland province boundary up.
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Brucehoult, just one minor correction to what you said. An 11kV supply is normally 11kV across any two phases with ~6.5kV measured from any phase to ground(earth)/neutral. This is the industry standard and I can't imagine things are different in the antipodes. So your transformer would be fed by two phases, 11kV with 120degrees difference.
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What Im curious about is 180 does not divide into 360 by any factor of 3. So how do you get 180* phases from a 3 phase source?
You don't of course. Why even ask that question? Why the assumption of 3 phases?
Apples and oranges, man.
So. Transmission lines in the US are not 3 phase? Or do those little dustbin sized transformers you all seem to put on poles converting out two 180* phases from the 3?
In the UK the 11kV line is dropped down by minivan sized transformer like 2m cubed. hidden in slack land where houses don't fit. That produces spurs of 3 phase which winds it's way under the roads. One 240V phase brought out and drops a feed into a sequence of houses, another phase does a different sequence of houses and at the end of the cable run there is roughly the same number of house on each phase.
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What Im curious about is 180 does not divide into 360 by any factor of 3. So how do you get 180* phases from a 3 phase source?
You don't of course. Why even ask that question? Why the assumption of 3 phases?
Apples and oranges, man.
So. Transmission lines in the US are not 3 phase? Or do those little dustbin sized transformers you all seem to put on poles converting out two 180* phases from the 3?
I'm no expert in power transmission, so I may be mistaken about part of this.
Some transmission lines here are 3 phase, others are not (just split-phase).
There are only 2 high-voltage lines feeding the transformer on a pole behind where I live, so I'm assuming there must be only 2 "phases" (split phase).
Of course, industrial feeds are all 3-phase. Not sure where the division is between the two; seems like all residential lines are split-phase here.
The utility company must have two completely separate power-distribution networks, one split-phase, the other 3-phase.
I don't see how you could derive 2 180°-apart phases from a 3-phase line (0°-120°-240°), which I think is what you were getting at.
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Brucehoult, just one minor correction to what you said. An 11kV supply is normally 11kV across any two phases with ~6.5kV measured from any phase to ground(earth)/neutral. This is the industry standard and I can't imagine things are different in the antipodes. So your transformer would be fed by two phases, 11kV with 120degrees difference.
There are three conductors further along the road, until the last milking shed. But the poles to my transformer carry only two wires. Yes, I expect they are two phases with 11kV difference and 6.5kV to earth but that's not felt by anything on the secondary side of the transformer which is inherently floating until you earth something.
What I know because I measured it within a few seconds during the fault:
- neutral on all sockets was at 100V wrt the GND pin
- some sockets had 140V phase to neutral
- some sockets had 340V phase to neutral
So I've never measured phase to phase between two different sockets (which would probably need a very long extension cord to a completely different part of the house, not just different sockets in the same room) let alone put both on an oscilloscope, but I'm pretty confident they are 180º apart, and it's not two 120º phases with the transformer using ground-to-phase on the primary side(s).
I do have a very long extension cord I normally use with weed trimmer or pressure washer, and multimeter and 4 chan oscilloscope so I guess I could make the test ... but of course neutral pin is solidly the same as earth pin at all sockets NOW.
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There are only 2 high-voltage lines feeding the transformer on a pole behind where I live, so I'm assuming there must be only 2 "phases" (split phase).
You are getting closer to grokking it! You just applied "2 phases" to 2 wires, which, of course, can only carry one signal. It's the same signal, depending on which of the two wires you take as a reference. Center-tapped transformer scales the amplitude, and adds a reference in the middle.
If you take the voltage between any two wires in 3-phase system (your upstream power distribution eventually) - any two out of the 3 or 4 wires -, you get a single phase, not 2-phase power. 1 phase is 2 wires. 2 phase-power is 3 wires, with double the current flowing in neutral, which is why 3 phase power was invented, which still is 3 wires (optionally, fourth).
High-voltage (high power) distribution is 3-phase everywhere. Yet, a fridge or bulb runs on a single phase everywhere. If you compare US/UK vs. Europe, the point where the single phase branches off the 3-phase distribution, is different. In US/UK whole houses get a large single-phase supply, say 100-200A 240V (US splits that with the center tap, too, which is another orthogonal design choice). In Europe it's more typical that houses get smaller-current 3-phase supplies (say 3 x 35A); apartments have 1-phase supply.
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So. Transmission lines in the US are not 3 phase? Or do those little dustbin sized transformers you all seem to put on poles converting out two 180* phases from the 3?
In the UK the 11kV line is dropped down by minivan sized transformer like 2m cubed. hidden in slack land where houses don't fit. That produces spurs of 3 phase which winds it's way under the roads. One 240V phase brought out and drops a feed into a sequence of houses, another phase does a different sequence of houses and at the end of the cable run there is roughly the same number of house on each phase.
AFAIK, in the US the local distribution is often faned out differently, i.e. one phase/wire (of three, typically 7.2 kV) runs down the poles along a street feeding pole mounted transformers which provide the split-phase to homes. Load distribution across the three phases is done via streets. Based on the number of customers/buildings the poles can carry also two phases or all three. In more densely populated areas you can find pad mounted transformers.
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We still seem to have some confusion here. I strongly recommend the diagrams on post #50, kindly supplied by pdenisowski which explains the US system better than any concoction of words.
PS: That diagram refers to a four wire system which is the system used in Ireland in urban areas and universally used in the UK. In rural areas in Ireland a three wire system is used in which case the transformer primary is fed from two of the phases, ie no neutral wire.
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So. Transmission lines in the US are not 3 phase?
Generation and HV distribution lines are 3-phase. Where the HV distribution goes into what we call a "substation" that HV is stepped down to the medium voltage that is distributed to buildings. This could be 4160V to 13800V or even higher or lower voltages in some cases. In rural and residential areas these medium voltage distribution lines often go a long way (>50 miles in some instances) as only a single phase. Older installations even had one-wire ground-return systems. In the case of my suburban residential area, the main backbone of this distribution system is a 4-wire wye with 13.8KV phase-to-neutral. This is tapped at various points to send one phase at 13.8kV down the various streets and alleys where the pole-pig transformers will step it down to the 240V split-phase that we're talking about.
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In my residential area of Chicago, the pole transformers in the alley behind my house (one per block) are fed by 3000 V (single phase wrt ground) and feed the houses with 240 V split phase. Commonwealth Edison is slowly upgrading the system to 6000 V. At my former employer (in a modern suburban office park), each building had its own transformer (two in my case) fed by high-voltage three phase. Edison supplied the transformers to order for 208 V, 440 V, etc. (line-line) for the customers.
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So. Transmission lines in the US are not 3 phase? Or do those little dustbin sized transformers you all seem to put on poles converting out two 180* phases from the 3?
Yes, transmission and distribution is three phase. But the cylindrical "pole pig" transformers you see on poles are single phase transformers, with a single primary winding and a centre-tapped secondary winding of 120-0-120 V. The primary is connected between one of the distribution phases and ground/neutral, with the transformer can being grounded.
A typical primary voltage is 12.47 kV phase to phase, or 7.2 kV phase to ground.
In the UK the 11kV line is dropped down by minivan sized transformer like 2m cubed. hidden in slack land where houses don't fit. That produces spurs of 3 phase which winds it's way under the roads. One 240V phase brought out and drops a feed into a sequence of houses, another phase does a different sequence of houses and at the end of the cable run there is roughly the same number of house on each phase.
What you are describing happens in towns and urban housing estates.
In rural villages you may still find in the UK something similar to the USA, with transformers sitting on poles, and the 240 V supply wires strung along poles and dropped through the air to the houses. Although there has been a tendency to move this infrastructure underground over time.
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In the case of my suburban residential area, the main backbone of this distribution system is a 4-wire wye with 13.8KV phase-to-neutral. This is tapped at various points to send one phase at 13.8kV down the various streets and alleys where the pole-pig transformers will step it down to the 240V split-phase that we're talking about.
The distribution voltage is most typically measured phase to phase, so a typical 13.8 kV system would be 13.8 kV phase to phase and 8 kV phase to ground.
A classic pole pig has a single primary bushing on top to receive one of the incoming phases, and it drops this to ground through the transformer casing.
Across North America, the most common distribution voltage is 12.47 kV phase to phase and 7.2 kV phase to ground.
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There are only 2 high-voltage lines feeding the transformer on a pole behind where I live, so I'm assuming there must be only 2 "phases" (split phase).
There may be one or two phases (if both wires are on insulators, there are two, often there's only one and the return is ground), they're from a 3-phase system and are 120° apart. You can't tell that without a third reference point (the third phase or ground).
I seem to recall we've seen yours previously: https://www.eevblog.com/forum/chat/(n-american)-line-voltage-120-110-117/msg5852779/#msg5852779 (https://www.eevblog.com/forum/chat/(n-american)-line-voltage-120-110-117/msg5852779/#msg5852779)
This is single-phase using the ground conductor as a return, as far as I can see. I don't see an insulator on the second wire on the pole, I see no second bush on the transformer, and there's only a single HV fuse.
The utility company must have two completely separate power-distribution networks, one split-phase, the other 3-phase.
They do not. They simply tap off one or two phases to feed single phase loads.
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A classic pole pig has a single primary bushing on top to receive one of the incoming phases, and it drops this to ground through the transformer casing.
That seems dangerous using case as the return!! If the case becomes disconnected from ground, the transformer case rises the hot side potential!!
Best
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I'm no expert in power transmission, so I may be mistaken about part of this.
Some transmission lines here are 3 phase, others are not (just split-phase).
There are only 2 high-voltage lines feeding the transformer on a pole behind where I live, so I'm assuming there must be only 2 "phases" (split phase).
No, "split phase" is where you have a center-tapped transformer (two hots and a neutral) on the low voltage side. On the distribution side it is a three phase system. There is no split phase there.
Of course, industrial feeds are all 3-phase. Not sure where the division is between the two; seems like all residential lines are split-phase here.
No, two wires does not mean split phase.
The utility company must have two completely separate power-distribution networks, one split-phase, the other 3-phase.
No, it's all three phase.
I don't see how you could derive 2 180°-apart phases from a 3-phase line (0°-120°-240°), which I think is what you were getting at.
Take any two wires from a three phase supply and you get a single phase. You could take a pair of phase wires and get 12.47 kV phase to phase, or you could take one phase wire to ground and get 7.2 kV phase to ground.
The most common arrangement is that each pole pig takes one distribution phase to ground.
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A classic pole pig has a single primary bushing on top to receive one of the incoming phases, and it drops this to ground through the transformer casing.
That seems dangerous using case as the return!! If the case becomes disconnected from ground, the transformer case rises the hot side potential!!
Best
Typically these will have multiple bonds.
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A classic pole pig has a single primary bushing on top to receive one of the incoming phases, and it drops this to ground through the transformer casing.
That seems dangerous using case as the return!! If the case becomes disconnected from ground, the transformer case rises the hot side potential!!
Best
Maybe so, but that arrangement is rather common. Great care is taken to securely ground all transformer casings, whatever the primary side arrangement. The transformer casing is also the neutral on the secondary side, and this must be grounded to maintain a safe neutral.
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Split phase is just a single phase bipolar or normal/inverted polarity phase. Think of it like unbalanced vs balanced audio. It's the same signal. As others have said it's just a centre-tapped 240V system. rather than having 1 x 240V signal and 1 x Neutral signal you have 2 x 120V signals out of phase.
1ph is 1ph. No shift, no inversion.
Some see a flip because they flip the probes over (using C.tap as the gnd point).
Use one or two o-scopes and probes on a low voltage C.tap xfrmr (12vac w/ C.tap).
(isolated secondary w/ isolated scope inputs)
Probe1------GND
S1-----------C.tap----------S2
Probe2---------GND
Voltage only builds or reduces in one direction (vector) at any given time. Why? Because there's only one mag field vector.
When L1 reaches +6v, L2 is becomes -6v. end-end is 12v differential, end to tap is 6v.
People get tricked when they make C.tap the common for both probes, which make the 1ph look like inversion or 180 shift, it's not.
This setup(view) is deceiving, but is accurate in physics realm.
Probe1------GND
L1-----------C.tap----------L2
GND---------Probe2
Look at it carefully, notice the physical probe is physically flipped over 180deg. ;)
For simple coil xfrmers, unless a mag field cuts coils (or tapped sections of one coil) at different times, then there can only be one phase. You also do not see 3ph on one wire, you must have three 1ph wires. ;)
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Yes, transmission and distribution is three phase. But the cylindrical "pole pig" transformers you see on poles are single phase transformers, with a single primary winding and a centre-tapped secondary winding of 120-0-120 V. The primary is connected between one of the distribution phases and ground/neutral, with the transformer can being grounded.
It would be more accurately stated like +120v --- c.tap --- -120v (VAC rms).
It's a nice sine wave, but from physics it's how the electrons are pushed from one side to the other. As one side goes neg the other side goes pos, charge conservation end-to-end, thus +120 + -120 =0, but the differential (+120 - -120)=240.
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So. Transmission lines in the US are not 3 phase? Or do those little dustbin sized transformers you all seem to put on poles converting out two 180* phases from the 3?
Yes, transmission and distribution is three phase. But the cylindrical "pole pig" transformers you see on poles are single phase transformers, with a single primary winding and a centre-tapped secondary winding of 120-0-120 V. The primary is connected between one of the distribution phases and ground/neutral, with the transformer can being grounded.
A typical primary voltage is 12.47 kV phase to phase, or 7.2 kV phase to ground.
In the UK the 11kV line is dropped down by minivan sized transformer like 2m cubed. hidden in slack land where houses don't fit. That produces spurs of 3 phase which winds it's way under the roads. One 240V phase brought out and drops a feed into a sequence of houses, another phase does a different sequence of houses and at the end of the cable run there is roughly the same number of house on each phase.
What you are describing happens in towns and urban housing estates.
In rural villages you may still find in the UK something similar to the USA, with transformers sitting on poles, and the 240 V supply wires strung along poles and dropped through the air to the houses. Although there has been a tendency to move this infrastructure underground over time.
Plenty of urban areas in the UK still have electricity supplies (and transformers) on poles.
It is just too costly to 'underground' still functional older installations.
There are, of course, arguments for and against undergrounding v aerial supplies.
Our local hospital has an answer I would like to see established whereby the underground services are carried not in backfilled trenches but in concrete channels with sectional concrete lids.
Not only that but each service has a designated place.
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whereby the underground services are carried not in backfilled trenches but in concrete channels with sectional concrete lids.
As was done along the regents canal to bring HV cables into central london.Some sources also claim theres a double bonus as the canal water is used to keep the cables cool
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It would be more accurately stated like +120v --- c.tap --- -120v (VAC rms).
Conceptually it amounts to the right thing, but the notation is a bit flawed. RMS values are strictly magnitudes and cannot be negative. The opposite signs belong to the instantaneous V(t) waveforms (which are 180° out of phase), not to the RMS values.
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It would be more accurately stated like +120v --- c.tap --- -120v (VAC rms).
Conceptually it amounts to the right thing, but the notation is a bit flawed. RMS values are strictly magnitudes and cannot be negative. The opposite signs belong to the instantaneous V(t) waveforms (which are 180° out of phase), not to the RMS values.
Physics is always right, notation can be utterly a royal pita. Engineers usually label things.
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Physics is always right, notation can be utterly a royal pita. Engineers usually label things.
Indeed. But AC is never labeled with +/−. If we write 120-0-120 V AC, then the center zero makes the phasing clear, and no further labeling is needed.
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So just for my own benefit, is it safe to say that this is how split phase is derived from 2 phases of 3-phase power?
[attachimg=1]
(I only drew 3 lines for the 3-phase part. There's no ground conductor there, is there?)
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So just for my own benefit, is it safe to say that this is how split phase is derived from 2 phases of 3-phase power?
(Attachment Link)
(I only drew 3 lines for the 3-phase part. There's no ground conductor there, is there?)
Basically, yes, but the primary (MV) side is an uncommon arrangement, as it requires two line conductors to feed the transformer.
It is more common to ground the low side of the MV primary winding and common it with the LV ground/neutral. (The three MV phases will commonly come from a grounded wye secondary of the supply transformer at the substation, so ground/neutral can be the return from the pole pig back to the substation.)
This arrangement saves money on the pole transformer (it only needs one primary bushing), and on the local distribution network (you only need to take one MV phase around the houses to feed the pole transformers).
You can see this nicely illustrated in this video:
https://www.youtube.com/watch?v=tnRNBw28xOM (https://www.youtube.com/watch?v=tnRNBw28xOM)
In the thumbnail image, you can clearly see the single primary bushing receiving the 7.2 kV supply, and the center-tapped 120-0-120 V secondary bushings, with red and black wires coming from the hot terminals.
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So just for my own benefit, is it safe to say that this is how split phase is derived from 2 phases of 3-phase power?
(Attachment Link)
(I only drew 3 lines for the 3-phase part. There's no ground conductor there, is there?)
Basically, yes, but the primary (MV) side is an uncommon arrangement, as it requires two line conductors to feed the transformer.
It is more common to ground the low side of the MV primary winding and common it with the LV ground/neutral. (The three MV phases will commonly come from a grounded wye secondary of the supply transformer at the substation, so ground/neutral can be the return from the pole pig back to the substation.)
Something like this?
[attachimg=1]
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So just for my own benefit, is it safe to say that this is how split phase is derived from 2 phases of 3-phase power?
(Attachment Link)
(I only drew 3 lines for the 3-phase part. There's no ground conductor there, is there?)
IanB is more detailed. Analog Kid show how it's normally done in Reply #97.
Notice in your pic reply #95, you did not "split" any phase on the primary side. You attached the primary to two phases that are out of phase with each other by 120deg. Only the secondary winding in your pic is "split", or more precisely Center Tapped.
red being the resultant between your primary L1 L2.
(https://i.postimg.cc/nhRjBnG3/differential.png)
Two actual phases 180 shifted from each other
(https://i.postimg.cc/cCr51xhc/differential-180.png)
Two phases (coils) cut at the exact same time, aka "in-phase"
(https://i.postimg.cc/ZYXh92NR/differential-0.png)
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IanB is more detailed. Analog Kid show how it's normally done.
Notice in your pic, you did not "split" any phase on the primary side. You attached the primary to two phases that are out of phase with each other by 120deg. Only the secondary winding in your pic is "split", or more precisely Center Tapped.
red being the resultant between your primary L1 L2.
(https://i.postimg.cc/nhRjBnG3/differential.png)
Two actual phases 180 shifted from each other
(https://i.postimg.cc/cCr51xhc/differential-180.png)
This is completely confusing. What are you even trying to say here?
In both of Analog Kid's diagrams, there is only one phase feeding the primary of the transformer, and only one phase on the secondary. So there are no phase angles, no 120° anywhere.
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So just for my own benefit, is it safe to say that this is how split phase is derived from 2 phases of 3-phase power?
(Attachment Link)
(I only drew 3 lines for the 3-phase part. There's no ground conductor there, is there?)
Basically, yes, but the primary (MV) side is an uncommon arrangement, as it requires two line conductors to feed the transformer.
It is more common to ground the low side of the MV primary winding and common it with the LV ground/neutral. (The three MV phases will commonly come from a grounded wye secondary of the supply transformer at the substation, so ground/neutral can be the return from the pole pig back to the substation.)
Something like this?
(Attachment Link)
Since Randy222 is trying to confuse you, I will respond with a simple: Yes. Basically, that is a common arrangement.
You could even cross out the two unused phases of the three phase supply. If you watch the video I linked, you will see there is only a single phase carried along the top of the distribution poles. Just one wire. Sometimes they don't even bother to carry more than one phase around a local distribution circuit.
There will, however, usually be a neutral return wire back to the substation where you have drawn the ground symbol. You occasionally find "single wire, earth return" circuits, but it is rare as the ground has a higher impedance than a return wire, and it is less efficient to do it that way.
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This is completely confusing. What are you even trying to say here?
In both of Analog Kid's diagrams, there is only one phase feeding the primary of the transformer, and only one phase on the secondary. So there are no phase angles, no 120° anywhere.
Confusing? :-//
Reply #95. Am I not seeing 3 phases with two of them hooked to the primary?
It's actual how it works when there is phase shift between the feed lines. The red line is your volt meter or scope across the primary coil of the transformer when you hook the primary across two phases that are shifted 120deg, or 180deg, or 0deg.
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This is completely confusing. What are you even trying to say here?
In both of Analog Kid's diagrams, there is only one phase feeding the primary of the transformer, and only one phase on the secondary. So there are no phase angles, no 120° anywhere.
Confusing? :-//
Reply #95. Am I not seeing 3 phases with two of them hooked to the primary?
It's actual how it works when there is phase shift between the feed lines. The red line is your volt meter or scope across the primary coil of the transformer when you hook the primary across two phases that are shifted 120deg, or 180deg, or 0deg.
To have a measurable phase angle, you need more than two wires. Since there are only two wires going to the primary, it is a single phase arrangement, and there are no phase angles involved. There is a single phase feeding the primary, and a single (split) phase drawn from the secondary.
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To be clear about this, a phase angle is a difference between two AC voltages, just like a voltage is a difference between two wires. And since a voltage is a difference between two wires, the only way to have a difference between two AC voltages is to have at least three wires so that you can have two voltages to compare.
It doesn't make sense to talk about a phase angle as an absolute quantity.
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This is completely confusing. What are you even trying to say here?
In both of Analog Kid's diagrams, there is only one phase feeding the primary of the transformer, and only one phase on the secondary. So there are no phase angles, no 120° anywhere.
Confusing? :-//
Reply #95. Am I not seeing 3 phases with two of them hooked to the primary?
It's actual how it works when there is phase shift between the feed lines. The red line is your volt meter or scope across the primary coil of the transformer when you hook the primary across two phases that are shifted 120deg, or 180deg, or 0deg.
To have a measurable phase angle, you need more than two wires. Since there are only two wires going to the primary, it is a single phase arrangement, and there are no phase angles involved. There is a single phase feeding the primary, and a single (split) phase drawn from the secondary.
:-//
Last I looked, a 3ph feeder has three wires.
If you want to call Ph1 + Ph2 = one phase, so be it. What you name it does not remove fact the the diagram in #95 is using two phases that are shifted from each other by 120deg. ;) :-+
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So just for my own benefit, is it safe to say that this is how split phase is derived from 2 phases of 3-phase power?
(Attachment Link)
(I only drew 3 lines for the 3-phase part. There's no ground conductor there, is there?)
Basically, yes, but the primary (MV) side is an uncommon arrangement, as it requires two line conductors to feed the transformer.
It is more common to ground the low side of the MV primary winding and common it with the LV ground/neutral. (The three MV phases will commonly come from a grounded wye secondary of the supply transformer at the substation, so ground/neutral can be the return from the pole pig back to the substation.)
Something like this?
Most of our streets have 4-wires (3 phase Wye configuration hot-hot-hot-neutral).
Your diagram appears to show 3-wire delta configuration, your connection between "hot" and ground/neutral will not work on delta configuration....because there's no neutral!!
As an aside, some of our streets have transformers to convert Delta to Wye, as seen in this photo;
[attachimg=1]
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Last I looked, a 3ph feeder has three wires.
If you want to call Ph1 + Ph2 = one phase, so be it. What you name it does not remove fact the the diagram in #95 is using two phases that are shifted from each other by 120deg. ;) :-+
Once again, no.
If you take any pair of wires from a three phase circuit, that gives you one phase. Two wires, one phase.
They are not "shifted from each other" because they carry a single phase AC voltage.
To have a phase angle or phase shift, you need at least a third wire in the circuit.
But two wires alone are just one phase.
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To be clear about this, a phase angle is a difference between two AC voltages, just like a voltage is a difference between two wires. And since a voltage is a difference between two wires, the only way to have a difference between two AC voltages is to have at least three wires so that you can have two voltages to compare.
It doesn't make sense to talk about a phase angle as an absolute quantity.
That sounds a bit confusing.
Is "120deg" not an absolute number in std 3ph generation? :-//
Delta or Y generators, 120deg is it, physically constructed that way.
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To be clear about this, a phase angle is a difference between two AC voltages, just like a voltage is a difference between two wires. And since a voltage is a difference between two wires, the only way to have a difference between two AC voltages is to have at least three wires so that you can have two voltages to compare.
It doesn't make sense to talk about a phase angle as an absolute quantity.
That sounds a bit confusing.
Is "120deg" not an absolute number in std 3ph generation? :-//
Delta or Y generators, 120deg is it, physically constructed that way.
"120deg" is relative, not absolute.
If you can't get your head around the concept, think of GMT time offsets as relative time, and GMT itself as absolute time.
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Your diagram appears to show 3-wire delta configuration, your connection between "hot" and ground/neutral will not work on delta configuration....because there's no neutral!!
Ah, but those electrical engineers are clever fellows! They have thought of that. They only install a transformer with a single wire MV feed when the MV circuit has a wye configuration with a neutral/ground return path back to the substation ;D
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Last I looked, a 3ph feeder has three wires.
If you want to call Ph1 + Ph2 = one phase, so be it. What you name it does not remove fact the the diagram in #95 is using two phases that are shifted from each other by 120deg. ;) :-+
Once again, no.
If you take any pair of wires from a three phase circuit, that gives you one phase. Two wires, one phase.
They are not "shifted from each other" because they carry a single phase AC voltage.
To have a phase angle or phase shift, you need at least a third wire in the circuit.
But two wires alone are just one phase.
Respectfully do not agree with that.
Two independent voltages derived from two separate coils at different times will combine. This does not remove the fact that the two lines are literally phase shifted 120deg from each other.
Work the problem the other way. How could you possibly get higher voltage in the "1ph" than the peak voltage on any of the 2ph lines? Simply not possible with 1ph, the source lines must be phase shifted. :-+
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Your diagram appears to show 3-wire delta configuration, your connection between "hot" and ground/neutral will not work on delta configuration....because there's no neutral!!
Ah, but those electrical engineers are clever fellows! They have thought of that. They only install a transformer with a single wire MV feed when the MV circuit has a wye configuration with a neutral/ground return path back to the substation ;D
Is this common practice? Or is it a state by state affair? Or power grid owner by power grid owner affair?
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Your diagram appears to show 3-wire delta configuration, your connection between "hot" and ground/neutral will not work on delta configuration....because there's no neutral!!
Ah, but those electrical engineers are clever fellows! They have thought of that. They only install a transformer with a single wire MV feed when the MV circuit has a wye configuration with a neutral/ground return path back to the substation ;D
Is this common practice? Or is it a state by state affair? Or power grid owner by power grid owner affair?
I'm not in the industry, I just describe what I see.
I can only suggest you watch this video that I linked above, and see what you see.
Obviously, there will be regional variations, but North America in general has a lot of common practice in power distribution.
https://www.youtube.com/watch?v=tnRNBw28xOM (https://www.youtube.com/watch?v=tnRNBw28xOM)
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To be clear about this, a phase angle is a difference between two AC voltages, just like a voltage is a difference between two wires. And since a voltage is a difference between two wires, the only way to have a difference between two AC voltages is to have at least three wires so that you can have two voltages to compare.
It doesn't make sense to talk about a phase angle as an absolute quantity.
That sounds a bit confusing.
Is "120deg" not an absolute number in std 3ph generation? :-//
Delta or Y generators, 120deg is it, physically constructed that way.
"120deg" is relative, not absolute.
If you can't get your head around the concept, think of GMT time offsets as relative time, and GMT itself as absolute time.
I dunno Andy, last I looked the generator is physically built with output coils that are exactly 120deg apart from each other. I guess you could install a 2nd (but same) generator next to the 1st and rotate the whole thing by 10deg, then I guess we could say the 1st one has phases that are 130deg (or 10deg) relative to the 2nd generator ??
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To be clear about this, a phase angle is a difference between two AC voltages, just like a voltage is a difference between two wires. And since a voltage is a difference between two wires, the only way to have a difference between two AC voltages is to have at least three wires so that you can have two voltages to compare.
It doesn't make sense to talk about a phase angle as an absolute quantity.
That sounds a bit confusing.
Is "120deg" not an absolute number in std 3ph generation? :-//
Delta or Y generators, 120deg is it, physically constructed that way.
"120deg" is relative, not absolute.
If you can't get your head around the concept, think of GMT time offsets as relative time, and GMT itself as absolute time.
I dunno Andy, last I looked the generator is physically built with output coils that are exactly 120deg apart from each other. I guess you could install a 2nd (but same) generator next to the 1st and rotate the whole thing by 10deg, then I guess we could say the 1st one has phases that are 130deg (or 10deg) relative to the 2nd generator ??
Wrong interpretation.
A better interpretation would be wiring up a new coal/nuclear generator plant to the grid. In this case, you need to wire phase A to phase A, phase B to phase B, phase C to phase C, otherwise sparks and fireworks.
But if you have a 3-phase motor at home, you can wire phase A to phase B, phase B to phase C, phase C to phase A. Your motor will run just fine without any problem.
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Wrong interpretation.
A better interpretation would be wiring up a new coal/nuclear generator plant to the grid. In this case, you need to wire phase A to phase A, phase B to phase B, phase C to phase C, otherwise sparks and fireworks.
But if you have a 3-phase motor at home, you can wire phase A to phase B, phase B to phase C, phase C to phase A. Your motor will run just fine without any problem.
:-//
Generator to grid does not remove fact that the 3ph of the generator are fixed (not relative) 120deg shifted from each other. How you sync that onto the grid has nothing to do with fact that the generator output has 3 lines, all 120deg shifted from each other.
So I still not following your relative comment.
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Wrong interpretation.
A better interpretation would be wiring up a new coal/nuclear generator plant to the grid. In this case, you need to wire phase A to phase A, phase B to phase B, phase C to phase C, otherwise sparks and fireworks.
But if you have a 3-phase motor at home, you can wire phase A to phase B, phase B to phase C, phase C to phase A. Your motor will run just fine without any problem.
:-//
Generator to grid does not remove fact that the 3ph of the generator are fixed (not relative) 120deg shifted from each other. How you sync that onto the grid has nothing to do with fact that the generator output has 3 lines, all 120deg shifted from each other.
So I still not following your relative comment.
The relative comment applies to the household motor.
Wiring A to B, B to C, C to A, is relative.
Wiring A to C, B to A, C to B, is relative.
Wiring A to A, B to B, C to C, is absolute.
How about a car cylinder firing order? Is 1-3-4-2 the same as 4-2-1-3? Relatively speaking it is exactly the same, but if you have a newer car with a crankshaft position sensor, then there is an absolute zero degrees of crank rotation, making the two firing orders absolutely different.
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Generator to grid does not remove fact that the 3ph of the generator are fixed (not relative) 120deg shifted from each other. How you sync that onto the grid has nothing to do with fact that the generator output has 3 lines, all 120deg shifted from each other.
So I still not following your relative comment.
The phase rotation is "fixed" in some academic sense, but nobody in the field has an oscilloscope with a long enough probe to reach back to the generator to establish an absolute reference. So all you can do is look at the conductors locally at your disposal, and then all you can do is compare them to find differences between them. If you have two wires to look at, then all you can see is an AC voltage at a given frequency like 60 Hz. That is a single phase. Your oscilloscope will draw a sine wave with a voltage and a frequency, and will set 0° on the trace according to however you set up the triggering.
If you have a third wire to look at, then you can compare it to one of the first two, and then you might be able to see a (relative) phase angle between two voltages. Having three wires will allow you to draw two traces on the oscilloscope.
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How about a car cylinder firing order? Is 1-3-4-2 the same as 4-2-1-3? Relatively speaking it is exactly the same, but if you have a newer car with a crankshaft position sensor, then there is an absolute zero degrees of crank rotation, making the two firing orders absolutely different.
Yet the phase shifting for the cylinders are hard set 180deg, absolute, not relative?
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If you have a third wire to look at, then you can compare it to one of the first two, and then you might be able to see a (relative) phase angle between two voltages. Having three wires will allow you to draw two traces on the oscilloscope.
:-//
Having 3 wires I can get all 3 lines on my 4ch scope, each showing 120deg phase shift.
L1------------L2------------L3
Probe1+ Probe1-
Probe2+ Probe2-
Probe3- Probe3+
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In Ireland on long rural runs we have a three wire system with no neutral connection whatsoever and on the 10kV line the three phases sit nominally ~5.7kV to ground(earth) but not exactly. The advantage of this system is that if a tree falls against one of the wires that wire will go to zero volts wrt ground(earth) and the other two will go to 10kV but importantly rotation is maintained and customers on downstream transformers will not notice any change. Obviously having a tree in contact is not good and to detect this problem we use a transformer with star connected primary and open delta winding on the secondary to measure residual voltage. This fault condition is called a ground(earth) fault.
I hope this digression has not confused anyone.
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Having 3 wires I can get all 3 lines on my 4ch scope, each showing 120deg phase shift.
Relative to each other. Which is the point at hand.
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How about a car cylinder firing order? Is 1-3-4-2 the same as 4-2-1-3? Relatively speaking it is exactly the same, but if you have a newer car with a crankshaft position sensor, then there is an absolute zero degrees of crank rotation, making the two firing orders absolutely different.
a crankshaft sensor cannot tell the difference between the two
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How about a car cylinder firing order? Is 1-3-4-2 the same as 4-2-1-3? Relatively speaking it is exactly the same, but if you have a newer car with a crankshaft position sensor, then there is an absolute zero degrees of crank rotation, making the two firing orders absolutely different.
I don't think the two firing orders are "absolutely different".
The 4-stroke cycle takes up two revolutions of the crankshaft - 720 degrees. A crankshaft position sensor cannot distinguish between the two rotations, which is why cars also have a camshaft position sensor - the camshaft taking 720 crank degrees to make one rotation. In your example, in one crankshaft rotation cylinders 1 then 3 are fired; in the other rotation cylinders 4 then 2 are fired. But the crankshaft starts in exactly the same position for both rotations. So a crankshaft position sensor alone cannot distinguish between the two rotations, meaning there is no "absolute zero" in that sense, and the two firing orders are therefore not "absolutely different".
4-stroke engines have always needed a camshaft position sensor in order to fire the right spark plug at the right time. In pre-electronic times, the distributor acted as a virtual camshaft position sensor, rotating at camshaft speed and being adjusted to open the points at just the right time and sending the spark to the right cylinder.
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Looks like the engine knowledge has surfaced. ;)
And w/ or w/o any sensors, the crank is machined in absolute phasing, two at 0 and two at 180, never gonna change that. If one wished to use a sharpie and put a mark +10deg from 0, and then call the phasing -10 and +170, "relative to the mark", have at it.
There's nothing relative in 3ph phase shift, no matter when or how you look at the 3 lines, 120deg shifting is always there.
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The firing order of the cylinders in an engine is also completely relative.
Basically, you would have ...342134213421342134213... going on forever.
4 comes after 3, 2 comes after 4, 1 comes after 2, 3 comes after 1. These are all relative positions in the firing order.
There is no absolute here, because the crankshaft is circular, and a circle has no beginning and no end. The only thing regulated and determined are relative positions (or angles) such as between valve opening and closing, or when the spark fires, relative to the crankshaft position.
If you identify a crankshaft position and label it 0 degrees, or top dead center, this is just a convenience to help with maintenance and adjustment. It has no intrinsic meaning beyond that. It is exactly the same as choosing a node on a circuit diagram and arbitrarily labeling it as "zero volts" to use as a reference for other voltages. All voltages are relative, but it is convenient to establish a base reference to measure against.
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4-stroke engines have always needed a camshaft position sensor in order to fire the right spark plug at the right time.
Well, not in the case of dual-ended ignition coils that fire two plugs, one of them being a "waste" spark that occurs on the exhaust stroke. :)
But, as IanB points out, firing orders are not just 4 numbers, the whole sequence goes on and on and it doesn't matter where you start. Also there is the issue that for a typical 4-stroke engine the entire cycle is 720 degrees of crankshaft rotation. So I don't think there's too much to be gained in the understanding of single and polyphase power systems by comparing to internal combustion engines.
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6 pages on a simple split-phase question. I am surprised.
Thank God it was not a multiple page datasheet, wonder how many interpretations there are in complex stuff.
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So I don't think there's too much to be gained in the understanding of single and polyphase power systems by comparing to internal combustion engines.
Seems what engineers do. "You" talk about electrical phases and soon enough the conversation jumps to something apparently abstract "relative" to the original topic. In this case, 3ph power jumped to 4cyl engine firing order. :-DD :-+
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Basically, you would have ...34213421342134213421... going on forever.
4 comes after 3, 2 comes after 4, 1 comes after 2, 3 comes after 1. These are all relative positions in the firing order.
4 also fires after 1 and after 2, but later 4 fires before 1 and before 2. Now that's just crazy.
I wonder what the phase shift looks like on the crank for actual positions 1,2,3,4?
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When synchronising a generator to the grid there are three possible connections that are valid. Lets call the grid phases ABC and the generator phases abc. To the grid ABC we can connect with abc or bca or cab it makes no difference as these three(abc, bca, cab) have the same rotation as the grid ABC. The actual process of synchronising requires the frequency, phase and voltage to be matched before connection or trouble will ensue.
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Basically, you would have ...34213421342134213421... going on forever.
4 comes after 3, 2 comes after 4, 1 comes after 2, 3 comes after 1. These are all relative positions in the firing order.
4 also fires after 1 and after 2, but later 4 fires before 1 and before 2. Now that's just crazy.
I wonder what the phase shift looks like on the crank for actual positions 1,2,3,4?
I think at this point you are just being tiresome and misrepresenting everything written in order to be a troll.
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6 pages on a simple split-phase question. I am surprised.
Thank God it was not a multiple page datasheet, wonder how many interpretation there are in complex stuff.
Seems that it's finally pretty simple, main voltage is missing.
And only one coil between phases of delta configured distribution.
Here main voltage between phases is ~400V and phase voltage between phase and ground is ~240V.
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In this case, 3ph power jumped to 4cyl engine firing order. :-DD :-+
Maybe a 3-cylinder two-stroke would be a better case? :)
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In this case, 3ph power jumped to 4cyl engine firing order. :-DD :-+
Maybe a 3-cylinder two-stroke would be a better case? :)
Not sure, need to ask Andy Chee. It could be 1-3-2 or 2-1-3 or 3-2-1, or maybe 1-2-3 or 3-2-1 :-//
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Maybe a 3-cylinder two-stroke would be a better case?
As were discussing phase rotation surely it should be the wankel
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Maybe a 3-cylinder two-stroke would be a better case?
As were discussing phase rotation surely it should be the wankel
Nah. Bringing up a wankel engine and how it operates would just confuse most people. A better example would be the 3 cylinder 2 stroke DKW "3=6" engine or the engine used on the Kawasaki Mach 3 motorcycle.
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When synchronising a generator to the grid there are three possible connections that are valid. Lets call the grid phases ABC and the generator phases abc. To the grid ABC we can connect with abc or bca or cab it makes no difference as these three(abc, bca, cab) have the same rotation as the grid ABC. The actual process of synchronising requires the frequency, phase and voltage to be matched before connection or trouble will ensue.
You have just described relative phase angle.
Absolute phase angle would require alignment along every 360 degrees as well as 120 degrees.
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Dangerous Q and A. risk of fire, shock, death.
Suggest the OP find a licensed electrician in their location.
DO NOT USE A FORUM OR AI FOR MAINS VOLTAGE ELECTRICAL PROBLEMS>
See the professional electricians sites and safety like Mike Holt.
Jon
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Well, not in the case of dual-ended ignition coils that fire two plugs, one of them being a "waste" spark that occurs on the exhaust stroke. :)
I had a 125cc motorbike. Honda CG125. It had an "afterburner". Thats what I called it. A little plug in the exhaust, meant to 'reburn' the exhaust just as it enters the comparitively O2 rich exhaust chamber. Any unburnt fuel well over ignition point just needs a little nudge to burn up. "Clean air system" or some such is the marketing name.
Its also why you see performance cars/race cars etc spitting flames on the overrun. It means they don't have an afterburner, but are dumping lots of unburnt fuel through a insanely hot exhaust so it self ignites. Rally turbos used this effect with thunderous popping and banging anti-lags, using the detonation of the unburnt fuel in the exhaust pipe to drive the turbo on the overurn.
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I would not have thought the small amount of unburnt fuel in the exhaust stream could be ignited but then again this is not my area.
Also would an explosion in the exhaust not drive the turbo backwards?
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4-stroke engines have always needed a camshaft position sensor in order to fire the right spark plug at the right time.
Well, not in the case of dual-ended ignition coils that fire two plugs, one of them being a "waste" spark that occurs on the exhaust stroke. :)
Yes, that's true - it's a workaround, albeit a successful one.
But, as IanB points out, firing orders are not just 4 numbers, the whole sequence goes on and on and it doesn't matter where you start. Also there is the issue that for a typical 4-stroke engine the entire cycle is 720 degrees of crankshaft rotation. So I don't think there's too much to be gained in the understanding of single and polyphase power systems by comparing to internal combustion engines.
I absolutely agree - it's useless as an analogy.
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Also would an explosion in the exhaust not drive the turbo backwards?
Correct, bang bang antilag is adding intentional combustion in the exhaust manifold, before the turbo.
I would not have thought the small amount of unburnt fuel in the exhaust stream could be ignited but then again this is not my area.
These designs intentionally add more fuel and/or drop the spark to leave it completely unburnt and ready to go.
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Not sure, need to ask Andy Chee. It could be 1-3-2 or 2-1-3 or 3-2-1, or maybe 1-2-3 or 3-2-1 :-//
No - this repeats the mistake made when discussing four cylinder engines. There are only two firing orders for a triple: 1-2-3 or 1-3-2. With a four cylinder (using the standard crankshaft configuration) there also only two firing orders: 1-3-4-2 or 1-2-4-3.
The confusion comes from writing these in a straight line. When they are drawn in a circle it all becomes clear.
[attachimg=1, width=800]
Take the left-most diagram: you can start anywhere on the circle, so 1-3-4-2 is the same as 3-4-2-1, 4-2-1-3 and 2-1-3-4. All of those describe the same firing order. The second diagram shows the other commonly used firing order. Note how it is actually the first one reversed.
With triples, assuming a 120-degree crank, the left diagram shows 1-2-3, which is the same as 2-3-1 and 3-1-2. The right-most shows 1-3-2, which is the same as 3-2-1 and 2-1-3. Again, go round the right-most circle anticlockwise and you get the same firing order as the one to its left. Note also that a triple with a 120-degree crank always fires its cylinders in order, from left to right, or from right to left.
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I had a 125cc motorbike. Honda CG125. It had an "afterburner". Thats what I called it. A little plug in the exhaust, meant to 'reburn' the exhaust just as it enters the comparitively O2 rich exhaust chamber. Any unburnt fuel well over ignition point just needs a little nudge to burn up. "Clean air system" or some such is the marketing name.
Yes, an exhaust air injection system. When the burn in the combustion chamber has been incomplete, or when the mixture is rich, unburnt hydrocarbons enter the exhaust system. Air injection introduces more oxygen into the exhaust so that the remaining fuel can be combusted, improving emissions. It's mostly used with a catalytic converter.
Its also why you see performance cars/race cars etc spitting flames on the overrun. It means they don't have an afterburner, but are dumping lots of unburnt fuel through a insanely hot exhaust so it self ignites. Rally turbos used this effect with thunderous popping and banging anti-lags, using the detonation of the unburnt fuel in the exhaust pipe to drive the turbo on the overurn.
Yes: it's a system for keeping the turbo spinning when on the overrun. It's horrendously wasteful, of course. I believe the current implementations add the fuel and air to the intake as usual, but ignite it very late in the cycle so it's still burning when it is pushed into the exhaust by the ascending piston.
EDIT: Sorry, I see now that I've just repeated what @Someone said.
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So I don't think there's too much to be gained in the understanding of single and polyphase power systems by comparing to internal combustion engines.
Axle vibration modeling is easier with electric motor.
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Maybe a 3-cylinder two-stroke would be a better case?
As were discussing phase rotation surely it should be the wankel
two-stroke two cylinder, with a 180 degree crank no matter what direction it turns the sequence is ...1-2-1-2-1-2...,
if the crank is 90 degree the sequence is ..--12--12--12... in one direction, ...--21--21--21--21.. in the other direction
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Not sure, need to ask Andy Chee. It could be 1-3-2 or 2-1-3 or 3-2-1, or maybe 1-2-3 or 3-2-1 :-//
No - this repeats the mistake made when discussing four cylinder engines. There are only two firing orders for a triple: 1-2-3 or 1-3-2. With a four cylinder (using the standard crankshaft configuration) there also only two firing orders: 1-3-4-2 or 1-2-4-3.
The confusion comes from writing these in a straight line. When they are drawn in a circle it all becomes clear.
(Attachment Link)
Take the left-most diagram: you can start anywhere on the circle, so 1-3-4-2 is the same as 3-4-2-1, 4-2-1-3 and 2-1-3-4. All of those describe the same firing order. The second diagram shows the other commonly used firing order. Note how it is actually the first one reversed.
With triples, assuming a 120-degree crank, the left diagram shows 1-2-3, which is the same as 2-3-1 and 3-1-2. The right-most shows 1-3-2, which is the same as 3-2-1 and 2-1-3. Again, go round the right-most circle anticlockwise and you get the same firing order as the one to its left. Note also that a triple with a 120-degree crank always fires its cylinders in order, from left to right, or from right to left.
Does the arrow change if the motor starts with a kickstart that kicks down to front vs down to rear? Or does the OEM just change numbering of the ink in manual?
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Well, not in the case of dual-ended ignition coils that fire two plugs, one of them being a "waste" spark that occurs on the exhaust stroke. :)
I had a 125cc motorbike. Honda CG125. It had an "afterburner". Thats what I called it. A little plug in the exhaust, meant to 'reburn' the exhaust just as it enters the comparitively O2 rich exhaust chamber. Any unburnt fuel well over ignition point just needs a little nudge to burn up. "Clean air system" or some such is the marketing name.
Its also why you see performance cars/race cars etc spitting flames on the overrun. It means they don't have an afterburner, but are dumping lots of unburnt fuel through a insanely hot exhaust so it self ignites. Rally turbos used this effect with thunderous popping and banging anti-lags, using the detonation of the unburnt fuel in the exhaust pipe to drive the turbo on the overurn.
In rockets it's been known for a long time that the high temperature exhaust from a stoichiometric fuel ratio can act as a very powerful oxidizer or fuel. So its a common practice to burn extra fuel to lower the molecular weight of the exhaust without lowering the flame temperature so that the exhaust will have a higher expansion ratio and thus produce most thrust. Prior to emissions controls the same thing was done in automobile engines so the exhaust was also slightly fuel rich. The air injection pumps on the automobile exhaust system and tricks like Paulca is talking about were an early attempt to reduce the (excess) hydro carbon emissions of carbureted automobile engines. Once computer controlled fuel injection replaced carburetors such things were no longer needed
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So I still not following your relative comment.
Not sure if this would help but think about the output of a function generator. A single-output function generator has no phase control. Why? Because altering the phase of the output is meaningless without a second output or reference. What advantage would it hold anyway if you could delay the output by some microseconds? The phase relative to, say, an input reference could be defined, but if the output frequency was different to that reference then it would vary as a function of time.
Another way of thinking about it is the same way we think about voltage. You can't have an absolute voltage because by definition it is a difference in electrical potential between two points. A singular point in of itself has no voltage because both of your probes would be on the same point, measuring a difference of zero. Zero volts. Same goes for phase. You need to measure between different signals (or the same signal at different points in time) to be able to have any measurement of phase shift. Absolute phase is a contradiction of its meaning.
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Also would an explosion in the exhaust not drive the turbo backwards?
Correct, bang bang antilag is adding intentional combustion in the exhaust manifold, before the turbo.
I would not have thought the small amount of unburnt fuel in the exhaust stream could be ignited but then again this is not my area.
These designs intentionally add more fuel and/or drop the spark to leave it completely unburnt and ready to go.
https://youtu.be/rmf0LveXwVk
https://youtu.be/YvgaBWNjrFA
When a rally car is coming, all you hear is "BANG,clatter, clatter ,BANG" and it still half a mile away.
Every time the throttle is lifted, instead of "Dump valving" the over pressure on the turbo, they do the opposite, they inject unburnt fuel into the exhaust and ignite it to detonate and keep pushing high pressure exhaust through the turbo. This allows they to run HUGE turbos with HUGE lag, but as the anti-lag fires constantly the moment they take the foot off the throttle, it's still spinning at full speed on the corner exit ready to apply full power.
On the start line, they hold it on a launch rev point. The anti-lag is running nearly constantly not quite full BANG, but a constnat machine gun of them.
The purpose of the 3-5 seconds like this is to spin the turbo up to full RPM before they leave the line with FULL boost instantly.
EDIT: It should be noted that this practice came under a lot of scrutiny. Ford used a large cylinder in the exhaust system and added valves to it. Then they charged the cylinder up with exhaust and used it to run the turbo. It was promptly banned.
However modern rally cars don't BANG and rattle. They chirp and crackle. Im not sure how they tamed it, possibly by making the detonation much more controlled and engineered rather than something worked out in a shed by a farmer once upon a time.
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I have to wonder how long the turbo blades would stand up to such repetitive pressure spikes. Presumably winning is more important than component longevity, certainly the case with F1.
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If one is interested in turbos, look at Porsche's implementations over the years. They ran the turbos from Rally's to LeMans to Dakar winning in all categories, including F1 (supplied McLaren F1 with TAG engines). Check out the dominations by the 911, 917, 934, 935, 936, 956, 962, and 919 and how the FIA/ACO often enforced rule changes directly targeted against Porsche.
We are especially fond of the 1998 LeMans overall winning 911 GT1 (1 2 finish), the last time a GT type car won outright (Porsche had done this a couple times earlier with 911 variants).
911 GT1 is a variant of the red 911 993 :-+
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Split phase x3, or just 3ph?
(https://i.postimg.cc/dQzSPYKH/3ph.png)
This tech company created a turbo that is also an alternator that you can plug into. Crazy.
(https://i.postimg.cc/nhLm3XPV/cord-on-turbo.jpg)
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That's quite interesting, more details please?
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Indeed, some more info, please. That is an odd looking engine, to me at least.
A turbo would only generate significant power at high revs and gearing would be required to drive an alternator for 60hz although the 60hz could be generated electronically. Offhand without details it does not sound like an efficient method.
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makes my AIs water
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If one is interested in turbos, look at Porsche's implementations over the years. They ran the turbos from Rally's to LeMans to Dakar winning in all categories, including F1 (supplied McLaren F1 with TAG engines). Check out the dominations by the 911, 917, 934, 935, 936, 956, 962, and 919 and how the FIA/ACO often enforced rule changes directly targeted against Porsche.
because Porsche have (very successful) history of spending exorbitant money to show up with a nuclear bomb of car that pushes every grey area of the regulations and killing the race series in the process
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The mechanic is clearly measuring the amount of inverse reactive current going to the unilateral phase detractors, in order to adjust the synchronization of the cardinal grammeters.
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The mechanic is clearly measuring the amount of inverse reactive current going to the unilateral phase detractors, in order to adjust the synchronization of the cardinal grammeters.
So he's running without interocitors?
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The mechanic is clearly measuring the amount of inverse reactive current going to the unilateral phase detractors, in order to adjust the synchronization of the cardinal grammeters.
I don't see any phase detractor meter there, or did I miss it?