I must admit that the first statement quoted is remarkably confusing. Irish and English are completely different languages.
Earth Loop Impedance Testing
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Could you be mistaken since you said " I believe 90 degrees out of phase"
They could be out of phase with respect to Neutral with no difference in time or degrees, hence 0 degrees difference, you might be getting 240v between the two "hot" wires L1 & L2, but with respect to Neutral each one gives you 120v and Neutral also connected to ground potential.
This is a configuration you can get from a center tapped transformer, with the centre tap being your neutral, and grounded. Your two hot wires therefore can have opposite phases so L1 could be +120v with respect to CT (centre tap) AND L2 being -120v with respect CT that being your Neutral connected to ground or earth, giving you a choice to use either 120v when connecting between neutral and L1 or Neutral and L2, and if you wanted 240v equipment connected you would then use L1 and L2 and not use neutral . I agree it would give an impression that they were 90degrees out of phase.
This is easily achievable from a sub station transformer wound to give + & - 120v plus a neutral this 3 wires plus local earthing.
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Sorry John yes in a way one would say that they are 180 degrees out of phase with one another, but when speaking in terms of power, as in a 3 phase supply, each phase is 120 degrees apart and time shifted, i.e. they do not all happen at the same time) but in this above example the phases are opposite and yes can be referred to as 180 degrees apart, but there is no time difference.
As for voltage one phase would be going in a positive direction, and the other in a negative going direction both at the same time with no time lag and with respect to Center Tap. (Which is also your Neutral and connected to earth) Both peak at the same time in two different directions providing 240v.
(unlike in our mains supply, the two phases are 180 degrees apart but also phase shifted by 180 degrees, that is they do not peak in different directions at the same time)
Hence using three wires, one neutral and two hot wires or lives, one can have a choice of 120v or 240v if and when required. *(not sure if this is called a split supply)
As for voltage one phase would be going in a positive direction, and the other in a negative going direction both at the same time with no time lag and with respect to Center Tap. (Which is also your Neutral and connected to earth) Both peak at the same time in two different directions providing 240v.
(unlike in our mains supply, the two phases are 180 degrees apart but also phase shifted by 180 degrees, that is they do not peak in different directions at the same time)
Hence using three wires, one neutral and two hot wires or lives, one can have a choice of 120v or 240v if and when required. *(not sure if this is called a split supply)
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... but there surely is a "time difference". Just as with a 3-phase supply, the 'positive peaks' of the three phases are about 6.67 msec apart (i.e. 20 msec/3, aka 120°), with the arrangement you are talking about the 'positive peaks' are 10 msec apart (20 msec/2, aka 180°).
The difficulty, which is the reason why many people do not like calling the arrangement '2-phase' is that, since there are only two 'phases' to look at (forgetting the centre-tap/'neutral'), one cannot really talk about a 'phase difference' between the two phase conductors (just as one can't for a single-phase supply).
Kind Regards, John
I think we are both looking at it from different angle, hence i don't see what you are seeing and you don't see what I am looking at. And I agree it is highly confusing for the other, so may be it is best if we can meet and see it from one angle! (That was just a gesture) no seriously though you know how it is, you are quite right just as I am since I am looking at it from my angle, and you are from yours, I see no time difference, yet it also seems that there has to be time difference.
If you take a single phase AC power (voltage/current) of any frequency, and feed this sign wave into a primary windings of a transformer that has two separate secondary windings. You connect the two windings in series such that the end of the first set of winding is connected to the start of the second. (connected in series) and this junction/point is referred to as a Center Tap, it is then connect or labelled as "Neutral" and the start of first set of secondary winding can be labelled as L1, and the end of the second set of winding can be labelled as L2.
Suppose you had arranged the transformer such that a 240 volt ac into its Primary windings would give you two Secondary outputs of 120v each, such that the total voltage between L1 and L2 would add up to 120+120 = 240v
But, this is where my angle comes into, if you were to look from this joint between the two windings, and we labelled it as Neutral, and connected to ground, we can then measure the peak at L1 as -ve 120v at exactly the same time as the L2 +ve 120v, hence no time lag and no shift in phase, the two polarities are in the same time frame but of opposite polarities and follow the same phase time relationship as the input phase time shift.
I can understand why you can't see that, may be it is more to do with electronics rather than power generation, but both principles can be applied to one another.
In another example if you connect 2 x 1.5v cells in series, and have the center tapped, then with respect to center tap, one battery will give you a -1.5v and the other will give you a +1.5v, both at the same time with no phase shift or time lag. and if you measure the L1 of one battery with the L2 of the other, the net total voltage will be 3v.
but if this is going to cause more confusion let us leave it at that.
If you take a single phase AC power (voltage/current) of any frequency, and feed this sign wave into a primary windings of a transformer that has two separate secondary windings. You connect the two windings in series such that the end of the first set of winding is connected to the start of the second. (connected in series) and this junction/point is referred to as a Center Tap, it is then connect or labelled as "Neutral" and the start of first set of secondary winding can be labelled as L1, and the end of the second set of winding can be labelled as L2.
Suppose you had arranged the transformer such that a 240 volt ac into its Primary windings would give you two Secondary outputs of 120v each, such that the total voltage between L1 and L2 would add up to 120+120 = 240v
But, this is where my angle comes into, if you were to look from this joint between the two windings, and we labelled it as Neutral, and connected to ground, we can then measure the peak at L1 as -ve 120v at exactly the same time as the L2 +ve 120v, hence no time lag and no shift in phase, the two polarities are in the same time frame but of opposite polarities and follow the same phase time relationship as the input phase time shift.
I can understand why you can't see that, may be it is more to do with electronics rather than power generation, but both principles can be applied to one another.
In another example if you connect 2 x 1.5v cells in series, and have the center tapped, then with respect to center tap, one battery will give you a -1.5v and the other will give you a +1.5v, both at the same time with no phase shift or time lag. and if you measure the L1 of one battery with the L2 of the other, the net total voltage will be 3v.
but if this is going to cause more confusion let us leave it at that.
... but you're comparing chalk and cheese. The +120v peak in L1 occurs 10 msec before/after the +120V peak in L2 - that's a time lag (or 'lead') of 10 msec or, if you prefer, a phase difference of 180°.
Your 1.5V cell analogy is not really relevant since, being DC, the concept of 'time lag' cannot arise. As for "phase shift", the only equivalent with DC is polarity (which can only be 'same' or 'opposite'), and the ends of your two cells with respect to the centre point would have 'opposite polarities', which is the DC equivalent of a 180° phase shift.
Kind Regards, John
What you must remember a Transformer is not a like a Generator, in a Generator phases are generated at different times as it is spun, and as the poles go past each other whilst rotating, hence voltages are generated as arranged in a 3 phase, 120 degrees apart and at 6.77ms apart as most commonly found in power generation. However, In a transformer you have a single phase input that follows incoming Sine Wave, so the secondary output will also follow the phase relationship of the input thereby making no difference in time, but only in polarity, this is the cause of misleading.
My battery cell analogy was to demonstrate if you were to freeze time frame at a particular phase of the input, say the Live was going up in heading a positive direction and had reached peak, the wave was frozen as if it stood there for ages, and not changing, so you would be looking at that particular time frame. (time frozen)
I thinkl we will both have to take this up in a pub over a pint! Bring your sketch pad with you and I will bring my pen!
My battery cell analogy was to demonstrate if you were to freeze time frame at a particular phase of the input, say the Live was going up in heading a positive direction and had reached peak, the wave was frozen as if it stood there for ages, and not changing, so you would be looking at that particular time frame. (time frozen)
I thinkl we will both have to take this up in a pub over a pint! Bring your sketch pad with you and I will bring my pen!
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and now someone will come and say you can't freeze time! so now I wish i hadn't started! LOL
I think you're making it unnecessarily complicated by considering where the voltage comes from. Think of a "black box" (which might contain a generator, a transformer powered by some source, or whatever) about which all you know is that it has three output terminals, labelled L1, neutral and L2. Regardless of what is in that box, with respect to neutral, the voltages on L1 and L2 will be 180 degrees out of phase ... with respect to 'neutral', when L1 is +120V, L2 will be -120V, when L1 is +40V, L2 will be -40v etc, and the time interval between when L1 is +120V and L2 is +120V will be 10 msec (assuming 50Hz!).
Kind Regards, John
You will have to buy me beers now!
I reckon I've now said everything I have to say, so maybe I can escape that!
Kind Regards, John
Nope you can't escape, until I have my beers to accept your view! I take bribery for sure!
It's commonly known as a "split-phase" in the U.K., and is still found in many rural areas. Here in the U.S. it's just called single-phase 3-wire and is the standard supply for residential and light commercial use, the main difference being that here all homes take the full 3-wire service so as to have 120 & 240V available whereas most U.K. homes on a 240/480V system have only a 2-wire connection for 240V.
And I don't think that's a bad analogy, since single-phase 3-wire AC is really just the AC equivalent of the 3-wire DC distribution which was installed in some cities in the early days.
John and I have debated the whole 1-phase vs. 2-phase issue extensively before, after the IET decided quite out of the blue to go against over a century of the system being recognized as single-phase and decree that henceforth BS7671 would refer to it as a 2-phase 3-wire system.
Yes, if you measure the voltages at each end of the transformer relative to the center tap, they are indeed 180 degrees out of phase with each other. But for power distribution and use it's the current which provides that power, and adding the center tap and extending it to the installation as a neutral doesn't add any different phases of current, hence why it's always been recognized as single phase.