Earth Loop Impedance Testing

[JohnW2]

It's commonly known as a "split-phase" in the U.K., and is still found in many rural areas.

Indeed so (although, as you know, the UK Wiring Regulations now call it "180° 2-phase") - but it's not "what it is called" we have been discussing here - rather, the discussion has been about the phase relationship between the two "Ls" with respect to neutral - and I can't really see how anyone can disagree that those L-N potentials are 180° apart.

Kind Regards, John

 

[Mikefromlondon]

That is what I was trying to get at, it is a same phase split into two hence time for negative phase and time for positive phase being same, i.e. no difference, no lag of 10mS if on 50Hz, I know I have problem explaining things, but thanks PBC for clarifying this as I knew it was called something like a split supply or slit phase as you call it.

When you are involved in electronics where we commonly face these in audio signals where phase relationship plays important roll in hearing a clear music in phase, and out of phase can disorientate a listener, where common mode (L & R parts of stereo) signals can be out of phase and can cancel each other and differential signals can add up and so on.

Sorry can't help such discussions, but a split power supplies are commonly used in many modern Amplifiers where they use both + and - rails and a common ground held half way.

 

[PBC_1966]

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°.

voltages are generated as arranged in a 3 phase, 120 degrees apart and at 6.77ms apart as most commonly found in power generation

Or approx. 8.33 & 5.55mS respectively on a 60Hz supply.

 

[PBC_1966]

Indeed so (although, as you know, the UK Wiring Regulations now call it "180° 2-phase") - but it's not "what it is called" we have been discussing here - rather, the discussion has been about the phase relationship between the two "Ls" with respect to neutral - and I can't really see how anyone can disagree that those L-N potentials are 180° apart.

Indeed not - Whatever is being used as the reference point, there's no way to get to 90 degrees as Busbar originally stated. But I suspect he's not seeing this ongiong debate anymore, as his profile says he was last seen on 28-Sep-2015 (unless he's still reading it but not logging in).

Sorry can't help such discussions, but a split power supplies are commonly used in many modern Amplifiers where they use both + and - rails and a common ground held half way.

And in audio amplification, there has long been the transformer with center-tapped secondary used to drive a push-pull output stage, the c.t. being grounded or connected to appropriate grid/base bias so as to obtain signals 180 degrees out of phase with each other to drive each half of the output stage.

 

[JohnW2]

That is what I was trying to get at, it is a same phase split into two hence time for negative phase and time for positive phase being same, i.e. no difference, no lag of 10mS if on 50Hz,

I'm not sure how else to explain. Phase difference (or 'time lag') is measured between one point (e.g. the positive peak) in the waveform of one voltage and the same point (e.g. again the positive peak) in the waveform of the other voltage. One does not look at the phase difference (or 'time lag') between one point in one waveform (e.g. the positive peak) and a different point in the other waveform (e.g. negative peak).

If one voltage reached it's positive peak (relative to neutral) 170° before the other, wouldn't you accept that as a 170° phase difference? If you would, what about 179°, 179.9°, 179.999999° or even 180°??

When you are involved in electronics where we commonly face these in audio signals where phase relationship plays important roll in hearing a clear music in phase, and out of phase can disorientate a listener, where common mode (L & R parts of stereo) signals can be out of phase and can cancel each other and differential signals can add up and so on.

Indeed - and, hypothetically, if you connected two side-by-side identical speakers to the power supply we're discussing, with the "left hand terminal" of each connected to 'neutral' and the other to L1 or L2, then, in a perfect world, you would hear nothing, since the two 180°-out-of-phase signals would result in air pressure changes which would completely cancel. If the voltages were 'in phase' you ought to get a double intensity of the mains hum!

Kind Regards, John

 

[Mikefromlondon]

I agree with your thinking which is from a different angle of course, and you are right, it is like saying is the glass half empty or half full, so it depends how one looks at phases with respect to power, voltage, and a 0 volt reference or Neutral . or between the top peak and the bottom peak, I of course was looking at it from both the top and the bottom peak at the same time, not against a zero reference.

But thanks for taking part in this discussion and thanks to PBC as well for confirming that 90 degree phase shift does not arise in the power lines of a split power supplies, which may be called 2 phase or whatever one chooses to call it, there is no difference in time for the power curve going up and a power curve going down, both occur at the same time with respect to mid point or zero or neutral point, the 90 degree phase difference does not occur as in Busbar's post in that particular scenario.

The confusion lies of course how one looks at it, it is relative to observing point, like when two planes flying in a same path closing on each other, both pilots each pilot accuses the other heading towards him, both are wrong and both are right, all at the same time. (this funny logic!!!!!)

 

[PBC_1966]

There were the old 2-phase 4-wire distribution systems, which had a 90-degree phase difference and were commonly used to feed early electric motors. I believe that New York City for one place maintained such supplies until quite recently (into the 1990's at least).

The other time here that you might see a 90-degree difference is with the 4-wire delta arrangement, if you are talking about the relative phases of the voltages as referenced to the neutral, since phase B voltage is at 90 deg. and phase C at 180 deg. relative to the 0 deg. of phase A.