Why is residential wiring known as single phase?

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rbalex

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But they are not in phase.
What aren't in phase? They may not be synchronized, but based on the definition I provided in 1214, the transformer secondary voltages definitely are in phase. I suspect if you did the Fourier analysis, the phase characteristics of the fundamental frequencies of Ia and Ib would be too; but they don’t need to be for the transformer secondary voltages to be.

Phase isn't defined by the load characteristics; at most, the load characteristics may be described by the system voltage characteristics. That is we, don't call three-phase systems "three-phase" because they drive three-phase motors, we call motors "three-phase" because they are driven by a three-phase system. Otherwise, every load characteristic would properly demand a new system description.
 
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rattus

Senior Member
They're not.
Were it so, the circuit in post #1004 wouldn't work.
Think about it.
Why are Ia and Ib not in phase?

Perhaps the problem is that Bes labeled the xfrmr with RMS voltages with no phase information. If he had labeled them with 120Vrms @ 0 and 120Vrms @ 180, there should be no argument. Or he could have placed polarity dots on the two halves of the secondary. In any case though, the voltages must be separated by 180 degrees to achieve full wave rectification.
 

rattus

Senior Member
Perhaps the problem is that Bes labeled the xfrmr with RMS voltages with no phase information. If he had labeled them with 120Vrms @ 0 and 120Vrms @ 180, there should be no argument. Or he could have placed polarity dots on the two halves of the secondary. In any case though, the voltages must be separated by 180 degrees to achieve full wave rectification.

Or, since it is a center tapped winding with the CT as common, one should know the two voltages are separated by 180 degrees.
 

mivey

Senior Member
And how are these two quotes related in your mind?
I said I used "in phase" like our industry does. You responded that it was technically incorrect, industry or not, and did not apply to a technical discussion. I replied that the sources were mainly used in the technical arena. In fact, most are used in teaching and how much more technical does it get than that?

Now, how about commenting on the one with two sources you attached your comment to.
Again, in response to your talking about using one voltage in two ways at the same time.

Try and keep up with your own strings in the thread.

I'm suggesting you expand the experiment.
Weren't my experiments. These were in the 1860's.

LoL, but a resounding NO. AC travels inside the copper to a depth determined by frequency. I get to deal with a lot of induction hardeners. If the current and power didn't flow through the metal they wouldn't heat or harden. It takes frequencies well above what we're using to become a wave guide.
Just more electrical theory you don't understand. If I thought there were a lot of others who did not understand how energy is transmitted, it might be worth me drafting an in-depth explanation in a separate thread. But no pearls tonight.

Nah, Va to Vb is like connecting any of the three phase wye legs to neutral. Same phase, different ends of the coil.
What would you call two ungrounded conductors on the primary side being shorted?
 

mivey

Senior Member
And with that response, I will again withdraw from the "oscilloscope jungle" and allow those of you with, "Have oscilloscope, will probe" tattooed somewhere on your anatomy to continue with your guerilla war, ambushing each other; each content in the firm belief that your position is unassailable by anyone who "oscilloscope challenged"; that there is no mathematics to be applied beyond arithmetic and the only valid definition is how you apply it in your particular branch of the industry - although you can't even seem to agree on that.

One would think you would at least give some deference to:

From IEEE Std 100 The IEEE Standard Dictionary of Electrical and Electronic Terms:
After all, it did come from your branch of the industry. (?(IM) [120]? indicates the definition was extracted from IEEE Std 120-1989. IEEE Master Test Guide for Electrical Measurements in Power Circuits.) I'm sure at least some of you may even have it on your bookshelf.
Yeah, I have it and the definition was not in there. The discussion about measuring phase angle said you could use a digital or analog method. I have an analog phase angle meter and it measures the phase angle between two waveforms in one degree increments from 0? to 360?: no resetting or "resolving" down to a "fundamental" phase angle.

Also, in IEEE 120, you might note that figure 2-6 has the secondaries in reverse polarity and the text reads:
A simple transductor consists of two single-phase transformers, with the direct current to be measured passing through the primary windings in series, while the secondaries are connected through the meter to a source of ac voltage. The secondary windings are connected in series and in opposite phase as shown in Fig 2-6.
 

jim dungar

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In the circuit, which you kindly posted in #1194, the current never flows from N towards B.
I know the diode blocks it, I said in the 'direction of', it would have made it if the waveform had not been interrupted.


No disagreement with that.
But using Rattus' voltage directions and polarity dots, they are not in-phase. If the current is flowing out of X1 and X3 at the same time then V12 and V34 should be in-phase at the same time correct?
 

rbalex

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Yeah, I have it and the definition was not in there...:
I apologize, the bracketed [120] in IEEE Std. 100-1996 definition refers to the IEEE Instrumentation and Measurement Society. I should have reread the Std. 100 introductory material ? it?s been a while.

Nevertheless the IEEE Std. 100 definition as cited is accurate and I believe both it and the source is still authoritative with respect to Instrumentation and Measurement.
 

rattus

Senior Member
I know the diode blocks it, I said in the 'direction of', it would have made it if the waveform had not been interrupted.

But using Rattus' voltage directions and polarity dots, they are not in-phase. If the current is flowing out of X1 and X3 at the same time then V12 and V34 should be in-phase at the same time correct?

Jim, when current flows in T1, there is zero current in T2. Then after a half period, the situation is reversed.

V12 and V34 are always in phase. V12 and V43 are in antiphase. I think that is what Bes is saying to you.
 

gar

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120222-2254 EST

Assuming an original voltage source is a sine wave. This source feeds either one or two ideal transformers. If it is a single transformer, then it has two identical secondaries. If it is two transformers, then the two transformers are identical.

By my definition of "in-phase" in this circuit you can parallel two secondaries with no appreciable circulating current resulting. Any other phase relationship will cause circulating current. In particular a 180 degree phase shift, inversion if you want to call it that, will cause a maximum and very large circulating current. Any non-"in-phase" relationship is an "out-of-phase" condition.

Can you connect the two outer ends of a center tapped transformer together and have essentially no circulating current, or do you get big sparks? No sparks and the coils are "in-phase". No meters, no scopes, just a simple experiment.

The sources I have previously referenced would support my use of "in-phase".

Tried to quickly go back to some other references provided by others. Did not get very far.

Post 1084 on p 28 does not define "in-phase".

Post #13 on p 1 is an incorrect description. Two voltages differing by 180 degrees produce a large voltage difference, not 0 volts. A zero phase difference and equal magnitudes would produce a zero voltage difference.

Two coherent monochromatic light waves at a point and with a phase displacement of 0 degrees produce a bright spot or band, displaced by 180 degrees and the result is a dark band. Interferometry. How a diffraction grating works.

.
 

Gac66610

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Location
Kansas
jumping from page to page i see a lot of "in phase"' "0 volt". "high volt", all fine arguments. could the answer to original question, (why is it called single phase), be answered a little more simply
i have been asked that question by a builder who may or may not care but i cant go to him and say half of whats posted here, suppose i could print all let him read it:),
i'm just a simple electrician not looking to get anyone upset so what i say please take with a grain of salt (or sugar)
i mainly work resi. i have work commercial, never seen 2 phase (after this thread) hope i never do
could we simply say that resi single phase only has one(1) way to get 240v reading between L1 & L2 and thats where single phase comes from
2 phase like i stated never seen it hope never to run across it
then we could say three(3) phase we have three(3) different ways to obtain a 240v reading L1 to L2, L2 to L3, and L3 to L1, and thats where 3 phase comes in

or just continue thread for another 1000 posts:thumbsup:
 

Fulthrotl

~Autocorrect is My Worst Enema.~
or just continue thread for another 1000 posts:thumbsup:

ahem.... should i paste this? oh, why not......

http://en.wikipedia.org/wiki/Two-phase_electric_power

and for those of you who are so twizzled at this point that clicking
on the link is more than you can bear..... here is the text....

Two-phase electric power
From Wikipedia, the free encyclopedia

Two-phase electrical power was an early 20th century polyphase alternating current
electric power distribution system. Two circuits were used, with voltage phases
differing by 90 degrees. Usually circuits used four wires, two for each phase.

Less frequently, three wires were used, with a common wire with a larger-diameter
conductor. Some early two-phase generators had two complete rotor and field
assemblies, with windings physically offset by 90 electrical degrees to provide
two-phase power. The generators at Niagara Falls installed in 1895 were the
largest generators in the world at the time and were two-phase machines.

The advantage of two-phase electrical power was that it allowed for simple,
self-starting electric motors. In the early days of electrical engineering, it
was easier to analyze and design two-phase systems where the phases were
completely separated.[2] It was not until the invention of the method of
symmetrical components in 1918 that polyphase power systems had a
convenient mathematical tool for describing unbalanced load cases.

The revolving magnetic field produced with a two-phase system allowed
electric motors to provide torque from zero motor speed, which was not
possible with a single-phase induction motor (without extra starting means).
Induction motors designed for two-phase operation use the same winding
configuration as capacitor start single-phase motors.

Three-phase electric power requires less conductor mass for the same voltage
and overall amount of power, compared with a two-phase four-wire circuit of
the same carrying capacity.[3] It has replaced two-phase power for commercial
distribution of electrical energy, but two-phase circuits are still found in certain
control systems. Power transfer in a three-phase system with balanced loads is
constant, whereas it pulsates at twice the line frequency in single-phase systems.
These power pulsations tend to cause increased mechanical noise in transformer
and motor laminations due to magnestriction and torsional vibration in generator
and motor drive shafts.

Two-phase circuits typically use two separate pairs of current-carrying conductors.
Alternatively, three wires may be used, but the common conductor carries the
vector sum of the phase currents, which requires a larger conductor. Three-phase
can share conductors so that the three phases can be carried on three conductors
of the same size. In electrical power distribution, a requirement of only three
conductors, rather than four, represented a considerable distribution-wire cost
savings due to the expense of conductors and installation.

Two-phase power can be derived from a three-phase source using two transformers
in a Scott connection: One transformer primary is connected across two phases of the supply.
The second transformer is connected to a center-tap of the first transformer, and is
wound for 86.6% of the phase-to-phase voltage on the three-phase system. The secondaries
of the transformers will have two phases 90 degrees apart in time, and a balanced two-phase
load will be evenly balanced over the three supply phases.

Three-wire, 120/240 volt single phase power used in the United States and Canada is
sometimes incorrectly called "two-phase". The proper term is split phase or 3-wire single-phase.
The two live outputs of a 3-wire single phase transformer secondary winding are properly called "legs".


true two phase 4 wire systems are like a two cylinder engine, with the power pulses 90 degrees
apart.

think harley.
 

Besoeker

Senior Member
Location
UK
What aren't in phase?
Me - Why are Ia and Ib not in phase?
You - They don't need to be.

Sounds like you're agreeing that they are not in phase. If they are not in phase, they are out of phase. If they are out of phase, they are not the same phase. If they are not the same phase, they are different phases. If they are different phases, there must be more than one phase. If there is more than one phase the system cannot reasonably be described as single phase.
QED.
 

Besoeker

Senior Member
Location
UK
I know the diode blocks it, I said in the 'direction of', it would have made it if the waveform had not been interrupted.
"Flowing in the direction of" is what you actually posted.
The point of the simple example was to show that there is a positive half cycle of current from A to N and another positive half cycle of current from B to N at a different time.
That would happen with or without diodes in the circuit.
If they happen at a different time, they are not in phase. They thus cannot be the same phase. So there is more than one (single) phase.
 
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