Why is residential wiring known as single phase?

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rbalex

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No apology required.



All the tags in there that show up when composing a response make that very difficult to read in plain English. So I've just picked out one point.

There is no secondary delta connection. I should have thought that perfectly evident.
The arrangement shows six voltages. i have given the expression for each. All different.
That's why it's hexaphase.
Hopefully to make it a bit clearer:

If you limit your described system to the star connections, assuming a common t0, all six voltage functions may still be written validly in terms reduced to ([ωt + φ0]), ([ωt + φ0]+ 120?) and ([ωt + φ0]+ 240?) or their equivalent inverses.

What genuinely creates "hexiphase" is the secondary line to line voltages that are also valid; whether you use them or not.

Depending on the actual secondary connection, (DyN1 or DyN11) the additional three phases would be ([ωt + φ0]+30?), ([ωt + φ0]+ 150?) and ([ωt + φ0]+ 270?) or ([ωt + φ0]-30?), ([ωt + φ0]+ 90?) and ([ωt + φ0]+ 210?) or their equivalent inverses.
 
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rattus

Senior Member
However, V2n = -120Vrms(sin(wt)) is a legitimate substitution and both functions are in terms of "wt."

NO IT IS NOT! The two expressions in a trig identity must be equal in every respect including their phase constants.

-sin(wt) is nothing more than the equivalent of sin(wt + PI). You cannot ignore the minus sign. You would fail trig if you did. That is an improper application of trig identities.

Phase must be extracted from the POSITIVE sine function. It is undocumented nonsense to claim that a sinusoid can have two phases! Show me some documentation that validates this nonsense.

Whatever silly claims you make about identities, I choose not to use identities. I think any knowledgeable engineer would do the same.
 
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rbalex

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NO IT IS NOT! The two expressions in a trig identity must be equal in every respect including their phase constants.

-sin(wt) is nothing more than the equivalent of sin(wt + PI). You cannot ignore the minus sign. You would fail trig if you did. That is an improper application of trig identities.

Phase must be extracted from the POSITIVE sine function. It is undocumented nonsense to claim that a sinusoid can have two phases! Show me some documentation that validates this nonsense.

Whatever silly claims you make about identities, I choose not to use identities. I think any knowledgeable engineer would do the same.
You're embarrassing yourself.
 

rattus

Senior Member
The reason why I keep pointing this out as "the pot calling the kettle black" is because you originally transformed (aka "twisted" to use your words) the original expression to introduce the phase constant, but then demand others provide some sort of reference to "untwist" your original transformation.

In other words, your argument is that it is OK for you to do it, but for someone else to either undo it, or never do it in the first place, then they must provide a reference to support the operation. That's a double-sided argument.

If you can perform this operation without reference, then others can undo it without reference. If you do it with reference, then the same reference permits it to be undone too.

Just a straight forward answer Rick. No lecture needed.
 

mivey

Senior Member
We all know that our industry has common usage that is known to be in error--current direction versus electron direction to be the most obvious. I am not arguing conventions or names. I am arguing the technical specifics because this is a technical discussion.
Then just focus on what you agree is a phase shift. These are the results of a physical change, not a time delay.

I am still unclear about why you refer to these as "physical phase shifts". I have never heard it expressed that way, so I am unsure why this is considered "physical". From my perspective, nothing "physical" has changed, so I am unclear why this word appears in the description.

It is not like an audio phase shift:

It really is a simple thing. Don't allow the focus on time shifting to cause you to lose sight of how we create phase shifts by physical shifts. It might be hard to focus on a physical shift if you have recently been absorbed in a project dealing with phase shifts in audio signals because the majority of the time there it does mean a time delay.

In the electric world, the majority of the phase shifts we see are physical in nature. The signals have their peaks occurring at different times, but that does not mean the signals are time-shifted versions of each other, especially if we look back at the signal beginning. The shift is the result of a physical difference, not sending a signal through a delay box. We do have propagation delays that can show up when tying long transmission lines together. That delay is a true time shift. But we are talking about the shifts in equipment like we have in the transformers.

The phase shift in a three-phase generator is not caused by a time shift. The fact that the windings are physically shifted relative to each other gives us the phase shift. An artifact caused by something impacting the source to the generator (a tree stuck in the river/lake dam intake, for example) will show up on all three voltages at the same time. The artifacts will be at different locations relative to the peaks because the peaks have a physical phase shift.

In these type cases it is a physical shift, not a time shift, causing the phase shift. It is the same type phase shift I showed in my generator example by physically rotating the generator shaft. It is the same type shift I showed in my open-wye example by taking voltages from different terminals and different directions in a transformer. It is the same type shift I showed in my open-wye graphic with the anomalies.



Phase shifting transformers:

I mentioned phase shifting transformers used in metering as another example of a physical shift causing a phase shift. To give a rough illustration of the physics, look at a high-leg delta. Take a voltage from the high-leg to the center-tap neutral point. Now instead of having a single center-tap point, replace that with a wiper that will allow you to access any point on the center-tap winding.

As we slide the end point of the voltage up and down the winding, we shift the phase of that voltage relative to the others. That is basically how a phase-shifting transformer works in three-phase metering. It is a physical shifting of the voltage that causes the phase shift, not a time shift. Source anomalies will not be time displaced unless you use relative time references (different zero crossings, etc.). In other metering equipment, we actually do use a time delay from impedance circuits to give us the phase shift we need.



Time shift:

In one case, we can have a time shift (delay circuits, propagation delays, etc) that changes the time relationship between one wave and a reference wave. This will also affect the physical relationship between this shifted wave and a reference wave. A source side anomaly will appear at different points in time but at the same place on the waves. If we change the reference time for each wave to be the positive slope zero crossing of each wave, the anomalies will appear at the same relative points in time.

This is not the type of phase shift we are usually concerned with in transformers and generators.



Physical shift:

In another case, we can have a physical shift (taking voltages from different terminals and different directions, etc.) that changes the physical relationship between one wave and a reference wave. This will also affect the timing relationship between this shifted wave and a reference wave. A source side anomaly will appear at the same point in time but at different places on the waves. If we change the reference time for the positive slope zero crossing of each wave to be the positive slope zero crossing of the reference wave, the anomalies will appear at different relative points in time.

This is the type of phase shift we usually are concerned with in transformers and generators.



It is a two-sided coin:

The relative nature of the time reference for the waves makes the time shift and the physical shift two sides of the same coin. Not the same side, but the same coin. It is a two-sided coin because we can look at the same time as a reference for all waves, or we can look at the same physical wave characteristic as a reference for each wave.

Again, there is a relative relationship between the physical shift and the time shift. We can look back at the beginning of signal creation to see which side of the coin we are looking at. Whatever the side, it is still a phase-shift coin. We normally don't care what side of the coin we are looking at because we deal with steady-state conditions.



It might not agree with the terminology you prefer, but it is the way "phase shift" is used as related to shifts in transformers. In addition to "phase shift", you will also see the terms "phase displacement" and "phase difference" and other similar terms used both together and separately.

Do you understand what I mean now?
 

pfalcon

Senior Member
Location
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... I mentioned phase shifting transformers used in metering as another example of a physical shift causing a phase shift. To give a rough illustration of the physics, look at a high-leg delta. Take a voltage from the high-leg to the center-tap neutral point. Now instead of having a single center-tap point, replace that with a wiper that will allow you to access any point on the center-tap winding.

As we slide the end point of the voltage up and down the winding, we shift the phase of that voltage relative to the others. That is basically how a phase-shifting transformer works in three-phase metering. It is a physical shifting of the voltage that causes the phase shift, not a time shift. Source anomalies will not be time displaced unless you use relative time references (different zero crossings, etc.). In other metering equipment, we actually do use a time delay from impedance circuits to give us the phase shift we need. ... Do you understand what I mean now?

Yes, as usual, you authoritatively spout nonsense.

Voltages:
By physical reality, at t0 and every 1/2 cycle they're all 0V across the coil. At 1/4 cycle one end will have risen to +120V and the other will have fallen to -120V. At 3/4 cycle they'll reverse. In truth, from one end of the secondary to the other we have a voltage gradient. The proportion of the distance between any two probes compared to the overall length will yield a proportional voltage reading. Hence the 120/240V system is also called an AC Voltage Divider.

So, to arguments about phases:
Compelled as we are to have labels in order to speak about things, it's common practice to refer to the wave form generated by the voltage as a phase. Having no better word, and through common usage, therefore it is. Further, A and B generate phases with opposite polarity as referenced from N. It's important to note that these voltage phases have nothing to do with why the system is called single phase. There is still only one induction field present which is the phase that gives single phase it's name. But the English language is renowned for overloading words with multiple meanings.

Phase 1: The phase generated by the induction field that gives single-phase it's name.
Phase 2: The individual voltage readings that can be measured.
Phase 3: The individual current readings that can be measured.

Phase is an overloaded word just as the word duck is (duck beneath, also the water fowl). Therefore depending on which usage the poster is discussing may generate 1, 2, 4, 6, or infinite phases. All are legitimate answers depending on the usage in play. But only one usage gives the system it's name.

The phase of the voltage never changes just because you move your reference point (Phase 1); but the measured phase of the voltage does change (Phase 2).
 

Rick Christopherson

Senior Member
Do you understand what I mean now?
No I do not. What you (I believe) are calling "physical" phase shifts are the antithesis of actually being physical, and are actually the mathematical shifts I am referring to. You are also focusing a little too heavily on the word "Delay" as a description of a phase shift. Not that this is incorrect, but I believe it is causing you to think of phase shifts in the wrong perspective.

I don't want to sidetrack the discussion, but let me at least address your example of a 3-phase generator. In this particular example, you stated that there isn't a time delay, but there actually is. Moreover, it is actually the easiest case for seeing that there is a time delay.

Even though the diesel engine's crankshaft begins rotating at t0, the rotor's field winding does not reach each of the stator windings at the same instant. There is in fact a physical delay as the stator makes its revolution past each of the three stator windings. The delay isn't at the rotation start point of the crankshaft, but when the rotor reaches each winding.

Given this information above, would you mind re-explaining when you can have a phase shift that is not also a time shift? Unless I missed something, the only example you have been able to give is when you have an inversion that mathematically equates to a time shift. (And not to harp on it, but I still don't understand what you mean by "physical" phase shift. Switching test leads is not physically changing the system that is being examined.)
 

rattus

Senior Member
Homework Problem:

Plot the functions, sin(wt) and -sin(wt) and determine the phase of each.

Solution:

The plots are inverses of each other, so I would think that do not carry the same phase.

Certainly wt is the phase of the first, but am not so sure of the second.

Flash of genius: Apply a trig identity to get the answer I want even if it may be wrong.

-sin(wt) = sin(wt + PI)

The answers are: wt and (wt + PI)

But that looks right not wrong to me. Phases differ by PI the difference in phases? Just like the plots, separated by PI?

Naw, couldn't be! Too easy.

BTW, I couldn't find anything to support this move, just made it up myself.
 

__dan

Senior Member
dan, forget the transformers.

I have a basement full of transformers, surplus takeouts and some I bought at liquidation. I have these fuel heater units from when boilers burned heavy tar fuel. The secondary voltage is stepped down so low it would be bolted directly to a malleable iron nipple to heat the nipple (the fuel line). I have antiques, stacks of old neon sign transformers, old welders with big carbon shoes that ride right up and down the output winding. Ideally, the stuff would be for a lab, to play with.

You are asking for a reference, well, the transformer is a reference. You want to ignore that reference and substitute in a menagerie of voltage sources that do have phase shift concerns.

I read a little from the thread in post #6 from 2006. I was surprised how much had been said already, including the 'forget the transformer and add (subtract) the phasors'.

There was a good analogue from that thread. From the passenger side of the car look at the front tire as it rolls forward. The tire rotates in the clockwise direction. Now look at the front tire from the driver's side as the car rolls forward and the tire rotates in the counterclockwsie direction. There is no change in the underlying physical reality. What changes is your point of view. And if you add the phasors for each tire from both measurements, they sum to zero. However, the movement of the car is not zero.

The rules of logic specify that when arriving at a defective conclusion, it is time to check your premises for defects.

A lot of electricians have no problems bolting wires on a transformer but are afraid to throw the switch for the first time. That's a good sign, knowing what you do not know. Then they get in the car and drive unconcerned that their front tires are rotating in exactly opposite directions and mathematically, the car is not moving. Are you presenting a problem that the electrician needs to be concerned about or is the subtract when I am adding not in alignment with the industry standards.

Is there a conveyance of understanding or does the paradigm present its own internal contradictions and defects.
 
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pfalcon

Senior Member
Location
Indiana
Homework Problem:
Plot the functions, sin(wt) and -sin(wt) and determine the phase of each.
Solution:
The plots are inverses of each other, so I would think that do not carry the same phase.
Certainly wt is the phase of the first, but am not so sure of the second.
Flash of genius: Apply a trig identity to get the answer I want even if it may be wrong.
-sin(wt) = sin(wt + PI)
The answers are: wt and (wt + PI)
But that looks right not wrong to me. Phases differ by PI the difference in phases? Just like the plots, separated by PI?
Naw, couldn't be! Too easy.
BTW, I couldn't find anything to support this move, just made it up myself.

...
Phase 1: The phase generated by the induction field that gives single-phase it's name.
Phase 2: The individual voltage readings that can be measured.
Phase 3: The individual current readings that can be measured.

Phase is an overloaded word just as the word duck is (duck beneath, also the water fowl). Therefore depending on which usage the poster is discussing may generate 1, 2, 4, 6, or infinite phases. All are legitimate answers depending on the usage in play. But only one usage gives the system it's name.

Except, wasn't it your definition that neglected polarity? In which case |-sin(wt)| = |sin(wt+Phi)|; I think that definition is buried some 100's of posts back.
But then again, the OP was about the system phase label, not the individual voltages.
 

gar

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EE
120306-1712 EST

A classic way of defining simple harmonic motion is to use a disk of radius R and rotated at a uniform angular velocity. Pick a point on the radius of the disk and project the motion of that point to the Y axis. The result is a sinusoidal variation with angular rotation of the disk.

Add a second point on the radius displaced by some non-zero or non N*2*Pi angle, and a second, but separated simple harmonic motion is generated.

These two motions have identical shapes when plotted vs the angle of the shaft, but are displaced from each other by a "phase difference". That "phase difference" exists at zero velocity as well. Time does not have to be part of the phase difference definition.


A different question for each of the responders.
Do you favor RPN calculators like HP, or so called algebraic like TI?

.
 

rattus

Senior Member
120306-1712 EST

A classic way of defining simple harmonic motion is to use a disk of radius R and rotated at a uniform angular velocity. Pick a point on the radius of the disk and project the motion of that point to the Y axis. The result is a sinusoidal variation with angular rotation of the disk.

Add a second point on the radius displaced by some non-zero or non N*2*Pi angle, and a second, but separated simple harmonic motion is generated.

These two motions have identical shapes when plotted vs the angle of the shaft, but are displaced from each other by a "phase difference". That "phase difference" exists at zero velocity as well. Time does not have to be part of the phase difference definition.


A different question for each of the responders.
Do you favor RPN calculators like HP, or so called algebraic like TI?

.

You mean like fixed (static) phasors?

RPN of course.
 

__dan

Senior Member
Whut'd he say? dan that is.

I said the paradigm you present has an internal contradiction or defect. The sum of the phasor measurements = zero. However, the sum measured at the actual is not zero. Your paradigm must contain a defective premise.

RPN only. I have a hard time using a calculator with an equals sign and no stack. Hp 48g and have one of these:

http://www.hpmuseum.org/hp34.htm
 

rattus

Senior Member
I said the paradigm you present has an internal contradiction or defect. The sum of the phasor measurements = zero. However, the sum measured at the actual is not zero. Your paradigm must contain a defective premise.

RPN only. I have a hard time using a calculator with an equals sign and no stack. Hp 48g and have one of these:

http://www.hpmuseum.org/hp34.htm

Maybe your paradigm should subtract instead of add??
 

Besoeker

Senior Member
Location
UK
Hopefully to make it a bit clearer:
To you or to me?

If you limit your described system to the star connections, assuming a common t0, all six voltage functions may still be written validly in terms reduced to ([ωt + φ0]), ([ωt + φ0]+ 120?) and ([ωt + φ0]+ 240?) or their equivalent inverses.
I provided expressions for all six voltages.


What genuinely creates "hexiphase" is the secondary line to line voltages that are also valid; whether you use them or not.
What genuinely makes it hexaphase is that there are six phases.
 

__dan

Senior Member
Maybe your paradigm should subtract instead of add??

I have done it both ways, adding windings in series and adding voltage, adding windings that are reversed turn direction and subtracting voltage.

For the OP's inquiry, the subject transformer has windings wound in the same direction, on the same core. Adding the windings adds the voltage, which is what is observed.

Why you insist I should subtract, I have no clue.
 

rattus

Senior Member
I have done it both ways, adding windings in series and adding voltage, adding windings that are reversed turn direction and subtracting voltage.

For the OP's inquiry, the subject transformer has windings wound in the same direction, on the same core. Adding the windings adds the voltage, which is what is observed.

Why you insist I should subtract, I have no clue.

Well, I thought you were familiar with complex numbers and phasors. You are finding the DIFFERENCE between two voltages, therefore you subtract.

How do you obtain 208V from any two legs of a 120V wye? Try it with 120V @ 0 and 120V @ -120; what do you get?
 
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