Just to record a phasor reference

[gar]

120323-1408 EDT

This is just to allow me to record a reference I just found on phasors. It is a rather nice discussion. There is no need for replies.

http://iamechatronics.com/notes/general-engineering/219-ac-electricity-phasor-mathematics

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[iwire]

Please stay on topic, if you can't make your point without jabs at the other members please do not post.

 

[gar]

120326-0855 EDT

iwire:

What does your comment mean? What did I say in post 1 that would result in this comment? And you seem to have replaced your original post #2.

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[pfalcon]

120326-0855 EDT

iwire:

What does your comment mean? What did I say in post 1 that would result in this comment? And you seem to have replaced your original post #2.

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No no gar. He was chastising himself for getting off-topic and taking jabs in post #2 :rotflmao:
Actually I think he's just pre-empting some of the self-righteous comments from the prior thread.
Nice reference gar.

 

[iwire]

What does your comment mean? What did I say in post 1 that would result in this comment?

Nothing, absolutely nothing.

But obviously this is an offshoot of the phase thread and I am just reminding all of the rules.

It was not specifically directed at you.

And you seem to have replaced your original post #2.

Yes, the first post in case you did not see it was posted when I closed this thread for a cooling off period.


Now, please back to the OPs topic.

 

[rattus]

Just to clear up some incorrect notions:

Just to clear up some incorrect notions:

RMS voltages and currents are indeed scalar quantities, but hang a phase angle on them and we have static phasors which are used in the solution of steady state problems and the construction of phasor diagrams, e.g., the delta and wye diagrams. They certainly do not rotate.

Impedances are also considered to be phasors.

Phasors may be represented graphically, and problems may be solved graphically, but they are supported by the underlying complex math. A mathematical solution is more precise than a graphical solution and is therefore preferred.

Phasors may be added, subtracted, divided, and multiplied, but care must be taken when multiplying voltage and current lest one think power has a phase angle.

 

[pfalcon]

RMS voltages and currents are indeed scalar quantities, but hang a phase angle on them and we have static phasors which are used in the solution of steady state problems and the construction of phasor diagrams, e.g., the delta and wye diagrams. They certainly do not rotate.
Impedances are also considered to be phasors.
Phasors may be represented graphically, and problems may be solved graphically, but they are supported by the underlying complex math.
... (pulled below) ...
Phasors may be added, subtracted, divided, and multiplied, but care must be taken when multiplying voltage and current lest one think power has a phase angle.

Rearrangement mine. None of the above has ever been questioned.

A mathematical solution is more precise than a graphical solution and is therefore preferred.

This isn't correct. The graphical solution is only limited by your means of measurement.

 

[rattus]

This isn't correct. The graphical solution is only limited by your means of measurement.

I can get 10 digits of precision on my calculator. I would guess that you can get maybe three digits with a drafting machine and an engineer's scale.

But no matter, this is a side issue which I will not pursue any further.

 

[ggunn]

I can get 10 digits of precision on my calculator. I would guess that you can get maybe three digits with a drafting machine and an engineer's scale.

But of what use are those 10 digits of precision? If (for example) your input data has only three significant figures, any beyond that in your output data are just random numbers.

 

[gar]

120326-1049 EDT

I have always used the word "phasor" to mean what rattus defines as "static phasor". In a PM I essentially asked him to define what he meant by "static" vs "rotating" phasors. He did this and I suggest now that he repeat the definitions here in his own style.

I have not made a major study, only a cusory look, at the origin of vectors and phasors in AC circuits. The use of some form of vectors instead of instantaneous equations for the analysis of steady state AC signals is attributed to Charles Steinmetz of (from Wikipedia)

Shortly after arriving in the U.S., Steinmetz went to work for Rudolf Eickemeyer in Yonkers, New York, and published in the field of magnetic hysteresis. Eickemeyer's firm developed transformers for use in the transmission of electrical power among many other mechanical and electrical devices. In 1893 Eickemeyer's company, along with all of his patents and designs, was bought by the newly formed General Electric Company.

Of general interest is
http://www.schenectadyhistory.net/wordpress/wp-content/uploads/2010/07/Steinmetz-Papers.pdf but does not contain information I am looking for.

Another interesting reference is (but hard to read)
http://archive.org/stream/revolvingvectors00pattrich/revolvingvectors00pattrich_djvu.txt

I have not found a good history reference at this point that is directly available on the Internet.

Have to leave for a while.

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[rattus]

But of what use are those 10 digits of precision? If (for example) your input data has only three significant figures, any beyond that in your output data are just random numbers.

Of course. I was merely stating the relative precision of the graphical vs the mathematical.

 

[rattus]

120326-1049 EDT

I have always used the word "phasor" to mean what rattus defines as "static phasor". In a PM I essentially asked him to define what he meant by "static" vs "rotating" phasors. He did this and I suggest now that he repeat the definitions here in his own style.

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Be glad to.

The rotating phasor as used in "crank diagrams" is helpful in understanding how an alternator generates sinusoidal waves. It is a useful learning tool. It is of the form:

v(t) =Vpeak[cos(wt + phi) + jsin(wt + phi)]

where phi is the phase angle or phase constant and Vpeak is a magnitude, always positive.

The static phasor lets 't' = 0 thereby eliminating wt from the equation. It is of the form:

V = Vrms[cos(phi) + jsin(phi)]

where phi is the phase angle and Vrms is a magnitude, always positive.

We use static phasors in steady state calculations and phasor diagrams.

The term 'phasor' has been around for over 50 years now, yet some persist in calling them vectors which is not technically correct. Vectors have a magnitude and direction in space. Phasors have a magnitude and phase angle which translates to time, plus the rules for handling them are a bit different.

 

[iceworm]

---

Of course. I was merely stating the relative precision of the graphical vs the mathematical.

Adding to ggunn's post:
I'm not real clear on this relative percision. In particular if one multiplies two 3 digit numbers, each with an accuracy of +1 or -1 on the third significant digit, the answer is still no better than 3 significant digits with an accuracy of +1 or -1 on the third significant digit. 10 digits of resolution on ones calculator does not change this.


ice

 

[ggunn]

Of course. I was merely stating the relative precision of the graphical vs the mathematical.

Which is my point, of course. That mathematically "precise" result isn't precision at all when the data input is imprecise. If there are only three significant figures in the least precise input term, then the output can be no more precise than that. A slide rule would be just as precise as a computer in that case.

 

[rattus]

Back to the OP's question:

Back to the OP's question:

The OP asked why we call residential service single phase when two phases are present in a split phase service.

The answer is quite simple: Although there are technically two phases present, they are derived from a single phase transformer, therefore it is single phase. These two phases are important in a full wave rectifier and also in creating 240Vrms from two 120Vrms sources.

We got hung up because some could not see that the voltages on L1 and L2, when defined relative to the neutral, are real, but they are real because they are defined relative to the neutral. Let's call them V1n and V2n. They are inverses of each other and separated by PI radians.

Others claimed that V1n and V2n were 'in phase' and 'of the same phase' although they carry different phase constants.

Still others claimed that an inversion does not create a phase shift which is irrelevant to most if not all power problems.

So, let's get on with a civil discussion.

 

[rattus]

Which is my point, of course. That mathematically "precise" result isn't precision at all when the data input is imprecise. If there are only three significant figures in the least precise input term, then the output can be no more precise than that. A slide rule would be just as precise as a computer in that case.

If you wish to discuss precision, I suggest you start a new thread.

 

[gar]

120326-1510 EDT

There are some broad basic concepts that are important to consider. These are what need to be discussed.

A historical perspective can bring to light why certain concepts were developed.

Prior to 1850 little was known about electricity. Quite possibly the first electric industry was the telegraph, 1844. See http://memory.loc.gov/ammem/sfbmhtml/sfbmtelessay.html

How were voltage, current, and resistance defined and measured in 1850? Do some searching.

What instruments were used to measure current in 1879?

When did Weston improve the d'Arsonval meter?

How were AC circuits analyzed in 1890?

What was Steinmetz's profound concept circa 1892?

Note: I do not believe Steinmetz created the word "phasor" to describe his concept. One book I have with a 1951 copyright (Bailey and Gault) does not use phasor but uses vector, while Stout in his book copyright 1952 is indicating that phasor is coming into use instead of vector.

From http://zrno.fsb.hr/katedra/download/materijali/966.pdf

Charles Proteus Steinmetz
CHARLES STEINMETZ WAS BORN IN Breslau, Germany in 1865 and emigrated to
the United States in 1889. In 1892, he began working for the General Electric
Company in Schenectady, New York, where he stayed until his death in 1923,
and it was there that his work revolutionized ac circuit analysis. Prior to his time,
this analysis had to be carried out using calculus, a difficult and time-consuming
process. By 1893, however, Steinmetz had reduced the very complex alternatingcurrent
theory to, in his words, ?a simple problem in algebra.? The key concept
in this simplification was the phasor?a representation based on complex numbers.
By representing voltages and currents as phasors, Steinmetz was able to
define a quantity called impedance and then use it to determine voltage and current
magnitude and phase relationships in one algebraic operation.
Steinmetz wrote the seminal textbook on ac analysis based on his method,
but at the time he introduced it he was practically the only person who understood
it. Now, however, it is common knowledge and one of the basic tools of
the electrical engineer and technologist. In this chapter, we learn the method and
illustrate its application to the solution of basic ac circuit problems.
In addition to his work for GE, Charles Steinmetz was a professor of electrical
engineering (1902?1913) and electrophysics (1913?1923) at Union University
(now Union College) in Schenectady.

More references:
http://en.wikipedia.org/wiki/Phasor_(sine_waves)

From Wikipedia
http://en.wikipedia.org/wiki/Phasor_measurement_unit

In 1893, Charles Proteus Steinmetz presented a paper on simplified mathematical description of the waveforms of alternating electricity. Steinmetz called his representation a phasor.[3]

Did he call it a phasor or a vector. I do not know at this time. Parking is too difficult at the U of M Library so I do not plan to go looking there at the moment.

^ Charles Proteus Steinmetz (1893). "Complex Quantities and Their Use in Electrical Engineering". Proceedings of the International Electrical Congress, Chicago (Chicago, Illinois 1893 conference of the AIEE: American Institute of Electrical Engineers Proceedings): 33?74.

One book reference I found on Google seems to imply that Steinmetz described his concept as a rotating line (probably meaning some form of vector). This means it is really necessary to look at the original 1893 publication.

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[pfalcon]

... Although there are technically two phases (2) present, they are derived from a single phase (1) transformer, therefore it is single phase (1). These two phases (2) are important in a full wave rectifier and also in creating 240Vrms from two 120Vrms sources.

See, this is where I keep bringing up that the word phase is an overloaded word. You make one paragraph and swap the definition twice. (1) relates to the OP question. (2) relates to field practice. Both are valid definitions but are mutually incompatible during this discussion. They cannot both be proven using the same set of tools or arguments.

We got hung up because some could not see that the voltages on L1 and L2, when defined relative to the neutral, are real, but they are real because they are defined relative to the neutral. Let's call them V1n and V2n. They are inverses of each other and separated by PI radians.

Aside from the statement being non sequitor that they're real because you defined them that way: I don't believe anyone has claimed there aren't voltages at L1 and L2 usable by definition (2) or that they're anything other than real. But, as above, this is related to field practice and not the OP question.

Others claimed that V1n and V2n were 'in phase' and 'of the same phase' although they carry different phase constants.

Again, they only carry different phase constants for field practice (definition 2) which doesn't relate to the OP question.

Still others claimed that an inversion does not create a phase shift which is irrelevant to most if not all power problems.

Here we're close to the heart. but if on this you continue to revert to (2) then we'll never make progress. I'll start with a separate post from this one.

So, let's get on with a civil discussion.

Amen

 

[iceworm]

[

The OP asked why we call residential service single phase when two phases are present in a split phase service. ...

So, let's get on with a civil discussion.

iwire -
I had understood the 2500+ post, dumptruck load was to be reopened. Is this it? From gar's opening post, I didn't think it was.

ice

 

[iwire]

[

iwire -
I had understood the 2500+ post, dumptruck load was to be reopened. Is this it? From gar's opening post, I didn't think it was.

ice

As I said in my post when I closed that thread, I planed to reopen in 24 hours unless the other mods had other opinions. Right now it is still up in the air.

For us to put it back would mean one of us would have to edit out the comments. I can tell you that is not an easy task as the jabs and insults are usually interwoven with legitimate comments and no matter how the edits are done everyone will be upset.