Is impedance a phasor?

[rbalex]

Having been a member of ten national and one international technical committees, including five IEEE, one of the reasons I prefer their definitions is their Standards, including the definitions, go through a fairly extensive vetting process. While there isn't always universal agreement for most US Standards (IEEE, NFPA, API), there is a very strong consensus, since it takes a minimum 2/3 majority to pass. The international standards (IEC) are virtually unanimous - almost everyone, including the janitor, seems to have veto power.

The current IEC/IEEE standard I?m working on has already taken over five years of deliberation. The ?final? ballot was circulated three days ago. Hopefully no one will raise a comment this time.

After national/international consensus document defintions, I prefer standard textbooks. Most of them also have a fairly solid vetting process. Definitions gleened from the Internet are more problematic. This is not to say they are wrong, but they are rarely subject to peer review. My biggest mistake in the other thread was not starting off withthe IEEE defintion. Historically, as happened there also, people fixate on the note rather than the defintion. I should have just ridden with it.

 

[iceworm]

Don't have IEEE 100 and your excerpt from it came through all garbled. ...

I'm not going to send it to you. Since you are discussing precise technical definitions I'd say it is worth heading to the library and reading selected sections.

... Whatever I think our discussion should be limited to steady state analysis of AC circuits, ...

okay. I'll likely bow out though. Especially if the discussion is about how to draw the arrows to represent a house service.

... I repeat, there is no way to describe a dc offset with a phasor because it does not have a phase angle. ....

That's probably true - never really thought about it. About the only times I have had to deal with DC offsets is with transformer energization, back-to-back capacitor energization, or bolted faults.

... We are in the wrong thread anyway.

I would agree. I'll stop if you stop.

ice

 

[iceworm]

Although the subtlety of your comments doesn't break any rules, and to the casual observer (or moderator), they seem meaningless;

Well that's good - I don't like breaking the rules.

... they are antagonistic. That eventually leads to comments in-kind, and then this all escalates until the thread closes. ...

I don't agree with your notions concerning IEEE 100. But, I don't want to see any escalation that would cause thread closure.

... I am open to carrying on a debate, but not under these terms.

I can't think of anything else that I could add that would bring in new ideas, reasoning, or information so I going to stay with, "I'm not comfortable continuing."

ice

 

[Rick Christopherson]

I can't think of anything else that I could add that would bring in new ideas, reasoning, or information ....

How about addressing how you think that IEEE contradicts what I stated above? I pointed out how the usage of the phrase "can be considered" doesn't contradict what I stated. Do you interpret that phrase to be more absolute?

 

[iwire]

Nothing in my previous posting, or postings throughout this thread, warrants the antagonism and animosity that you are displaying with your latest response. Although the subtlety of your comments doesn't break any rules, and to the casual observer (or moderator), they seem meaningless; to active participants, they are antagonistic. That eventually leads to comments in-kind, and then this all escalates until the thread closes.

All, there is a 'report post' button at the bottom left of each post, it is the triangle with the exclamation point.

If anyone has a problem with any post the way to handle it is to use the report post button, further posts like the above will be removed. Stay on topic.

 

[iceworm]

... Do you interpret that phrase to be more absolute?

Okay, At your urging, there is one (please, only one) thing I can add. It doesn't cover what you are asking, but perhaps it will better explain why I think the way I do.

If the math model I'm using treats impedance as a phasor, then I'm fine with that. If the math model I'm using treats the impedance as as pseudo-vector, then I'm fine with that. It really doesn't matter to me. As long as I am inside of the model limits - I'm fine.

The term "pseudo-vector", is from a post from rbalex (I think) a few yers ago, As I recall, the difference is an impedance vector noted as a + jb, does not have a physical direction.

rb -
appologies if I picked the wrong person. And if I picked the wrong person, appologies for not giving credit to the right person.

ice

 

[Rick Christopherson]

If the math model I'm using treats impedance as a phasor, then I'm fine with that. If the math model I'm using treats the impedance as as pseudo-vector, then I'm fine with that. It really doesn't matter to me. As long as I am inside of the model limits - I'm fine.

I don't think we are actually in any sort of disagreement here. All of the phasors and vectors we use in electrical analysis are actually pseudo-vectors, but we drop that term by common usage.

What has been forgotten here is where the notion of a phasor comes from. A phasor is a rotating vector. Mathematics did not create this name simply to allow Captain Kirk to kill Romulans. It was created to permit us to work with rotating vectors in the same space as static vectors. That is in fact, the very core of how we use vector analysis. The power sources are rotating vectors, but the loads are static vectors. We can't analyze these unless we put them all into the same model. Poof! The phasor was developed to suppress the rotational component of a rotating vector, and we can now use standard vector analysis to intermingle rotating vectors and static vectors.

As phasors, they are all static. The rotational component is suppressed, and they all become equal and fixed in their rotation. Contrary to a comment made in another thread, there is no such thing as a static-phasor, because they are all static. That term was confused with the term "static-vector". Some vectors are static and some vectors are rotational. The term "phasor" encompasses them all and makes them all non-rotational. Which is what permits us to analyze them using normal vector analysis.

 

[mivey]

After national/international consensus document defintions, I prefer standard textbooks. Most of them also have a fairly solid vetting process. Definitions gleened from the Internet are more problematic. This is not to say they are wrong, but they are rarely subject to peer review. My biggest mistake in the other thread was not starting off withthe IEEE defintion. Historically, as happened there also, people fixate on the note rather than the defintion. I should have just ridden with it.

There was nothing wrong with the definition or the accompanying note. I think the problem in the other thread was mis-application of the definition.

The IEEE definition talks about the phase of a particular wave. The phase is any point on the AC wave. To designate a particular phase, it must be indicated using some means. The IEEE definition is just saying that we indicate a particular phase by referencing it to a point or some particular phase of the wave and using the relative displacement as an indicator. The IEEE definition uses a fractional indictor for an individual wave. This particular IEEE definition does not extend to comparing the phases of multiple waves. That is covered by other definitions. The definitions covering multiple waves do incorporate the concept of phase, but they also further define how this concept is to be used.

When you used the phase indicator of an individual wave and extended that definition to cover comparing multiple waves, your result departed from the application of the definition as used by our industry. This departure was illustrated in dozens and dozens of reference and textbook and university lecture definitions, notes, and examples, as well as illustrations and examples from our members.

As I said in that thread, I understand where you were trying to get to, but you just went about it the wrong way. There were ways to make your illustration without running afoul of they way our industry relates phases between waves. The way you were applying the definition, any two waves with a 0? to 360? displacement could have the same phase. That is just not the correct way to apply the definition of phase.

 

[pfalcon]

Impedance is a scalar; being complex does not change it to a vector. It just makes the math more "complex"

The resultant of the product of a scalar * phasor (polar vector) is dependent on the direction of the phasor. Complex scalar values modify the direction of the resultant as well as the magnitude.

 

[Rick Christopherson]

Impedance is a scalar; being complex does not change it to a vector. It just makes the math more "complex"

The resultant of the product of a scalar * phasor (polar vector) is dependent on the direction of the phasor. Complex scalar values modify the direction of the resultant as well as the magnitude.

If that were true, then current and voltage could not have different phase angles. That pretty much would wipe out any need or desire for using vector analysis in solving circuits.

 

[pfalcon]

Impedance is a scalar; being complex does not change it to a vector. It just makes the math more "complex"

The resultant of the product of a scalar * phasor (polar vector) is dependent on the direction of the phasor. Complex scalar values modify the direction of the resultant as well as the magnitude.

If that were true, then current and voltage could not have different phase angles. That pretty much would wipe out any need or desire for using vector analysis in solving circuits.

How did you arrive at that conclusion? The imaginary part of the impedance changes the phase angles between them. You don't resolve a scalar and absolute it. You have to retain the imaginary portion for the math.

 

[Rick Christopherson]

How did you arrive at that conclusion? The imaginary part of the impedance changes the phase angles between them. You don't resolve a scalar and absolute it. You have to retain the imaginary portion for the math.

Well, then it's no longer a scalar. It is a vector.

 

[pfalcon]

Well, then it's no longer a scalar. It is a vector.

What's no longer a scalar? Having a complex component doesn't make it a vector. It just puts it in to 2D space instead of the typical pure 1D magnitude you normally see.

The most common complex scalar is "i", the square root of -1. It causes 90 degree rotation of the vector it's applied to.

http://www.euclideanspace.com/maths/algebra/realNormedAlgebra/complex/index.htm

 

[rbalex]

There was nothing wrong with the definition or the accompanying note. I think the problem in the other thread was mis-application of the definition.

The IEEE definition talks about the phase of a particular wave. The phase is any point on the AC wave. To designate a particular phase, it must be indicated using some means. The IEEE definition is just saying that we indicate a particular phase by referencing it to a point or some particular phase of the wave and using the relative displacement as an indicator. The IEEE definition uses a fractional indictor for an individual wave. This particular IEEE definition does not extend to comparing the phases of multiple waves. That is covered by other definitions. The definitions covering multiple waves do incorporate the concept of phase, but they also further define how this concept is to be used.

When you used the phase indicator of an individual wave and extended that definition to cover comparing multiple waves, your result departed from the application of the definition as used by our industry. This departure was illustrated in dozens and dozens of reference and textbook and university lecture definitions, notes, and examples, as well as illustrations and examples from our members.

As I said in that thread, I understand where you were trying to get to, but you just went about it the wrong way. There were ways to make your illustration without running afoul of they way our industry relates phases between waves. The way you were applying the definition, any two waves with a 0? to 360? displacement could have the same phase. That is just not the correct way to apply the definition of phase.

phase (of a periodic phenomenon ƒ(t), for a particular value of t)The fractional part t/P of the period P through which ƒ has advanced relative to an arbitrary origin.

Note: The origin is usually taken at the last previous passage through zero from the negative to the positive direction.

[IEEE Std 100 The IEEE Standard Dictionary of Electrical and Electronic Terms]

I know there is nothing wrong with the definition and I didn't misapply it. However, as I mentioned, at least one of your fellow “two-phase” advocates fixated on the Note by declaring that ONLY “the last previous passage through zero from the negative to the positive direction” be considered as the "origin". That is a patently false assertion. The "Note" mentions a convention, not a requirement.

It is necessary to understand what a phase is in the first place before you can begin to compare phases. I know how to apply the IEEE definition properly in that regard.

So UNLESS you can show the two line-to-neutral voltages for a conventional 120/240V system as functions of time :

• Aren’t periodic, AND
• Don’t have a common period P, AND
• Don’t have a common origin (by starting at the same time), AND
• Don’t have the identical t/P (phase) for any time t throughout the period, P.

THEN it is you that have misapplied or possibly failed to comprehend the definition as it applies to comparing functions with respect to phase.

There is NOTHING in the root definition that requires comparing ANYTHING other than t/P between the two functions.

Whether you and some of your fellow advocates don’t use the term phase that way is irrelevant; only comparing t/P between the two functions is still the proper application of the IEEE definition. It may mean you and those that agree with you cannot accept the definition beyond your preconceived notions. It seems to be the reason, one of your colleagues insists on asserting additional criteria outside the definition.

 

[Rick Christopherson]

What's no longer a scalar? Having a complex component doesn't make it a vector. It just puts it in to 2D space instead of the typical pure 1D magnitude you normally see.

The most common complex scalar is "i", the square root of -1. It causes 90 degree rotation of the vector it's applied to.

http://www.euclideanspace.com/maths/algebra/realNormedAlgebra/complex/index.htm

A scalar cannot change the direction of a vector, because the scalar has no direction itself. You're mixing complex numbers (rectangular coordinates) with your idea that vectors or phasors can only be polar coordinates. That is wrong, and that is why you are not realizing that complex numbers are every bit a vector.

 

[rbalex]

• Aren’t periodic, OR
• Don’t have a common period P, OR
• Don’t have a common origin (by starting at the same time), OR
• Don’t have the identical t/P (phase) for any time t throughout the period, P.

In fairness, the "AND"s should be replaced by "OR"s as above. That is, disproving any one of them would invalidate the basic argument. While developing the original "edit", I posited the statements affirmatively but forgot to make the proper operator (OR) when I restated them in in the negative.

 

[rattus]

Phase According to rattus:

Phase According to rattus:

This endless posting of phase defintions can be resolved easily.

According to definition #2 posted by rbalex.* Phase is simply the argument of the sinusoid describing the waveform.

phi(t) = (wt + phi0) where phi0 is the phase constant (phase angle)

Then it is a simple matter to deduce that if the phase angles of the static phasors describing the waves are equal, the waves are of the same phase. Otherwise, they are not of the same phase.

Obviously the periods of the waves are the same, and all use the positive real axis as a reference, and all are described by the expression:

120Vrms(cos(phi0) + jsin(phi0)) static phasor

Now if we let the phi0 be 0 and PI, that is the voltages are 120Vrms @ 0 and 120Vrms @ PI which are NOT of the same phase. That is all that needs to be said!

There are two opposing phase angles, two phases. Nuf Sed!

If we believe that a sinusoid and its inverse are of the same phase, we may as well not define phase!

*The definition can be found other places as well.

 

[mivey]

I didn't misapply it.

If we take misapply to mean applying it differently than the rest of our industry, then it is a misapplication.

However, as I mentioned, at least one of your fellow ?two-phase? advocates fixated on the Note by declaring that ONLY ?the last previous passage through zero from the negative to the positive direction? be considered as the "origin". That is a patently false assertion. The "Note" mentions a convention, not a requirement.

This point has been made. It was pointed out by all parties that other points could be used as an origin so there is nothing to debate since we are all in agreement.

It is necessary to understand what a phase is in the first place before you can begin to compare phases. I know how to apply the IEEE definition properly in that regard.

I'm sure we all understand that "phase" per the definition is an indication of a location on the wave.

So UNLESS you can show the two line-to-neutral voltages for a conventional 120/240V system as functions of time :

• Aren?t periodic, OR
• Don?t have a common period P, OR
• Don?t have a common origin (by starting at the same time), OR
• Don?t have the identical t/P (phase) for any time t throughout the period, P.

THEN it is you that have misapplied or possibly failed to comprehend the definition as it applies to comparing functions with respect to phase.

The IEEE definition of phase does not discuss:

• a common period P, OR
• a common origin (by starting at the same time), OR
• identical t/P (phase).

There is NOTHING in the root definition that requires comparing ANYTHING other than t/P between the two functions.

There is nothing in the root definition about comparing functions. Comparing the phase relationship between functions is covered in other definitions. A distance measurement from arbitrary start points does not show the phase relationship.

For example:
If we say the location of Joe on a 400 meter track is given by the % lap or the #meters he has traveled from where he started, that is equivalent to the t/P or percent of a period traveled by the wave. Comparing Joe's % lap or #meters with Frank's % lap or #meters does not describe Joe's position relative to Frank unless we define where they entered the track. In other words, the measurement (% period traveled, or the #seconds traveled) of the individuals does not define their positions relative to each other.

Same thing with time. Even if Frank and Joe have been running the same amount of time and at the same speed, that does not describe their relative positions on the track.

In a three-phase system, all of the waves start at the same time but we do not say they are in phase. To say the # seconds traveled defines the phase relationship is to say that two waves with a phase difference have the same phase. Although you have claimed that, I have challenged you several times to find a textbook or reference book that says that.

Whether you and some of your fellow advocates don?t use the term phase that way is irrelevant

So exclude my personal posts and examples, then exclude the dozens of other member's personal posts and examples, then you are still left with the dozens and dozens of textbooks, reference books, and class lecture notes that were presented that say that is the way to use phase when comparing functions.

only comparing t/P between the two functions is still the proper application of the IEEE definition.

The definition does not speak to comparing the phase of functions. That is covered by other definitions. None of those say that two waves with a phase difference have the same phase.

It may mean you and those that agree with you cannot accept the definition beyond your preconceived notions. It seems to be the reason, one of your colleagues insists on asserting additional criteria outside the definition.

We are using the definition the way the rest of our industry uses it as shown by the dozens upon dozens of posts with the criteria applied the way we have.

 

[rattus]

It is not clear from definitions 1 and 3, but t/P must include the phase constant in order to be compatible with definition 2, phi = (wt + phi0).

It is illogical to hold that the definitions are incompatible.

 

[rattus]

Why?

Why?

A three phase wye has three phases separated by 120 degrees, right? I thought so. So why is it somehow different with a split phase system with two phases separated by 180 degrees? Would it make any difference if we didn't know the source of the voltages? Why?