Is power a phasor or vector or neither?

[rattus]

I say neither because the expression for real instantaneous power involves a dc offset modulated by a sinusoid of frequency 2wt.

Phasors cannot represent the dc offset. And what about the phase angle, how would it apply to a wave of T/2?

Some think that the power triangle proves that power is a vector, but here we simply use complex numbers to represent real and imaginary power. Also, the power triangle always falls in the first quadrant.

BTW, we have been around this block before.

 

[T.M.Haja Sahib]

A DC offset component can not be present in circuits with purely inductive or capacitive components.In such cases.......?

 

[rattus]

A DC offset component can not be present in circuits with purely inductive or capacitive components.In such cases.......?

But the instantaneous power in a reactive circuit is:

p(t) = VI*cos(theta) - VI*cos(2wt - theta)

Clearly, VI*cos(theta) is a dc offset.

 

[iwire]

Is a phasor or vector a concept or an obsession?

 

[T.M.Haja Sahib]

But the instantaneous power in a reactive circuit is:

p(t) = VI*cos(theta) - VI*cos(2wt - theta)

Clearly, VI*cos(theta) is a dc offset.

In a purely reactive circuit with no resistance, VI*cos(theta) is absent so that the power is a phasor just like a current or voltage.

 

[rattus]

In a purely reactive circuit with no resistance, VI*cos(theta) is absent so that the power is a phasor just like a current or voltage.

But, this is a special case. The statement must be true for all conditions. Plus, what is the meaning of theta? Theta is merely the lead/lag angle of the current, +/- PI/2---the power factor angle.

 

[rattus]

Is a phasor or vector a concept or an obsession?

It is a little of both. The phasor is a powerful tool which greatly simplifies AC calculations. And, many engineers don't fully understand phasors and the difference between phasors and vectors. Frankly, when I joined this forum I didn't fully understand them either, but I dug into my old texts and doped them out.

It is my obsession to spread the TRVTH about phasors from time to time--as long as there are people willing to have a discussion.

 

[T.M.Haja Sahib]

The statement must be true for all conditions.

Nor is yours.

I say neither

 

[K8MHZ]

Is a phasor or vector a concept or an obsession?

Here is a Vector that didn't make it past the concept phase.

View attachment 6705

 

[charlie b]

Neither. Power is the rate of producing, or using, energy. Phasors, vectors, sinusoids, and other such things are methods of modeling a physical phenomenon. The physical is the physical, and the model is the model, and never the twain shall meet.

 

[steve66]

Neither. Power is the rate of producing, or using, energy. Phasors, vectors, sinusoids, and other such things are methods of modeling a physical phenomenon. The physical is the physical, and the model is the model, and never the twain shall meet.

I couldn't say it any better than that.

If you have ever seen technical textbooks geared to a 2 year Associates degree in electronics, you may find that those students are frequently given a very in depth course in AC analysis without phasors.

AC waveforms and impedences are represented by vectors, and all the usual circuit laws apply the same as if phasors were being used. No phasors necessary.

Obviously, many things can be represented by phasors, vectors, or even real numbers (RMS values). It all depends on what you need to calculate, or what you want to model.

 

[steve66]

It is my obsession to spread the TRVTH about phasors from time to time--as long as there are people willing to have a discussion.

If I could find a nicer way to say this I would, but I 'm not sure why you think you are more qualified to "spread the truth" than others on this forum.

 

[rattus]

If I could find a nicer way to say this I would, but I 'm not sure why you think you are more qualified to "spread the truth" than others on this forum.

There are probably others more qualified than I, but they don't seem to have the obsession; if they do let them have at it.

 

[rattus]

I couldn't say it any better than that.

If you have ever seen technical textbooks geared to a 2 year Associates degree in electronics, you may find that those students are frequently given a very in depth course in AC analysis without phasors.

AC waveforms and impedences are represented by vectors, and all the usual circuit laws apply the same as if phasors were being used. No phasors necessary.

Obviously, many things can be represented by phasors, vectors, or even real numbers (RMS values). It all depends on what you need to calculate, or what you want to model.

I would venture to say that the AS textbooks had not been updated to use the term "phasors" instead of "vectors". There are differences. For example, if you treat the voltages in a split phase stem as force vectors, the opposing forces cancel yielding 0V between L1 and L2. But if you treat them as phasors, you subtract one from the other to obtain 240Vrms.

 

[ggunn]

There are probably others more qualified than I, but they don't seem to have the obsession; if they do let them have at it.

In this, as in many other things, there is a considerable amount of disagreement about exactly what the "TRVTH" is.

 

[ggunn]

I would venture to say that the AS textbooks had not been updated to use the term "phasors" instead of "vectors".

Are you saying that something changed or that they were wrong all along?

 

[rattus]

In this, as in many other things, there is a considerable amount of disagreement about exactly what the "TRVTH" is.

That is the point, to get to the TRVTH, whatever it is.

 

[rattus]

Are you saying that something changed or that they were wrong all along?

Yes, they quit using the term 'vector' in favor of the term 'phasor'. At lease some people did maybe 50 or 60 years ago. A vector describes something with a magnitude and direction in space such as force, velocity, field strength, etc. A phasor describes something with a magnitude and phase angle (time) such as a sinusoidal voltage or current. In fact, phasors are limited to sinusoidal waveforms with the exception of impedance.

My AC Circuits text, first copyrighted in 1935, later copyrighted in 1951, uses vectors, while a later text, copyrighted in 1960, uses phasors.

 

[steve66]

Yes, they quit using the term 'vector' in favor of the term 'phasor'. At lease some people did maybe 50 or 60 years ago. A vector describes something with a magnitude and direction in space such as force, velocity, field strength, etc. A phasor describes something with a magnitude and phase angle (time) such as a sinusoidal voltage or current. In fact, phasors are limited to sinusoidal waveforms with the exception of impedance.

My AC Circuits text, first copyrighted in 1935, later copyrighted in 1951, uses vectors, while a later text, copyrighted in 1960, uses phasors.

Once again, your "search for the truth" has led you to make incorrect assumptions. It's not at all a matter of later texts using phasors and earlier texts using vectors. Its a matter that either can be used to represent AC circuits and the voltages and currents in the circuit.

Here is a 2008 article in a magazine most people in this forum will recognize, and it uses vectors for circuit analysis:

http://ecmweb.com/training/electrical_basics/electric_basics_vector_analysis_2/

There are differences. For example, if you treat the voltages in a split phase stem as force vectors, the opposing forces cancel yielding 0V between L1 and L2. But if you treat them as phasors, you subtract one from the other to obtain 240Vrms.

That's completely incorrect. Either method applied properly will give the same 240v answer. It should be pretty obvious that if vectors could be used to find the correct answer in 1951, then the same vectors can still produce the correct answer today.

(ggun: looking back, I see you were thinking the exact same thing. )

 

[rattus]

Once again, your "search for the truth" has led you to make incorrect assumptions. It's not at all a matter of later texts using phasors and earlier texts using vectors. Its a matter that either can be used to represent AC circuits and the voltages and currents in the circuit.

Here is a 2008 article in a magazine most people in this forum will recognize, and it uses vectors for circuit analysis:

http://ecmweb.com/training/electrical_basics/electric_basics_vector_analysis_2/



That's completely incorrect. Either method applied properly will give the same 240v answer. It should be pretty obvious that if vectors could be used to find the correct answer in 1951, then the same vectors can still produce the correct answer today.

(ggun: looking back, I see you were thinking the exact same thing. )

"The term 'vector' which has been used by electrical engineers to mean a complex number, should be avoided because of confusion with space vectors (such as the force vectors in field theory). The rules for vector algebra as used by mathematicians are not the same as the rules for the algebra of complex numbers."

[Tang, Alternating Current Circuits, International, 1960]'''

I think it is a matter of terminology, the older texts simply called the phasors vectors because of the similarities and because the term 'phasor' had not been pushed by the AIEE. No big deal, really.