excel graph in time domain for V(t), I(t), P(t), VAR(t), and apparent power

[badgers]

I think VAR(t) is a meaningful concept to help understand the process.
To make a power meter I would think everything is done with time domain calculations.
thanks again
PS, I think you did a great job on fixing the spreadsheet:thumbsup:

 

[Besoeker]

I think VAR(t) is a meaningful concept to help understand the process.
To make a power meter I would think everything is done with time domain calculations.
thanks again

You can present voltage as a time varying function. A sine wave. Similarly with current.
But VA is rms voltage times rms current.

Think about what rms actually is.
The square root of the mean of the squares.
That mean is taken over a period of time.
So you can't represent it in the same way as v(t)

PS, I think you did a great job on fixing the spreadsheet:thumbsup:

If that's addressed to me, then thank you!

 

[Smart $]

You can present voltage as a time varying function. A sine wave. Similarly with current.
But VA is rms voltage times rms current.

Think about what rms actually is.
The square root of the mean of the squares.
That mean is taken over a period of time.
So you can't represent it in the same way as v(t)

But V*A = W for both instantaneous computation and where the power factor is 1.0. Just as we express voltage and current as RMS for it to be single-term meaningful for a period of time, we express VA and W as an average. These values are computed over full cycles of voltage. However, how would you compute the values for a period of time which is not a multiple of a full cycle? Say you were actually computing watt-hours to six decimals (being overly pedantic :blink. Would you not have to consider the instantaneous values through time domain calculation?

If that's addressed to me, then thank you!

I believe that was addressed to me, but I'll thank you for your contribution to this discussion... :happyyes:

 

[badgers]

Here are the images as links to the full scale versions.
The first is a picture that I am trying to duplicate somewhat but I cant find the source for it.
http://daugird.com/cantfindsource.png

as I study the spreadsheet and the above graph which inspired me to start this endeavor, I notice in the linked graph, power does go negative.
I wonder what the difference is between the current spreadsheet and the graph.
PS I did find the source.
http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6995/report/F

Thanks again everyone.

 

[GoldDigger]

You integrate the mathematical value of the product function using all sorts of tricks and tables to get s function you can work with or you approximate the answer using a computer to calculate the area of thousands of tiny rectangles.

Tapatalk!

 

[Besoeker]

But V*A = W for both instantaneous computation and where the power factor is 1.0. Just as we express voltage and current as RMS for it to be single-term meaningful for a period of time, we express VA and W as an average.

But I can calculate instantaneous W from instantaneous values of I and V. To get VA I'd first have to calculate RMS values for V and A.

However, how would you compute the values for a period of time which is not a multiple of a full cycle?

Just extend the series on my spreadsheet.

Say you were actually computing watt-hours to six decimals (being overly pedantic :blink. Would you not have to consider the instantaneous values through time domain calculation?

You could do it that way.

 

[Smart $]

as I study the spreadsheet and the above graph which inspired me to start this endeavor, I notice in the linked graph, power does go negative.
I wonder what the difference is between the current spreadsheet and the graph.
PS I did find the source.
http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6995/report/F

Thanks again everyone.

The linked graph has some errors...

The line labeled P_total(t) should be s(t) for apparent power (the total is unnecessary), as it appears to represent v(t) * i(t). Also the reason the curve goes negative.

The line representing reactive power should be q(t). Also note it appears to be leading reactive power, yet the current is lagging the voltage.

Real power is not shown... P(t).

 

[Smart $]

But I can calculate instantaneous W from instantaneous values of I and V. To get VA I'd first have to calculate RMS values for V and A.

But if the period of time was infinitesimally short, we would be approaching instantaneous and therefore W ? VA, as V ? v(t) and A ? i(t)

ETA: the question marks were supposed to be the approximately equal symbol. dang forum limitations.

Just extend the series on my spreadsheet.

You could do it that way.

 

[Besoeker]

But if the period of time was infinitesimally short, we would be approaching instantaneous and therefore W ? VA, as V ? v(t) and A ? i(t)

Except that instantaneous VA has no meaningful context.
You rate a transformer in VA, kVA, or MVA.
RMS Volts times RMS Amps.
The "M" meaning mean precludes instantaneous values.

 

[Smart $]

Except that instantaneous VA has no meaningful context.
You rate a transformer in VA, kVA, or MVA.
RMS Volts times RMS Amps.
The "M" meaning mean precludes instantaneous values.

Meaningful is relative to the one doing the perceiving.

Yes "M" precludes instantaneous, and that's why I said infinitesimally short period of time.

 

[Besoeker]

Meaningful is relative to the one doing the perceiving.

Yes "M" precludes instantaneous, and that's why I said infinitesimally short period of time.

I think your second point answers your first.