Power factor, reactive, active and apparent power

[EduU]

Good morning,

I have a VI that make some math calc and give me the power factor from the system, but when I'm trying to show it in a waveform graph I have some problems.

First I have to fix the scale: -1 to 1 

Second that you all know if the values go high than 1 the value has to be negative -0.999 -0.98 

How could I work on Y axis to change it when I'm trying to show a graph of power factor? I think about use property node to work on Y axis... but maybe have an easier way!

And also if someone know an easier way to calculate power factor, Reactive, Active and Apparent power I would be glad if someone can help me on that!

Thanks

[JÞB]

I'm thinking that we could be more helpful if we could see the code you have.  Please attach your vi so we don't have to guess how you've done it.

[EduU]

Hey Jeff,

This program  was made in LabVIEW 7.1

I will upload the code but I will tell here more or less what it do.

You won't be able to run the problem because it's open a file that I have recorded with another program and save a new file.

To get real power (p) = I took the average of instantaneous power 

P=V x I

Apparent power (S) =  Vrms x Irms

Reactive power (Q) = SQRT (S^2 - P^2)

Power Factor = P/S

This is the math, the problem is I need to adjust the graph to power factor

and we know that power factor goes -1 to 1

How can I make LabVIEW understand if a value go high than 1 so it's negative? my problem is that!

I will make a second post to upload the other 2 VI's

Message Edited by EduU on 03-12-2010 06:12 AM

[EduU]

The other 2 VI's

[Henrik_Volkers]

This might be what I understood you asked for ..... Slide is your calculated powerfactor and numeric is the wrapped 1 to -1  value.

Fixing the scale is done by right click the scale and uncheck autoscale and set max and min by clicking at the end values and set the value you want. This can be done with property nodes as well in the diagram.

Message Edited by Henrik Volkers on 03-12-2010 01:41 PM

[EduU]

Yes, I know how to fix the scale

But the problem is

When the number is > than  1 isn't 1,1 or 1,01 it's -0,99 -0,98

So I think something like that:

Put the Y to start at 1, and below that is positive

after that is negative

like:

-0,88

-0,90

-0,92

-0,94

-0,96

-0,98

1

0,98

0,96

0,94

0,92

0,90

0,88

But, how can i do that at Y-scale?

[EduU]

I have another question:

How can I measure power factor negative?

The formula is: PF = P/S

P is real power always is positive

S is apparent power and the formula is: Vrms x Irms so it's always positive too

So how could I know if PF is capacitive?

Thanks

[EduU]

No one!? =/

Please I really need help on that!

Thanks

[tbob]

You should compare the output of P/S.  If less than or equal to 1, then leave it alone.  If greater than one, then subtract 1 minus the PF.  This gives a negative number.  I'm not quite sure about the 1 minus PF, but I think this is what you want.

[JÞB]

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EduU wrote:

I have another question:

How can I measure power factor negative?

The formula is: PF = P/S

P is real power always is positive

S is apparent power and the formula is: Vrms x Irms so it's always positive too

So how could I know if PF is capacitive?

Thanks

---

Unfortunatly you cannot get there with RMS voltages and currents.  To determine reactive elements you need the phase relationship between the Voltage and current.  If voltage and current are in phase the system is resistive.  an inductive system will have voltage leading the current by the ratio of L-R (see pathagoras for a formula)  and in a capacitive system the voltage lags the current.