how to know when the voltage is over the X-axis

[Ray.R]

Please post what you have done so far, so that I can suggest how to improve what you have attempted.

It sounds like this is a college/university project.

[EduU]

Yes, this will be my unniversity project

but also is my work too!

Well I already measure a lot of things, like Voltage, Current, Real power, Apparent Power, Reactive Power

but now I'm trying to measure the Power Factor.. and to do it... I need the angle lag of voltage to current, or currento to voltage .... with this angle I can use the formula: ( (Vi x Ii)/(Vn x In) ) * cos X

Where Vi x Ii is the fundamental, and I need know how can I measure it

Vn x In I already have calculated... is the Vrsm x Irms

Cos X is the angle I have to find

So I need a help on how to measure power factor... and I have to know the signal if is positive so my system is inductive and if is negative my system is capacitive!

Thanks

[Ray.R]

Since it is for your project, I will help as much as I can without doing your project 😉

After all, you need to have a bit of fun, right?  😄

For instance, if you wanted to code the formula that you provided in LabVIEW, it would look something like this:

So you'll need to come up with the formula (or algorithm) to determine the angle lag.  Or at least describe how you want to implement the solution.  Then I can suggest how to do it in LabVIEW.

As for the signal being positive or negative, you'll have to set the rules to determine how to interpret the signal.  That can be coded as well.

R

Message Edited by Ray.R on 03-22-2010 08:38 AM

[EduU]

Yes, Ray

I need some fun now haha

Well I was looking the Electrical Power VI from NI, and there is a VI that calculate this angle... so I'm trying to improve it in my program, my other problem is to calculate the fundamental voltage and current... this one I think will be hard

I know I have to calculate it using spectrum, but at the moment all I tryed, I failed! haha

Could you give me a little help on fundamental? like another way to find... or how can I use spectrum at my program...

Thanks Ray

[Ray.R]

You'll have to describe how to measure the power spectrum.  Usually, when you talk about spectrum, I think about power levels (dB) over a span of frequencies.

So that means, what instrument do you use, signal conditioning, probe, what measurements you have to work with, and any pertinent information related to that calculation.

You may have mentionned it somewhere, but what frequency or frequency range are we talking about.

Can you summarize the requirements specifications related to your project?

Also, can you describe what went wrong with the "Electrical Power.VI" that you mentionned and why it didn't work for you?

It's been many years since I dealt with Power Factor Corrections or anything related to harmonics within power systems..  I'm quite rusty..

As you probably know, an electrical system supplies power to loads by delivering current at the fundamental frequency, where it provides real power.  When current of a single frequency is present in a system, you can use the measured values in Ohm's Law and power calculations.  For multiple frequencies, you need to add the RMS currents (Irms):

Irms = SQRT(I1**2 + I2**2 + I3**2 + I4**2 +...)

The same holds true for voltages.  For multiple frequencies, you need to calculate the RMS Voltage (Vrms).   I'm sure you know this, but here is a link to wiki's definition for RMS: http://en.wikipedia.org/wiki/Root_mean_square

To add to the above is the consideration for single & multi-phase power distribution (star / delta).

Having fun?  😉

R

[EduU]

Well, this one is for my work, so let me try explain that.

Frequency is 60Hz in Brazil.

I'm trying to measure power spectrum with the Data I wrote in another program... I read it and use the FFT power spectrum.VI but it never works nice for me.... I don't know why haha

Well the Electrical power.vi works nice... but I have some problems like...

It gives me the angle lag from voltage to current, but I have 3 voltages and 3 currents... so I have to compare Vr with Ir, Vs with Is so I think I have to give the number of the channel I want. I'm working on that but at the moment nothing special to say.

My biggest problem, I think is to find the fundamental. Today my boss told me that some friend of him talked about hilbert filter that gives me the fundamental without any harmonic. So I'm taking a look at LabVIEW to understand it better.

With the fundamental and the angle lag I can calculate the power factor from each phase and all I need is that!

Hope finish it soon, so I can give more attention to my unniversity project!

Thanks Ray, if you know something about this hilbert filter at LabVIEW or another wat to find the fundamental I would be glad if you can help me!

Message Edited by EduU on 03-23-2010 07:39 AM

[Ray.R]

Here is a link to knowledge base topic on Hilbert Filter: http://zone.ni.com/devzone/cda/tut/p/id/723

You can find the VI in the Functions Palette, under Signal Processing > Transforms.  You can also do a Search in the Functions Palette and it will find it for you.

Also have a look at this thread on phase differences between 2 sine waves  http://forums.ni.com/ni/board/message?board.id=170&message.id=411730&query.id=1071736#M411730

 Look at what SMercurio proposes to determine the phase differences.  He provides a link to Extract Single Tone Information

http://zone.ni.com/reference/en-XX/help/371361B-01/lvwave/extract_single_tone_info/

HEre is where you find the transforms in the Functions Palette:

Message Edited by Ray.R on 03-23-2010 11:02 AM

[EduU]

My problem is I don't have a signal to use the electrical power VI.... or the sine waveform....

I have an array of numbers of 2 dimensions.

Have some way to transform an 2D-array in a signal ??

or how can I use the electrical power VI with an 2D-array?

=/

[Ray.R]

I have not seen your code or the 2D array, but usually, you can read the 2D array and use Spreadsheet to 2D array (set to double) and you have a 2D array of numbers.  Those numbers represent your signal, do they not?

Can you post your 2D array?  And your code?  I'll suggest how  to do it.

R

[EduU]

My code is here:

It's in LabVIEW 7.1 I need to take this 2D-array after the for loop and make this a signal

Thanks