Power Measurement Phasor behavior

[Xooch]

I downloaded the "LabVIEW code for Electrical Power Measurement from https://lumen.ni.com/nicif/us/codelvelectpwr/content.xhtml, and I have some issues with how it's operating.

Here's is the diagram of a VI I setup to play around with it (I realize that the phasor VI is set to 3 phase, but I can't seem to connect to the phasor diagram if it's set to single phase):

And here is a shot of the front panel, during steady state operation:

I have two issues - Why is the amount of measured power creeping up slowly? With the current waveform lagging the voltage waveworm this doesn't happen. It appears to only behave this way in the first three quadrants, but not IV.

Also - Why does my phasor diagram show both arrows pointing to +60 degrees? The voltage and current are out of phase and I would expect the voltage phasor to point to 0, and the current phasor to point to +60.

Thank you.

[Dan_N]

Hello,

I think the issue might be related to your use of the three-phase phasor VI, as I was not running into the same issue that you were with the phasor VI. It would be very helpful if you could post your code here, as then I could recreate the issue exactly.

Best,

Dan Nelson

Applications Engineer

[Xooch]

I've attached the actual VI. I believe it's the same as what is above. It's been a couple days.

[Dan_N · Accepted solution]

Thanks! After checking out your VI, I found the root of the problems here. If you look at the scale of your Power measurement while it's ramping up, you can see that the Y-Axis ranges from 300 to 300 Watts. The power is actually not increasing, but the autoscaling on the Power Waveform Chart makes it appear that it is. To fix this, simply right click the chart and deselect "Autoscale Y," and then you can set the scale limits to whatever you find appropriate.

As for the phasor problem, you have the Phasor Diagram VI wired incorrectly; if you look at the block diagram for your VI, you have the Current Phasor output wired to both the Current and Voltage Phasor inputs for the phasor diagram. Wiring the Voltage Phasor to the Voltage Phasor input to the Phasor Diagram VI will solve this problem. 

Best,

Dan Nelson

Applications Engineer

[dkuhinek]

Hi, I have made a similar simulation, in which I want the current phase increase from 0 to 90 degrees. As you can see in the code, I have used for loop to achieve that. The difficulty is that when I run it, the phasor function does not recognize the phase i.e. it is around 0 for every iteration. When I use fixed phase all seems to work fine. Does anybody has any clue where is the error? Thanks for any information about this issue.

[Xooch]

Dalibor,

When I was playing around with this I ran into the same problem as you.

The issue is the VI that's generating your signal isn't actually changing the phase of the signal, even though you're supplying a different value to the phase input. Wire a true constant to the reset input and run your VI, and it will work. The graphs look even cooler if you change your iterations to 90 and calculate for each degree of phase.

That VI and other like it have an internal state that's carried over from call to call.

[dkuhinek]

Thanks, this works.

I agree with you, using 90 loops and 1 degree increment makes this graphs look cool.

[Eswarsai123]

while I compiling your code it showing like sub vi's not found can you able to upload the sub vi's