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7816 Reactive Energy measurements with nasty loads.

Question asked by dBC on Jun 6, 2014
Latest reply on Jun 18, 2014 by hmani

I'd like to revisit this topic, last discussed over a year ago in this thread:

 

Reactive energy registers.

 

If you've got a relatively long integration period (say 10 seconds),  and a really nasty looking current signal, should tan-1(reactive/real) always come out pretty close to real/(Vrms*Irms), or does reactive energy get "lost" as discussed in that previous thread?

 

When I've got a nice clean current signal (leading or lagging), the power triangle as described above works fine, but the minute I start feeding it a really nasty load (like pictured below), my reactive energy readings come out way smaller than expected.  For the signal pictured for instance, my calibrated readings come out at:

 

Vrms = 254V

Irms = 1.029A

RealPower = 217W

ReactPower = -10.3VARS

 

so the power triangle is kinda' broken.

 

What is the algorithm used for calculating ReactEnergy?  I thought the device simply delayed one signal by 90 degrees and re-calculated the sigma(V*I).  And yet when I apply that algorithm in my spreadsheet, with the data in the picture, I get a ReactPower of about 39.4VARS which works out much closer to what the power triangle would suggest.  So it seems the device has some other algorithm for calculating reactive energy.

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