3 phase instantaneous power measurement difference in measuring two methods

i have measured 3 phase instantaneous power active and reactive by two methods (1. using 3 phase instantanious measurement block; 2. measured 3 single phase power measurement block). I found that total active power measured both the methods is same (3331 watts) although there is difference is reactive power measurement: first methods it is -810.9 vars while in secoond method it is 832.4 vars. Reason?

Answer 1

[Ayush]

Hi Jaynendra,

I understand you’re seeing the same active power but different reactive power readings when comparing the 3-phase measurement block to the sum of three single-phase blocks.

This difference is because reactive power in a 3-phase system isn’t always just the simple sum of each phase’s value. Unlike active power, reactive power depends on the phase angle between the voltages and currents across all three phases. The 3-phase block measures reactive power by considering the overall interaction between the phases, essentially performing a vector sum, while the single-phase blocks just add up each phase separately, missing these interactions.

For this reason, the 3-phase measurement block provides a more accurate calculation of total reactive power in a 3-phase system, as it properly accounts for the phase relationships.

You can also refer to the following MATLAB documentation for the "3-Phase Instantaneous Power Measurement" block:

https://www.mathworks.com/help/sps/powersys/ref/power3phinstantaneous.html

Hope this helps.