### Q

I’m developing a electric meter based on the ADE7878. The meter is calibratedand working fine. However, I’m trying to show the power factor and the

cos(phi) for the different lines and the 3-phase.

To obtain the power factor I divide the instantaneous active power by the

instantaneous apparent power for every line. For the 3-phase value I add all

instantaneous active powers and then I divide it by the sum of all

instantaneous apparent powers. But for the cos(phi) I’m not very sure how I can

obtain it. Can I extract it for the angle measurements of every line? If not,

any ideas?

### A

When the voltages and currents do not have harmonics, the cos(phi) is equal tothe power factor. When there are harmonics, I believe you would like to compute

cos(phi) only on the fundamental. The ADE7878 provides the angle between the

fundamental components of the voltages and currents on each phase. One can

compute the cosine of these angles and obtain the cos(phi)/power factor on the

fundamental on each phase. This is useful when someone needs to compensate the

inductive reactive power to bring the power factor up as the capacitors that

are normally used are computed based on the fundamental power factor. See

section Time Interval between Phases, page 33, rev E ADE7878 data sheet.