davidbeach said:
Wow. And here I’ve made it through nearly an entire career believing what I learned working on my Bachelors Degree - power factor is the ratio of the magnitude of real power to the magnitude of apparent power. Since both magnitudes are, definitionally, positive, it seems likely that the result will be positive.
IEEE Standard 100 has this as the definition of
arithmetic power factor and definition (B) of
phasor power factor. It's pretty much the basis of the IEC power factor sign convention based on the fundamental frequency. However, remember that real power isn't always positive -- it's defined to be negative per passive sign convention when the device is a source. The IEC power factor sign convention takes this into account, so loads always have a positive power factor sign as they have positive real power and sources always have a negative power factor sign as they have negative real power. This sign convention agrees with textbooks that define power factor as the cosine of the load impedance angle, since in Quadrants I and IV, which both have positive real power, the cosine of any angle is positive. In Quadrants II or III, which both have negative real power, the cosine of any angle is negative.
The IEEE power factor sign convention seems to be based on the relationship between the fundamental voltage phasor and fundamental current phasor. IEEE convention appears to use IEEE Standard 100 definition (A) of
phasor power factor to determine the power factor sign, which is "defined by the cosine of the phasor angle between the fundamental sinusoidal phase voltage and the fundamental sinusoidal phase current." If the current phasor lags the voltage phasor (an inductive/lagging load), the angular difference of current with respect to voltage is defined to be negative, and the IEEE convention states the power factor is negative. If the current phasor leads the voltage phasor (a capacitive/leading load), the angular difference is positive, and the IEEE convention states the power factor is positive.
xnuke
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