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CHAPTER 2: ELECTRICAL BACKGROUND
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–13
So keeping the var content low allows a line to carry its full capacity of watts. In order to
encourage customers to keep VAR requirements low, most utilities impose a penalty if the
var content of the load rises above a specified value.
2.4.2 Power Factor
A common method of measuring reactive power requirements is power factor. Power
factor can be defined in two different ways. The more common method of calculating
power factor is the ratio of the real power to the apparent power. This relationship is
expressed in the following formula:
(EQ 2.1)
This formula calculates a power factor quantity known as Total Power Factor. It is called
Total PF because it is based on the ratios of the power delivered. The delivered power
quantities will include the impacts of any existing harmonic content. If the voltage or
current includes high levels of harmonic distortion the power values will be affected. By
calculating power factor from the power values, the power factor will include the impact of
harmonic distortion. In many cases this is the preferred method of calculation because the
entire impact of the actual voltage and current are included.
A second type of power factor is Displacement Power Factor. Displacement PF is based on
the angular relationship between the voltage and current. Displacement power factor
does not consider the magnitudes of voltage, current or power. It is solely based on the
phase angle differences. As a result, it does not include the impact of harmonic distortion.
Displacement power factor is calculated using the following equation:
(EQ 2.2)
where θ is the angle between the voltage and the current (see FIGURE 2–9: Voltage and
Complex Current on page 2–12).
In applications where the voltage and current are not distorted, the Total Power Factor will
equal the Displacement Power Factor. But if harmonic distortion is present, the two power
factors will not be equal.
Total PF
real power
apparent power
----------------------------------------
watts
VA
--------------==
Displacement PF θcos=