Appendix 9 Definitions
A 20
Power Factor
(PF/DPF)
Power factor is the ratio of effective power to apparent power. The larger the ab-
solute value of the power factor, the greater the proportion of effective power,
w
hich provides the power that is consumed, and the greater the efficiency. The
maximum absolute value is 1. Conversely, the smaller the absolute value of the
power factor, the greater the proportion of reactive power, which is not consumed,
and the lower the efficiency. The minimum absolute value is 0.
For this device, the sign of the power factor indicates whether the current phase is
l
agging or leading the voltage. A positive value (no sign) indicates that the current
phase is lagging the voltage. Inductive loads (such as motors) are characterized
by lagging phase. A negative value indicates that the current phase is leading the
voltage. Capacitive loads (such as capacitors) are characterized by leading phase.
The power factor (PF) is calculated using rms values that include harmonic com-
ponents. Larger harmonic current components cause the power factor to deterio-
rate. By contrast, since the displacement power factor (DPF) calculates the ratio
of ef
fective power to apparent power from the fundamental voltage and fundamen-
tal current, no voltage or current harmonic component is included. This is the same
meas
urement method used by reactive power meters installed at commercial-
scale utility customers' facilities.
Displacement power factor, or DPF, is typically used by the electric power system,
al
though power factor, or PF, is sometimes used to measure equipment in order to
evaluate efficiency.
When a lagging phase caused by a large inductive load such as a motor results in
a
low displacement power factor, there are corrective measures that can be taken
to improve the power factor, for example by adding a phase advance capacitor to
the power system. Displacement power factor (DPF) measurements can be taken
under such circumstances to verify the improvement made by the phase advance
capacitor.
Demand
Denotes the average power [kW] consumed during the demand period (typically
30 minutes), and is used for power company transactions.
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