Harmonic Distortion - GE Grid Solutions Multilin 9450 Instruction Manual

CHAPTER 1: THREE-PHASE POWER MEASUREMENT
1.7

Harmonic Distortion

EPM 9450/9650 ADVANCED POWER QUALITY METERING SYSTEM – INSTRUCTION MANUAL
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:
where q is the angle between the voltage and the current (see Fig. 1.9).
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.
Harmonic distortion is primarily the result of high concentrations of non-linear loads.
Devices such as computer power supplies, variable speed drives and fluorescent light
ballasts make current demands that do not match the sinusoidal waveform of AC
electricity. As a result, the current waveform feeding these loads is periodic but not
sinusoidal. Figure 1.10 shows a normal, sinusoidal current waveform. This example
has no distortion.
1000
500
0
– 500
– 1000
Figure 1-10: Nondistorted Current Waveform
Figure 1.11 shows a current waveform with a slight amount of harmonic distortion.
The waveform is still periodic and is fluctuating at the normal 60 Hz frequency.
However, the waveform is not a smooth sinusoidal form as seen in Figure 1.10.
Displacement PF =
HARMONIC DISTORTION
cos
θ
Time
1–11