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CHAPTER 1: THREE-PHASE POWER MEASUREMENT
1.4
Harmonic Distortion
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.
Current (amps)
1000
500
0
a
t
2a
–500
–1000
FIGURE 1–10: Non-distorted 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.
1500
Current (amps)
1000
500
0
a
t
2a
–500
–1000
–1500
FIGURE 1–11: Distorted current wave
The distortion observed in Figure 1.11 can be modeled as the sum of several sinusoidal
waveforms of frequencies that are multiples of the fundamental 60 Hz frequency. This
modeling is performed by mathematically disassembling the distorted waveform into a
1–14
EPM 2200 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE