GE Multilin EPM 6000 - Harmonic Distortion

2–14 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE
CHAPTER 2: ELECTRICAL BACKGROUND
2.5 Harmonic Distortion
2.5.1 Harmonics of a Non-Sinusoidal Waveform
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. The following figure shows a normal, sinusoidal current waveform with a period
of a. This example has no distortion.
FIGURE 2–10: Non-Distorted Current Waveform
The figure below 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 (a = 1/60
second). However, the waveform is not the smooth sinusoidal form seen above.
FIGURE 2–11: Distorted Current Waveform
The distortion above 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 reducing the distorted waveform into a collection of higher
–1000
–500
0
500
1000
t
Current (amps)
a
2a
–1000
–500
0
500
1000
t
Current (amps)
a
2a
–1500
1500