GE EPM 6000 instruction manual Harmonic Distortion, Harmonics of a Non-Sinusoidal Waveform

CHAPTER 2: ELECTRICAL BACKGROUND

2.5Harmonic 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.

Current (amps)

1000

500

0

–500

–1000

a

FIGURE 2–10: Non-Distorted Current Waveform

t 2a

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.

	1500
	1000
(amps)	500
	0	t
Current
	a	2a
	–500
	–1000
	–1500

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

2–14 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE