Harmonic disturbances in networks and their treatment

Distorted waveform

Electricity is generally distributed as three voltage waves forming a 3-phase sinusoidal system. One of the characteristics of such a system is its waveform, which must always remain as close as possible to that of a pure sine wave. If distorted beyond certain limits, as is often the case on networks comprising sources of harmonic currents and voltages such as arc furnaces, static power converters, lighting systems, etc., the waveform must be corrected.

The aim of the present document is to provide a better understanding of these harmonics problems, including their causes and the most commonly used solutions.

Harmonic quantities

To help the reader follow the discussion, we will first review the definitions of a number of terms related to harmonics phenomena. Readers already familiar with the basic terminology may proceed directly to the next chapter. On AC industrial power supply networks, the variation of current and voltage with time is considerably different from that of a pure sine wave (see fig. 1 ). The actual waveform is composed of a number of sine waves of different frequencies, including one at the power frequency, referred to as the fundamental component or simply the “fundamental”.

Harmonic component

The term “harmonic component”, or simply “harmonic”, refers to any one of the abovementioned sinusoidal components, the frequency of which is a multiple of that of the fundamental. The amplitude of a harmonic is generally a few percent of that of the fundamental.

AUTHOR: Schneider Electric experts | Christian COLLOMBET, Jean-Marc LUPIN, Jacques SCHONEK