Chapter 24 - Power Quality – Harmonics in Power Systems

Abstract

This chapter provides a summary of the main international regulations on power system harmonics, and a table of IEC standards. It explains the nature of harmonics in power systems followed by a review of the sources of such harmonics. It provides the major effects of harmonics in the power supply followed by a discussion of current methods of limitation. It also discusses ferroresonance and subharmonics, and concludes with an explanation of the nature of harmonic studies and their importance in modern system design. The term “power quality” refers to the purity of the voltage and current waveform, and a power quality disturbance is a deviation from the pure sinusoidal form. Harmonics superimposed on the fundamental are one cause of such deviations, and the chapter describes the nature, generation, and effects of harmonics on power supply systems, together with the limitation of such effects and harmonic studies. The widespread and increasing use of solid state devices in power systems is leading to escalating ambient harmonic levels in public electricity supply systems. These harmonic levels are subject to limitations to safeguard consumers' plant and installations against overheating and over voltages. It is also incumbent upon individual consumers to ensure that their equipment does not produce harmonic levels that exceed such limits at the point of common coupling with other consumers. These are called “emission limits.” Immunity standards set down the disturbance levels which equipment should be capable of tolerating without undue damage or loss of function. A third set of standards, for “compatibility levels,” has the function of enabling coordination and coherence of the emission and immunity standards.