Analyzing the Harmonic Levels at Power Lines to Improve the Power Quality

Abstract

Harmonics are one of the power system parameters which have not been intensively investigated despite its immense adverse effects on both the power utility and the power consumers. Harmonics distortion can be defined as an electrical noise or electrical pollution. It is usually a superposition of signals which are exact multiples of fundamental frequency. The amplitude of a harmonic is quoted as a percentage of the fundamental frequency. An important characteristic of harmonics is that they are transmitted upstream from the load to the transformer’s secondary windings, back to the service entrance and eventually to the utility distribution line.  Most of the dominant harmonics in the system are triplens (3rd, 9th, 15th etc) which are generated mainly by single phase non linear loads and usually causes overloading of the neutral conductors (contains zero sequence components; I_o and V_o). Other are odd harmonics (5th, 7th, 11 etc) generated by three phase non –linear loads (negative sequence components; I₂ and V₂). Examples of these kinds of non- linear loads are inverters/ rectifier and switching mode power supplies (SMPs) among others. The harmonics has adverse effects on both the power utility and the power consumer which includes transformers overload and failure of capacitor banks among other immense effects. From the investigation carried out, it has been established that large power consumers supplied on low voltage (415V) have their harmonics current level far beyond the threshold limit as defined by the IEEE 519-1992. In additional, Voltage distortions on transmission voltage were also noted are high Vis-a –vis the current distortions when measured at substation bus bars.