Quantitative Contribution by Each Different Load Group to the Seventh Harmonic Voltage in an Electric Power Distribution System

Abstract

Although the number of pieces of equipment that emit harmonic currents has increased, harmonic voltages in Japan have gradually decreased since about 1999. In addition, harmonic voltages are generally lower during the daytime when there is greater usage of different types of equipment that emit harmonic currents. As a first step, we showed the reason for these strange phenomena qualitatively. The phase angles of the fifth harmonic current emitted by three-phase equipment of consumers using a 6.6kV or higher voltage power supply and those by the other equipment are almost opposite and they cancel each other out. As a second step, we classified equipment of all consumers into six different groups depending on the number of phases (i.e., single-phase or three-phase) and consumers' supply voltage and the ratio of the contribution of each group to the fifth harmonic voltage was then quantitatively clarified. As a third step, in this paper, we analyzed the seventh harmonic current in the same way as the fifth harmonic current. Time trends of the fifth and the seventh harmonic voltages are different but the estimated results of effective power of each group are almost same.