Indices for Harmonic Distortion Monitoring of Power Distribution Systems

Among the different power quality parameters, the voltage total harmonic distortion is important and is often studied. Different indices have previously been suggested to measure and monitor both the current and the voltage distortion in power systems, but the harmonic characterization of a power system can still not be performed in a satisfactory way. The state of the harmonic distortion is difficult to predict due to the variability and a large number of unknowns, such as detailed consumer and system characteristics. In this paper, a new index that describes the total harmonic distortion in the current measurements, i.e., the total rated distortion (TRD), is suggested to simplify and standardize the harmonic current measurements. Another index that represents the increase of the harmonic voltage distortion with TRD, i.e., the equivalent harmonic impedance z _eq, is proposed as an efficient way of characterizing a particular site. It is analyzed when z _eq is increased or decreased with regard to the angle between the harmonic voltages and currents. Finally, extensive harmonic measurements of a real distribution system were performed to prove the usefulness of the proposed indices.