A New Approach in Defining Harmonic Indices in Power Utility Application

Abstract

This paper proposes a new method for current harmonic evaluation. Several harmonic indices have been defined for this purpose among which the Total Harmonic Distortion (THD) is the most widely used one. However, all these indices suffer from some deficiencies such as giving the same weight to all harmonic orders, and not giving a clear relation between the harmonics and their effects on system equipment. In this paper, for the first time, an index is defined based on current harmonic effects on transformers and power lines. A new formula is defined in order to determine the share of each harmonic order. The paper also proposes a new harmonic limit for the derived index. The limit is based on the de-rating of a transformer subjected to harmonic environments in order to keep its life equal to that of the same transformer when handles only fundamental current. In order to compare the effectiveness of the new index, several real cases with the same THD level are evaluated using the proposed index.