Measurements of neutral currents and voltages on a distribution feeder

Abstract

Neutral currents flow in four-wire distribution systems due to linear load unbalances and triplen harmonics associated with mainly the magnetizing currents of (distribution) transformers. It is known that high levels of neutral currents can lead to overloaded/burned neutral conductors, common-mode noise problems, derating of transformers and/or excessive voltage distortion. The proliferation of nonlinear loads which inject harmonic currents into the distribution system has brought more attention upon the levels of neutral currents and voltages found in distribution systems. To this end, this paper evaluates measurements taken on the neutral conductors of a distribution feeder at two different sites. The analysis of the measurements focuses on the magnitudes of the triplen-harmonic currents and voltages relative to their corresponding phase RMS values in order to separate the impact on the neutral conductors of nonlinear loads and linear load unbalances.