Analysis of Current and Voltage Unbalance from Distribution Systems with High DER Penetration

Abstract

Variable single-phase distributed energy resources (DER), such as solar photovoltaics (PV) have the potential to increase the magnitude and variability of distribution system current and voltage unbalance potentially making conventional phase balancing approaches ineffective. High current unbalance can reduce feeder power transfer capacity and increase losses. High voltage unbalance is a power quality problem that can adversely impact some loads. This paper presents a detailed analysis of current unbalance on 44 distribution feeders and voltage unbalance on 38 substation transformer banks with high DER penetration within Southern California Edison (SCE) service territory. The magnitude, variability, and other characteristics of current and voltage unbalance are analyzed in detail. In particular, the impact of single-phase DER on current and voltage unbalance is analyzed. The many lessons learned are discussed, including the need for increased visibility to distribution power quality at high DER penetration levels.