Evaluation of voltage imbalance on low‐voltage distribution networks considering delta‐connected distribution transformers with a symmetrical NGS

The main purpose of this study is to evaluate the effect of distribution transformers with a delta‐connected neutral‐grounded structure (NGS) on the voltage imbalance of low‐voltage distribution networks. The proposed NGS for delta‐connected distribution transformers has a symmetrical structure. That is, the stability and reliability of the operating characteristic of the proposed delta‐connected NGS are better than other grounding methods such as corner‐grounding, mid‐tapped grounding, a zig–zag grounding transformer, and an asymmetrical NGS. In this study, the coupling‐free equivalent circuit mathematical models for various methods of grounding a delta‐connected structure are first developed. Furthermore, these coupling‐free equivalent circuits can be simply implemented in the MATLAB/Simulink platform. Next, the IEEE test feeder system is used as a benchmark for verification. To determine the feasibility of the proposed NGS and evaluate its operational performance, a Monte Carlo simulation‐based three‐phase power‐flow method was proposed to compare the operational characteristics of various grounding structures (i.e. system imbalance resulting from asymmetric load conditions or asymmetric transformer connections) such as phase‐to‐ground voltages, line currents, power consumption, and voltage unbalance factor. The results provide a valuable reference for distribution engineers and building technologies seeking a suitable method of grounding delta‐connected power service systems.