Investigation of transformer banks with delta‐connected secondary windings and various grounding methods for delta service

Grounding at source transformers or generators in a distribution system can help to stabilise system voltages and enhance overall reliability and safety. However, the operational characteristics of a distribution system depend on the type of grounding method employed. This study examines the operation characteristics of three‐phase transformer banks with delta‐connected secondary windings using a variety of grounding methods for three‐phase three‐wire or three‐phase four‐wire delta secondary services. The grounding methods investigated in this study include two conventional methods and a neutral grounding structure, called grounding winding. The authors began by developing coupling‐free equivalent circuits of three‐phase transformer banks with delta‐connected secondary windings in accordance with the network‐overlapping technique and circuit theory. These equivalent circuits faithfully reflect the features of the transformer banks with the various grounding methods. Then they implemented coupling‐free equivalent circuits using the software package MATLAB/Simulink to verify the suitability of the equivalent circuits for this study. The authors’ analytical results reveal that this neutral grounding structure provides a solid system neutral through a grounding winding as well as a voltage steadier than that obtained under ungrounded conditions or using corner‐grounding or mid‐tap grounding. Their results provide a valuable reference for power engineers seeking a suitable grounding method for delta service systems.