Typical Defect Analysis and Disposal Research on Secondary Voltage Circuit of 10 kV Busbar

In response to the typical defect where "phase voltage shows no abnormal changes but only zero-sequence voltage increases" during single-phase grounding of a 10 kV busbar, this study identifies the root cause as wiring errors in the secondary circuit of PT through on-site fault recorder analysis, MATLAB modeling and simulation of equivalent circuits, and theoretical derivation. Specifically, in the 4PT connection scheme, the secondary winding of the neutral-point PT was not connected in series to the N-phase circuit, resulting in the loss of displacement voltage at the neutral point. In the 10 kV 3PT connection scheme, an open circuit in the secondary N-phase led to abnormal displacement voltage at the neutral point. Targeted rectification measures—such as connecting the winding in series and restoring the N-phase circuit—along with voltage-rise test verification, successfully restored normal secondary voltage connections in both substations.