An earth fault diagnosis method based on online dynamically calculated thresholds for resonant ground systems

The primary problem of distribution system protection is single-line-to-ground (SLG) fault, particularly in networks with distributed generators (DGs), where asymmetrical phase sequence components caused by SLG faults may lead to system instability. Currently, the location and suppression methods of SLG faults are based on reliable fault diagnosis. Therefore, considering the imbalance of line parameters, this paper analyzes the fault characteristics of zero-sequence voltage (ZSV), and proposes a threshold-online-calculating-based SLG fault diagnosis method, which includes fault detection, fault occurrence moment capture and fault nature estimation. Firstly, the ZSV is measured in real time by the designed feeder terminal unit (FTU), which is embedded with the proposed SLG fault diagnosis method. Secondly, the ZSV signal is decomposed by the Mallat algorithm, and the fault diagnosis thresholds are calculated through the maximum margin hyperplane, which is used for fault detection and fault nature estimation. Finally, the fault occurrence moment is captured by variational mode decomposition (VMD) and its Teager Energy Operator (TEO). The proposed SLG fault diagnosis method has been tested in simulation and physical experiments in a 10kV system, the effectiveness and feasibility have been validated.