Single-Phase Isolated PT Based Novel Structure for Power Distribution System and New Theoretical/Practical Judgement Criteria in Detecting High Impedance Earth Faults

Over a long time detecting high impedance earth faults (HIEFs) and suppressing the forest fire danger commonly caused by edge-phase-type single phase-earth faults in an ineffectively grounded system are of high concerns. To address this problem, this paper innovatively refines the structure of distribution system via a single-phase power transformer (PT) isolated subnetwork division mode, and optimizes the voltage distribution among three phases by introducing an additional capacitance, which is extremely conducive to control arc ignition commonly occurring in two edge-phases while line-to-line voltage are still equal to the original state. Second, to augment detecting sensitivity in HIEFs, a novel detecting judgement criterion merely using the vector-based variation via pre-fault and post-fault zero-sequence voltage, is theoretically derived, and compared with traditional methodologies it can possess a higher detecting ability. Numerical simulations and real-field tests effectively and fully demonstrate the adaptability and potentials of the proposed structure and approach toward single phase-earth faults.