Three-phase isolated power transformer based novel structure for power distribution system and new theoretical/practical judgement criteria in detecting high-impedance earth faults

Single phase-earth faults are the most frequent faults likely to occur but hard to identify in distribution system, especially in a neutral un-effectively grounded system. To address this issue, this paper innovatively proposes a typical distribution system structure, in which it only introduces one three-phase isolated power transformer (PT)-based subnetwork division mode that can effectively limit the zero-sequence current flow from other sound lines. Second, following the qualitative discussions about the effect of the proposed structures on power supply reliability and probability of bushfires caused by high impedance earth faults (HIEFs), a novel detecting judgement criterion merely using vector-based variation via pre-fault and post-fault zero-sequence voltage is mathematically formulated. In general, the proposed structure takes into account the the fault current suppression while manifesting fault feature at the same time, and in contrast with current detecting methods, vectorized form can present a wider exploring space and a higher identifying sensitivity, especially in detecting HIEFs. Numerical simulations and field tests validate the effectiveness and adaptability of the proposed detecting approach towards single phase-earth fault identification field.