Development of Calculation Method for the Occurrence Rate of Short-Circuit Following Multi-Phase Flashover due to Lightning in Medium-Voltage Distribution Lines

Abstract:
To assess lightning outage rates on medium-voltage (MV) distribution lines using electromagnetic transient analysis programs, researchers typically equate the presence of multiphase flashovers (FOs) to the occurrence of short-circuit currents (or permanent faults) in calculations. However, observations from actual distribution lines have indicated that even in instances of multiphase FOs, short-circuit currents may not flow, and this does not invariably result in permanent faults. Therefore, this study investigated the circumstances under which fault arcs persist and short-circuit currents occur after multiphase FOs via lightning impulse tests superimposed on AC voltage. Our results indicate that reducing the short-circuit current facilitates the cessation of arc discharge, consequently lowering continuation rates. Then, we devised a methodology for calculating the incidence rate of short circuits after a multiphase FO, incorporating insights from the test results. Applying this methodology to a simulated distribution line revealed that the occurrence rate of short circuits, as determined by our proposed approach, is lower than that derived from the conventional method, which presumed an equivalence between the presence of multiphase FOs and the occurrence of short circuits. Hence, this study elucidated that the sustained state of fault arcs is a critical parameter in evaluating lightning outage rates.