The method of sequence networks is still well-known and widely utilized for analyzing and computing unsymmetrical faults in power system networks today, particularly in solid grounding systems where it was initially introduced for short circuit analysis. When it comes to single-phase earth fault that is a dominant majority type of fault in power distribution grids, different neutral grounding methods with varied impedances result in distinct fault characteristics, to continue utilizing sequence networks could cause inaccurate calculations by the reason of neutral voltage during earth fault does not remain as close to zero as it's pinned in solid grounding system. As neutral resistance increases gradually, the impact of line-to-ground capacitance becomes more pronounced and can no longer be ignored. In this case, applying sequence networks could lead to calculated results that are far from the actual situations in grids. This paper discovers and proves an obscurely hidden defect of the sequence network, while proposing a new and novel modeling to derive comprehensive equations of fault calculations for all types of resistant grounding systems, including solid grounding, low resistance grounding, high resistance grounding, and ungrounded systems.
