Ground potential rise characteristics of urban step-down substations fed by power cables-a practical example

Ground Fault Current Distribution When a Ground Fault Occurs in Hv Substations Located in an Urban Area

“…Since (8) gives the relationship between complex quantities, it can be presented as the following system of two equations…”

“…After determining the relevant parameters of the equivalent conductor (R C and r C ), relations (8) and (9) can be used for obtaining: Z 1C , Z 0C and Z 1C , as well as: I c and I e (Fig. 4).…”

“…were in the past considered necessary [8]. Moreover, one can expect elimination of the strict requirement for the application of expensive MV cables acting as grounding conductors (cables with an uncovered sheath), as was the case with the MV distribution network of Beograd [14,15].…”

“…Somewhat later, the papers considering this problem in special cases, when a feeding line appears as a longitudinal combination of one cable and one overhead section, have been published, e.g., [8][9][10]. Also, several methods have been developed for solving this problem in cases where, because of a high local soil resistivity and/or a high short-circuit level, special measures aimed at reducing part of the ground fault current flowing exclusively through the earth (e.g., bare copper conductor laid in the same trench as the cable feeding line, counterpoises, etc.)…”

Analysis of ground fault current distribution along nonuniform multi-section lines

“…In particular, in case of a combined overhead-cable feeding line, most of the ground fault current which return through the cable sheaths will be dissipated into the soil surrounding the transition station (TS), where cables are connected to the overhead line [9][10][11][12]. This is due to the difference in coupling factors for cable and overhead lines ground return paths, so that only a small quantity of the return current carried by cable sheaths continues toward the remote source through the overhead ground wire.…”