| When a ground fault occurs in a power network with grounded neutral, the fault (zero sequence) current returns to the source station through the neutral conductors, grounding structures and ground. The calculation of fault current distribution between the neutral conductors and ground is important for the design and operation of power systems. A new calculation method is proposed to examine the segment-by-segment distribution of the sheath current along underground cables. The method uses both lumped and distributed parameters. The model consists of an equivalent phase conductor, the cable sheath, and grounding structures. The zero sequence current distribution between the sheath and the ground is solved through the computation of driving point impedances. Calculations related to the model have been done on a computer; various case studies and parametric studies have been conducted on a specific three conductor cable. The shielding effectiveness of the cable sheath has also been investigated. It was found that the sheath current distribution is strongly influenced by the sheath admittance to ground. The effects of other influencing factors (soil resistivity, grounding rod resistances, fault location, number of source stations, and substation grounding grid impedance) have also been calculated and analyzed. |
