I. Medic, I. Sarajcev, and M. Majstrovic (Croatia)
Grounding, cable sheath, inductive coupling , earthing wire
An analytical method is presented to determine the line to-ground fault current distribution and related voltages in the earthing system which consists of two substation earthings interconnected by insulated metal sheaths of modern XLPE cables and one bare earthing wire laid in parallel in the same cable trench. The equations derived are based on the assumption of uniformly distributed conductance between the earthing wire and earth. The proposed method takes into account inductive coupling between cable sheaths and the earthing wire. The effects of connecting bare earthing wire parallel to insulated cable sheaths as well as that of their mutual inductance, are outlined. These effects may have significant influence on current and voltage distribution in earthing system. It is assumed that power cables operate in the network with non-directly earthed neutral point (e.g. 10 - 35 kV) so that relevant zero-sequence current is coming from another, directly earthed high voltage (h.v.) network.
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