Calculation of current flow in grounding systems of substations and of HV line towers, in line shield wires and cable sheaths during earth faults

Abstract

The paper presents a method and a numerical calculation program of the repartition of the earth-fault currents in the grounding systems of substations and of the HV line towers, as well as of the currents which flow in the shield wires of the overhead lines and/or in the sheaths and armourings of underground cahles. The program may be applied also to very extended networks for single-phase-to-ground (1-Φ-to-Gr) and phase-to-phase-to-ground (Φ-Φ-to-Gr) faults at any point. The program is based on the simulations of the earth resistances of the HV line towers by means of a transversal conductance uniformly distributed between the shield wires and earth, and which is assumed to be variable from stretch to stretch according to soil resistivity. Models are derived which are aimed at simulating the single and double-circuit overhead lines provided with shield wires, as well as the underground cables. These models consist in a single three-pole or four-pole equivalent circuit. The validity of the program is verified by comparison with the calculations carried out by the Electromagnetic Transients Program (EMTP). Mention is made of a study carried out for the Turkish 420/150-kV network. Some measures presented are aimed at reducing the currents which flow in the shield wires of the lines outgoing from the power plants/substations following faults nearby.