Ground grid design of a transition station system-a typical example of fault transfer

E.T.D. Barra Funda I urban station, located in Sao Paulo, Brazil, is surrounded by several buildings, so it is not possible to make reliable earth resistivity and ground electrode resistance measurements. The grounding of this station was designed by using external circuits connected to the ground mat (sheaths and bare copper bondings). The use of these circuits allows a transfer of the fault potentials from E.T.D. Barra Funda I to E.T.R. Barra Funda II due to a strong cable shielding. A discussion is presented of the basic procedures adopted for controlling the potential rise at the E.T.D. Barra Funda I station in order to ensure the safety of people and equipment during the occurrence of a fault to the ground. This study deals with such design aspects as: high short-circuit level, high soil resistivity and backup protection time, and reduced area for diffusion of short-circuit current