Design practice for the earthing system of the 400 kV gas insulated switching station at Lavrion

The paper presents the situation of the gas insulated 400 kV switching station at Lavrion of Public Power Corporation, Greece as a part of a power station expansion project and gives details of the ground grid design. Although the ground grid design was carried out according to the American Standard IEEE 80 "Guide for safety in AC substation grounding", there is a cross reference to the German Standard DIN VDE 0141 "Earthing systems for power installations with rated voltages above 1 kV" and the upcoming European Standard EN 50179 "Erection of electrical power installations in systems with nominal voltages above 1 kV AC". Besides the analysis of soil resistivity and the selection of conductor sizes, the determination of fault current distribution in the grounding system is a key step for the design of an effective and economically feasible grounding system. Finally, the test procedure for verification of effectiveness of the earthing system after completion of erection is given.