(Proceedings on Seminar on Earthing Systems, 21-22, May, New Delhi, pp 23-34)
Grounding of large electrical installations of high earth resistivity poses-special problems particularly in mountains and rocky strata. Recommended low values of ground resistance are difficult to achieve for such cases, however, the installations can be made safe by limiting the potential gradients and by adopting special means. Safety is usually a concern only during abnormal electrical conditions like lightning strokes, phase-to-ground faults (two most frequent abnormal electrical conditions). With the objective to highlight some issues like, sizing of grid conductors and down leads from equipment to the grid, advantage of circular conductor over flats, ground rods, importance of the surface layer resistivity, and design of grounding system in a difficult situation, a case study for the Earthing System adopted at 400/220kV interconnecting sub-station at Malbase Bhutan is presented. The grounding system is a classic example of optimization of various factors of design without sacrificing safety concerns and stipulations.
