Ans : Substation earthing system comprises neutral earthing, earthing of substation equipment and auxiliaries and earthing of noncurrent carrying metal frame work. For earthing substation equipment and auxiliaries, a peripheral G.I. strip earthing ring is installed to which all earth electrodes (spaced at about 3 meters interval) are connected and securely bonded by cross-connected G.I. strip conductors thus forming an earthing grid. The body of equipment and the structural frame work are connected to the earthing grid by two earth connections each. The transformer neutral is connected directly to two separate electrodes by strip conductors. The bases of lightning arrestors are connected directly to the separate earth electrodes by conductors as short and as straight as practicable. These earth electrodes are interconnected with the main earthing system to obtain low impedance between the lightning arrestors and the equipment.