The power stations and sub-stations generally house expensive equipment. These stations can be protected against direct lightning strokes by providing earthing screen. It consists of a network of copper conductors (generally called shield or screen) mounted all over the electrical equipment in the substation or power station. The shield is properly connected to earth on at least two points through low impedance. On the occurrence of direct stroke on the station, screen provides a low resistance path by which lightning surges are connected to ground. In this way, station equipment is protected against damage. The limitation of this method is that it does not provide protection against the traveling waves which may reach the equipment in the station.