The earthing screen is a network of copper conductors (generally called shield or screen) that is generally mounted over the electrical equipment in an electric power station.
An Electrical substation houses expensive electrical equipment and devices. In case of lighting thunders, there is a chance that lightning strokes might directly hit the equipment at the power station. The power station can be protected against direct lightning strikes by providing an earthing screen.
Earthing screen is also known as an earthing shield. The earthing shield should be connected to the earth at, at least two points. In case of lightning strokes, the earthing screen provides a low resistance path by which lightning surges are diverted to ground thus providing protection to the station equipment.
Also see Power System Protection MCQs