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.
Basic Construction of Earthing Screen
The basic construction of earthing screen involves network of copper conductors also usually known as shield or screen. The layout of the earthing screen depends on the specific requirements of the power system and the components to be protected. Factors such as fault current levels, system voltage, and physical dimensions of the equipment play a role in determining the screen’s design.
Installation of Earthing Screen
The conductive wires or strips are installed in a mesh-like arrangement around the equipment or area to be protected. They are typically spaced at regular intervals to ensure uniform grounding. The shield is properly connected to earth on at least two points through a low impedance. The earthing screen is bonded and interconnected with other grounding systems within the power system, such as the equipment grounding system and the overall grounding grid. This ensures proper coordination and continuity of the grounding system.
Limitation of Earthing Screen
Although earthing screen is quite effective for protecting expensive electrical power equipment at power stations, yet it has one limitation. An earthing screen does not provide protection against the travelling waves which may reach the equipment in the station.
Also see Power System Protection MCQs
References and Further Recommended Reading
- V. K. MEHTA, R. M. (2022). Principles of Power System (LPSPE). India: S CHAND & Company Limited.
- Rajput, R. K. (2006). Power System Engineering. India: Laxmi Publications Pvt Limited.