Significance of grounding and earthing in a substation

This article takes us through a brief walkthrough on the key critical aspects towards installation of grounding and earthing systems in an electrical substation.

An electrical substation is a critical resource in a power system. A properly designed and installed grounding system is essential for a substation’s safe and reliable operation for its entire service life. A good grounding path of sufficiently low impedance ensures successful relay coordination during a fault. Faulty relay coordination may lead to an upstream trip or sustained fault. A sustained fault may not only cause thermal, mechanical, electrical, and electromagnetic stresses on substation equipment but may also lead to network instability.

Grounding or earthing in the substation 

The substation grounding system involves all types of grounding and bonding equipment systems, including a lightning grounding system, overhead ground wires, surge arresters, grounding mechanisms, and all uncharged metallic structures present in the substation, including the fence and access point. These structures are joined through a network of conductors with an appropriate size to sustain a fault and maintain a near zero potential throughout the substations during normal and fault conditions.

Substation Grounding Methods 

There are different methods for grounding a substation.

Grounding for assorted distribution equipment 

A substation’s remote and assorted equipment is connected to one or more grounding electrodes. Though economical, the earth pits may develop dangerous surface potential during a ground fault or lightning. If such systems are located in a populated area, it is mandatory to provide a Remote Fault-time Earth Resistance Monitoring system (RFERM®) and a suitable boundary to limit access near the system.

Grounding for indoor substation equipment 

A ring grounding conductor is installed along the perimeter of the building. Multiplicity, tiers of the ring, number of earth rods, etc., are decided on the limiting parameters prescribed by the designer as per relevant standards. The ring may also surround assorted equipment foundations. Short connections are made from the ring into the building. The health of neutral earth pits and lightning protection earth pits may need to be continuously monitored using a Remote Fault Time Earth Resistance Monitoring system (RFERM®), a patented technology designed by Manav Energy.

Grounding for outdoor substation equipment 

An earth grid is used to ground the switchyard with an air-insulated circuit breaker. All the unenergized parts of substation equipment and other earth points are grounded to a buried earth mat having redundancy. Conductors are buried horizontally, forming a grid-like structure to transfer the fault current to its source. The conductor is sized as per IEEE 80–2013 to withstand asymmetrical fault currents. However, dangerous potentials are calculated for substations protected by electronic or electromechanical relays. The health of neutral earth pits, lightning protection, and surge protection earth pits may need to be continuously monitored using a Remote Fault-time Earth Resistance Monitoring system (RFERM®).

Using IIOT Earthing and Lightning Management and Alert Systems (LMAS) 

Implementing IIoT technologies to monitor and maintain deteriorating earth grid conditions, earth pit conditions, and increased dangerous potential assists the O&M team in addressing the issue in a timely manner and saving replacement costs. These systems are designed to provide performance alerts to designated personnel with a date and time stamp using the latest communication technology. Additionally, LMAS is a lightning management and alert system that can predict and alert the development of lightning conditions and strikes, respectively, to O&M personnel. This helps the O&M team to alert people in the vicinity to move themselves to protected areas and bring the electrical network to a safe zone. Both technologies always enhance preparedness with safe and reliable operations.