Grounding in Power Transmission and Distribution Networks

Power transmission and distribution systems are earthed for electric shock and fault protection. This chapter presents the principles and practices of grounding for power systems. An earthed power system usually refers to a system in which the neutral point of transformer or generator windings is intentionally grounded, either solidly or through impedance. Power system earthing should provide a sufficiently low impedance path, via the return conductors, back to the supply source to facilitate the operation of protective relays under fault condition. For the purpose of system protection, low earth fault loop impedance is desired so that resulting fault current is sufficiently high to operate the circuit protective devices. An effective method of preventing the hazardous touch voltage resulting from an earth fault is to create an equipotential zone within which all exposed‐conductive‐parts and extraneous‐conductive‐parts are essentially at the same potential. This local equipotential zone may be achieved by a proper system of grounding and bonding.