Earthing of Electric Distribution Systems

Earthing plays an important role in the safe and reliable operation of an electric network. The choice of earthing system, in both medium voltage (MV) and low voltage (LV) networks, depends on the type of installation as well as the network configuration. This chapter explains different methods of earthing equipment, distribution substations and MV and LV networks. System earthing or intentional connection of a phase or neutral conductor to earth is for the purpose of controlling the voltage to earth within predictable limits. The neutral earthing methods used in MV networks can be classified into five categories: direct distributed neutral earthing, direct nondistributed neutral earthing, neutral earthing via impedance, neutral earthing via a designated circuit, and unearthed neutral. In compliance with IEC standard, three main earthing systems are used: IT earthing system, TT earthing system, and TN earthing system.