Characterisation of earthing systems under high frequency and transient conditions

Earthing systems in distribution and transmission networks are designed to provide adequate safety levels under normal operating and fault conditions. It is well known, however, that designs made for power frequency operation have a different response under high frequency and transient conditions. Such conditions arise during fault and switching transients as well as when the system is subjected to lightning strikes. This paper reviews current recommendations and practice for high frequency and transient earthing system design. It also describes simulation studies of various earthing scenarios under variable frequency and transient conditions. These include surge arrester earthing electrodes, tower bases and substation grids. The effect of electrode arrangements, mesh dimensions and above-ground conductors were quantified.