Possible Measures to Enhance the Performance of Metal–Oxide Arresters in the EHV Network Under Very Fast Transients

It is well known that metal-oxide arresters (MOAs) do not have the capability of protecting the equipment in extra-high voltage networks, when they face the threats from very fast transients (VFTs). This “inaction” on the part of MOA is mainly brought by stray capacitance, which not only delays the conduction of MOA under VFTs but also brings a nonuniform voltage distribution across its structure and thereby impacts its life, especially, that of its top unit. This phenomenon prompts an urgent take on the factors that threaten the functioning of MOA under VFTs. After performing a thorough review of the studies made earlier, this study focuses on the further improvements required. This paper mainly deals with the accurate calculation of stray capacitance, its adverse impacts on MOA during its conduction phase, voltage distribution across the arrester with the aid of a finite-element method (FEM) and the Electromagnetic Transient Program (EMTP), and, finally, it explores the modifications required to get adequate protection for the equipment exposed to VFTs.