Axial voltage and gradient distribution of metal oxide surge arresters

An investigation of the external axial voltage and gradient distribution along the porcelain shells of metal oxide arresters was conducted. Various service conditions such as on ground or elevated installation, proximity to energized apparatus or large earthed objects, and their influence on the voltage and gradient distribution were studied. It was found that if an EHV arrester designed for on ground installation is erected on a tall slender pedestal, then the voltage gradient along its bottom section is greatly increased. If such an arrester is operating in a polluted environment the increase in voltage gradient in one location may cause external surface arcing and excessive voltage stresses on zinc-oxide blocks in that part of the arrester. Such a situation can be effectively improved by fitting a bottom grading ring, the shape of which can be determined through a modeling procedure. Both computer modeling and experimental techniques were used in the analysis and close agreement between the theoretical and experimental results was obtained. An innovative, fast, and simple method of measurement was developed and extensively tested on 500 kV surge arresters