Electro-thermal simulation of ZnO arresters for diagnosis using thermal analysis

Surge arresters are equipment of great importance for the protection of electrical systems. Their choice for a specific substation line or equipment must follow a rigid selection and testing. The maintenance of this equipment by the realization of regular monitoring also plays a major role for the system integrity. Arrester failure may result in an its explosion or system turn off. Thermographic inspection is one of the most used techniques for monitoring high voltage devices. It registers the temperature gradient along the equipments surface, indicating overheat. For zinc oxide (ZnO) arresters, this technique presents a limitation. Because of the low thermal conductivity of the porcelain or polymeric housing there is no direct relation between the temperatures on the housing surface and the temperatures on the varistors. A solution for this limitation is the development of computational routines to make this correlation. This paper presents a program based on finite difference techniques that makes the heat transfer over all the arrester indicating the temperature of any desired point. It considers both ceramic and polymeric housed arresters and can be used to simulate electrical tests defined in technical normative and to estimate the inner arrester temperatures when the outside temperatures are measured. A comparison between thermal dissipation for porcelain and polymeric insulated arresters is also presented.