Diagnóstico de falhas em pára-raios utilizando termografia

Abstract

Surge arresters are devices built to absorb and to drain to the earth the energy originated from lightning in the electric system that, otherwise, would damage the equipments in a substation. It behaves as an open circuit in normal conditions, and as a short circuit while lightning exists.However, these devices could degrade because of many agents along the time, especially pollution and humidity. Depending on the level of degradation it can damage the device resulting in a situation, which it does not get to maintain itself as an open circuit in normalconditions, what could cause an explosion. This event is critical, not only because of the extension of the damages caused to the equipment, but also because of the dangerous situation for the people's safety. Looking into minimize these occurrences it is necessary the standardization of an inspection methodology in surge arrester of substations. In the presentdissertation, the methodology was investigated based in thermography currently used by CEMIG (Energy Company of Minas Gerais) in the inspection of its surge arrester that consists of evaluating the temperature differences found along the body of the device, withimages taken in at least three different angles of vision. Were accomplished thermographic inspections in substations of 138 kV of CEMIG, evaluating the methodology according to theinfluence of the solar radiation, the presence of physical obstacles blocking the acquisition of images in same angles, the choice of the coefficient of emissivity of the material, the amount of vision angles adopted and the subsequent analysis of the termograms, the number of sub areas in what the device is divided and also according to the temperatures difference which are considered critical.