Insulation diagnosis of high voltage apparatus by partial discharge investigation

Investigation of properties of dielectric materials has the fundamental purpose to understand their behaviour once subjected to service stresses and to provide a feedback to material designer and manufacturers. However, an important by-product of such investigation is to single out diagnostic properties, that can allow evaluation of the state of electrical apparatus where these materials are employed. Most of electrical apparatus, in fact, fail due to breakdown or loss of performance of insulation. Therefore, a subtle, but strong, link exists between base material investigation and the development of diagnostic properties for electrical insulation systems. Purpose of this paper is to deal with diagnosis of insulation systems of electrical apparatus, referring in particular to partial discharge detection, which is becoming one of the most effective diagnostic techniques. Problems, limitations and advantages of this technique will be discussed in this paper, showing paramount examples of applications on cables and machines.