Applicability of the dielectric response methods of diagnostics of power transformers: Hungarian experiences

The actual life of transformers strongly depends on the real operating conditions and the residual life of these units can spread in a fairly broad scale. The key factor is the presence of moisture and ageing products because they strongly influence the condition of oil-paper insulation. Therefore recent attention has been directed to methods of determining moisture content and ageing products in the transformer. There are two fundamental dielectric processes in transformer insulation: the conduction which is characterized by conductivity, and the polarization characterized by the polarization spectrum. Both processes are in very strict relation to the structure of the material. Any changing of the structure caused by the deterioration of insulation brings a typical alteration of the dielectric processes and the dielectric parameters of insulation as well. Thus the shape of polarization spectrum is characteristic not only to the insulation material, but to its deteriorating processes to its condition as well. Especially the long-time constant range of the polarization spectrum gives a lot of information about the deteriorating processes of insulation. The Hungarian results - one detail has been only shown in this paper - could improve the interpretation of results of spectrum methods; it is useful in evaluating the condition of the oil-paper insulation and allows observation of the progress of the aging and moistening process in oil-paper insulation.