Analysis of Polarization and Depolarization Currents of Samples of NOMEX®910 Cellulose–Aramid Insulation Impregnated with Nytro® BIO 300X

This paper presents the results of laboratory tests analysing the effect of accelerated thermal ageing on the temporal characteristics of polarisation and depolarisation currents, of transformer insulation samples made of NOMEX®910 hybrid cellulose-aramid electrical insulating paper, impregnated with Nytro®BIO 300X insulating liquid. The accelerated laboratory thermal ageing process consisted of annealing samples of the analysed insulation, at a number of selected temperatures, over a specified period of time. The temperatures and annealing times of the samples were chosen to replicate as closely as possible the ageing process of transformer insulation occurring during the long-term operation of power transformers in the structure of the National Power System. To determine the degree of ageing of the samples tested in the laboratory, the polarisation and depolarisation current analysis method (PDC Method) was used. The result of the analysis are regression functions of the activation energy and dominant time constants of the components of the cellulose-aramid insulation NOMEX®910, with consideration of the effect of temperature and the degree of thermal degradation of the cellulose fibres.