Effect of moisture on accelerated thermal aging degradation of nomex insulation of dry-type transformer

Nomex insulation paper is the main turn-to-turn insulation material of dry-type transformer, and its life span determines the service life of the transformer. Temperature and moisture are the main factors that affect the aging degradation of Nomex insulation paper. The Nomex paper samples with different moisture contents (3%, 5%) were thermally aged under 180°C in order to study the influence of initial moisture on thermal degradation process of dry-type transformer. All the samples were periodically sampled and the degree of polymerization (DP) of insulation paper, frequency domain spectroscopy (FDS) and microstate were measured during the thermally aging process. The results indicate that, the higher the initial moisture content of the sample at the same temperature, the faster the DP of the sample decreases. However, the rate of the decline during thermal aging test is not constant but decreases with ageing time. From the FDS test results can be seen that with the increase of initial content, the real part of the complex permittivity (s') of Nomex insulation paper increases in the measuring frequency range, and dissipation factor (tand) of Nomex insulation paper increase significantly in the frequency range of 10
^-2
~ 10
²
Hz. And the microscopic observation results show the microstate changes of Nomex insulation paper with aging time.