Moisture migration in oil-impregnated film insulation under thermal ageing

Abstract

Moisture produced in thermal degradation of insulating materials in transformer causes damage to the insulation system. To study the moisture diffusion and balance process in transformer insulation system and evaluate alternative insulation materials, three types of samples, including Kraft insulation paper, PC and PET film, were impregnated in oil and thermally aged under 90, 110 and 130 °C respectively. By analysing the moisture variation in oil and solid insulation, it was found that the moisture diffusion, balance and hydrolytic degradation process of oil-paper insulation are different from those of other two types of samples. During the thermal ageing process, the moisture produced by polymer is much more than that by oil, and most of which is absorbed by sample surface. The ageing temperature has considerable influence on the moisture migration in polymers.

Modified Expression of Moisture Diffusion Factor for Non-Oil-Immersed Insulation Paper

“…2, the changing tendency of DP is in consistent with the results reported in [26], [27]. Additionally, the lifespan of insulation paper can be estimated by the following empirical formula [26]:…”

Effect of the oil‐paper insulation aging on partial discharge characteristics in a hemispherical surface model

“…According to previous research [19][20][21], the extent of thermal aging of insulation pressboard mainly depends on temperature and time. The accelerated thermal aging method is used to process the pressboard, and the aging life is estimated according to the Montsinger rule [22,23]: the higher the working temperature of the insulating board, the shorter the insulation life. To reduce the time taken for each experiment, it is necessary to increase the aging temperature.…”

Simulation for Transient Moisture Distribution and Effects on the Electric Field in Stable Condition: 110 kV Oil-Immersed Insulation Paper Bushing

“…The radial electric field strength for each layer can be calculated by: (11) Then, according to Eqs. (9), (10) and (11), the following can be obtained:…”

“…Hence, the overload capability of OIP bushing is restricted, and the temperature field distribution should be clear before evaluating the overload capability of an OIP bushing [6], [7]. Besides, temperature is the fundamental and direct factor that determines the thermal aging status of oil-paper insulation, thus for estimating the life-span of OIP bushing, the temperature field distribution should also be clear [8]- [10]. In terms of the thermal sources of an operating OIP bushing, the dielectric loss of insulation under the effects of applied electric field is one of the most important sources [11], [12].…”