235 / 2022-03-14 21:15:40

Research in wide temperature range dieletric characteristics of transformer oil-paper insulation based on FDS

oil-paper insulation,Arrhenius model,Mott VRH model,dielectric response,Dc conductivity,oil viscosity

Purpose/Aim

Oil-paper insulation is an important part of oil-immersed power equipment, so it is very important to evaluate its insulation state accurately. China has a vast territory and the temperature difference between north and south can reach more than 50℃. Different from high temperature environment, transformer oil phase state changes in oil-paper insulation on low temperature, the dielectric property of paper insulation changes obviously. In order to obtain the oil paper insulation state at different temperatures accurately, it is necessary to find out the changing rule of dielectric properties of transformer oil-paper insulation in wide temperature range and the influence of transformer phase change on the electrical conductivity of oil-paper insulation. Finally, the equivalent frequency-temperature relaxation model of oil-paper insulation should be constructed in different temperature ranges.

Experimental/Modeling methods

In this paper, electrical parameters such as frequency domain dielectric response, DC conductivity and physical and chemical parameters such as transformer oil viscosity and cardboard polymerization degree of transformer oil and oil-impregnated paperboard with different aging degrees within a wide temperature range (-60℃-100℃) were tested by experiments. The dielectric curves in frequency domain of high temperature region (0℃-100℃) and low temperature region (-60℃-0℃) were analyzed respectively, and the activation energy of oil-paper insulation was significantly different from that of oil-paper insulation by quantitative calculation. Based on this, Arrhenius model and Mott VRH model were used to characterize the dielectric response characteristics of oil-paper insulation at high and low temperatures respectively. According to the test data, the relationship between the aging degree of oil-paper insulation, test temperature and transformer oil viscosity was established, and the quantitative characterization equation between viscosity and dc conductivity of transformer oil was obtained.

Results/discussion

Through FDS test, it is found that the dielectric response curves of oil paper insulation in frequency domain are obviously different between high temperature region and low temperature region. Arrhenius model and Mott VRH model were used to characterize the dielectric properties of oil paper insulation. According to the calculation of the test data, the activation energy of oil-paper insulation in the high temperature region is basically unchanged, while in the low temperature region, with the decrease of temperature, transformer oil phase changes, viscosity increases, activation energy of oil-paper insulation decreases significantly, electrical conductivity decreases significantly.

Conclusions

In this paper, the frequency domain dielectric characteristic curve of oil-paper insulation in wide temperature region is obtained, and the dielectric relaxation model of oil-paper insulation at high and low temperature is constructed respectively, which provides theoretical reference for the evaluation of oil-paper insulation state.