Research On Insulation Characteristics Of Oil-immersed Bushing Based On Frequency Domain Dielectric Method

Oil-immersed bushing is usually used for long periods of time in complex environments such as humidity and temperature changes,it will cause the insulation properties of the bushing to decrease,even caused equipment failures and major economic losses in the power grid.Therefore,it is important for the stable operation of the power grid to explore the technology and method of evaluating the insulation state of oil-immersed bushing under the influence of humidity and temperature changes.This paper adopts the guiding ideology of combining frequency domain dielectric method and molecular simulation method.Select oil-immersed bushing as the test object,and conduct frequency domain dielectric experiment under different moisture levels and different temperature conditions;At the same time,the molecular simulation technology is used to analyze and track the micro evolution of the insulating paper and oil-paper structure in the bushing,and find out the internal relationship between the micro structure mechanism and the macro insulation properties.According to the design standard,this article makes capacitor core which conforms the experimental requirements,and conducts a wet-heat aging test to prepare the same batch of oil-immersed bushing samples with different micro water content,then carry out frequency domain dielectric experiments to explore the effect of moisture on the frequency domain characteristics of bushing,and select the characteristic frequency point from the spectrum curve to evaluate the wet state of the bushing;conducting the frequency domain dielectric experiment of a single micro water content oil-immersed bushing under different temperature conditions,study the influence of temperature on the bushing spectrum curve;Using molecular simulation method and selecting the same experimental parameter to investigate the microscopic change of cellulose chain and oil-paper structure.The main research results are as follows:?1?In the frequency range of 10^-1Hz-10Hz,the spectrum curve of the oil-immersed bushing shows a rising law with the increase of micro water content,and selects 0.1Hz,1Hz,10Hz as the characteristic frequency point to fit the evaluation formula of the bushing damp state.?2?In the frequency range of 10^-2Hz-10Hz,the spectrum curve of oil-immersed bushing is positively correlated with temperature in the range of 20?-70?;In the frequency range of10Hz-10³Hz,the spectrum curve is positively correlated with temperature in the range of50?-70?.?3?Using molecular simulation technology to construct cellulose structure models with different water molecular mass fractions,extracting and analyzing the change about the mean square displacement,electrostatic force,potential energy and equilibrium state,and getting conclusions consistently with the frequency domain dielectric experiment results.?4?Building a composite model of cellulose chain and oil-paper structure to conduct research under different temperature conditions,Obtaining and analyzing the change law of mean square displacement,radial distribution function and equilibrium state,and exploring the relationship between the microscopic evolution characteristics and the macro electrical parameters about cellulose chain and oil-paper structure.In this paper,a research model that combines macro experiment and micro mechanism to explore the evaluation method of the oil-immersed bushing in humid and variable temperature environment,this method has a certain reference value and guidance for the detection of the insulation state of the running bushing.