Research On The Moisture Evaluation Of Oil-paper-insulated Equipment Based On Equivalent Circuit Model

Oil-paper-insulated equipment is one of the most important and widely-used equipment in power grids.The insulation performance of the equipment tends to go down due to its long-term operation under complicated environment that is subjected to temperature,moisture,mechanical stress and certain chemical corrosion.Among these factors,moisture will seriously decrease the dielectric withstand strength of oil-paper insulation,therefore,it is of great realistic importance to accurately and effectively assess the moisture in oil-paper insulation for a reliable operation of power equipment.The dielectric response method,explored and summarized by many researchers,is a nondestructive testing method to assess the insulation moisture.Among them,frequency domain spectroscopy(FDS)is widely used because of its wide measurement frequency range,rich information and strong anti-interference ability.However,the current interpretation of FDS is limited to a simple comparison of tested FDS curves with reference samples,which can only provide a qualitative estimation of the insulation status.To overcome this shortcoming,by employing OIP condenser bushings as research objects,the dielectric characteristics of moistened oil-paper insulation are further investigated in the present study from the perspective of the broadband equivalent model of oil-paper insulation based on FDS measurement.The work been done is summarized as follows:(1)The cases of artificial damping of the condenser bodies in the OIP condenser bushings are designed and implemented,and an experimental platform for bushings test is also set up.The FDS tests for bushings under different moisture contents and different temperatures are carried out,and how the temperature and moisture affect the frequency domain spectroscopy of bushings is also analyzed in depth.(2)Based on the experimental data obtained from FDS results of the bushings,the broadband extended Debye model of oil-paper insulation is obtained using the GA-LMA fusion optimization algorithm.Moreover,the parameter variations of extended Debye model with different temperatures and moisture contents are analyzed.(3)Based on the parameterized model,the model branch characteristics are analyzed from the perspective of dielectric spectroscopy and power loss of model branch.Afterwards,the essence between the model parameters and frequency domain spectroscopy is discussed.Furthermore,the parameters to characterize the moisture content of insulation are excavated,which allows quantitative moisture assessment of bushing.(4)A new indicator-power loss density is proposed.Power loss analysis for capacitor voltage transformer and OIP condenser bushing is also carried out to study the relationship between the power loss density and distributed defects of insulation such as damping and aging.The research findings provide basis for effective evaluation of insulation conditions of capacitive equipment.