| As a very important electrical equipment in the power system,high voltage bushings are mainly used for the insulation of the inlet and outlet lines of transformers,reactors,circuit breakers and other power equipment and high voltage circuits through walls.Due to the wide variety of high-voltage bushings,considering the current high-voltage bushings in operation,OIP condenser bushings account for a relatively large proportion,about 80%.Therefore,OIP condenser bushings are taken as typical research objects in this paper.Taking into account the effects of temperature and moisture on the dielectric properties of the capacitor core and the enhancement effect of the skin effect on the harmonic losses of the loading conductor,the power loss characteristics of the capacitor core and the current-carrying structure of the bushing under harmonic voltage and current are studied separately.At the same time,the electro-thermal-moisture distribution coupling model of the bushing was established to obtain the coupling relationship between the electric field,the temperature field distribution and the moisture distribution.Taking into account the non-linear characteristics of the capacitor core dielectric parameters and thermophysical parameters,the coupling characteristics of the electro-thermal-moisture distribution of the bushing under harmonic voltage and current were studied.The research results of the thesis are as follows:(1)Considering the effect of temperature and moisture content on the dielectric loss of the bushing under harmonic voltage,the test bushing model is designed according to the actual structure of the bushing,and the frequency domain dielectric spectrums of the bushings under different temperatures and moisture contents are measured through artificial moisture simulation tests and dielectric response tests.Based on the dielectric characteristics,considering the enhancement effect of the harmonic voltage on the dielectric loss,a HVDC transmission system was built.The harmonic voltage generated by the converter valve is used to calculate and analyze the dielectric loss of the bushing and its change law with temperature and moisture contents.An index of dielectric loss enhancement coefficient is used to characterize the harmonic voltage components impact on dielectric loss.(2)Taking into account the enhancement effect of skin effect,a calculation model of the active power loss of the bushing loading structure under harmonic current is established,and the calculation of the active power loss of the bushing loading structure is studied from the theoretical analysis and experimental verification method;Based on the simulation of the current waveform of the loading structure of the converter bushing,the quantitative calculation of the active power loss of the bushing loading structure is carried out,and an enhancement factor considering the skin effect on the active power loss of the bushing loading structure under harmonic current is proposed to correct its value of the active power loss.(3)The coupling characteristics of the electro-thermal-moisture distribution under harmonic voltage and current are studied from three aspects: the establishment of a coupled model of electro-thermal-moisture distribution,the measurement of the nonlinear characteristics of the parameters of capacitor core,and the finite element simulation analysis of bushing under harmonic voltage and current.Based on the electro-thermal coupling of the bushing and the heat and mass transfer theory of porous media,a electro-thermal-moisture distribution coupling model was established to obtain the coupling relationship between the electric field,temperature field distribution and moisture distribution of the bushing;The finite element simulation software is used to establish a finite element bushing simulation model,and the nonlinear characteristics of the capacitor core dielectric parameters and thermophysical parameters and the characteristics of harmonic voltage are incorporated.The electric field,temperature field,dielectric loss density field distribution and moisture distribution of the bushing are obtained by simulation and the influence of the nonlinear characteristics of the capacitor core parameters,the dielectric loss,harmonic voltage and initial moisture content of the oil-impregnated paper on the temperature field distribution and the moisture distribution is analyzed. |
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