The Electric Field Characteristics Simulation Of Converter Transformer Valve Side And Analysis Of Its Influence Factors

Relative to the AC transmission lines, the DC transmission has many advantages, such as big transmission energy, low cost, ensuring transmission quality at the greatest degree, durable and beneficial to the long distance transmission, there will be great developing prospects in future. Converter transformer is weak link in the process of the long-distance DC transmission system, compared to the ordinary transformer, it has to bear the DC voltage and polarity reversal voltage, and other kinds of voltage, so some insulation problems are easy to generate. In addition, due to the construction of the converter transformer is multifarious and the medium is complicated, to achieve the overall effect, we need do more unremitting efforts.In this thesis, the practical calculation model of the converter transformer is established, considering the electric field distribution characteristics of the valve side winding under the several voltages and mixed voltage are calculated and analyzed, and analyzing the impact factors in the process are also discussed.The model of transient electric field has been given and the transient electric field are simulated and calculated, during the polarity inversion process, the impact of the maximum field intensity to its valve side terminal position electric field is given in the condition of different length of the reversal time, the reversal time is set to sixty seconds, and the equipotential line distribution characteristics before inversion, inversion and after inversion are given, and the weak link of insulation of terminal position of the converter transformer has been found out.When the insulation medium is nonlinear, the maximum field intensity value and equipotential line distribution are given, two factors of the nonlinearity which is influenced by the insulation medium resistivity are researched respectively, the two factors are the electric field intensity and temperature, the equipotential line distribution of the converter transformer is given under the influence of the electric field intensity and temperature. Isotropy and anisotropy of the insulation medium are compared, the difference between isotropy and anisotropy is obtained, the reasons of the differences are analyzed, and the electric influence trend on the role of the initial value of the resistivity is given.Under the polarity reversed voltage, the maximum of the electric field intensity of insulation medium and the potential distribution before and after the first polarity reversal are given, the characteristics of the electric field distribution in the oil-paper insulation medium isotropic and anisotropic case before and after the first polarity reversal are also studied, further on the basement of considering the nonlinear of insulation medium, the electric field of converter transformer valve side is numerical computed, and a comparison of isotropic and linear, isotropic and nonlinear, anisotropic and linear, anisotropic and nonlinear four kinds of calculation results before and after the first polarity reversal, obtaining factors of variation and influence of the electric field distribution, it’s provided a theoretical reference for the manufacture of converter transformers.