Research Of Desiging And Optimizing Small Capacitance Capacitor Divider Electronic Voltage Transformer

With the development of smart substation, traditional voltage transformer is gradually replaced by electronic voltage transformers. In our country, electronic voltage transformers used in the high voltage grade are besed on capacitive voltage divider, the technology is mainly referenced from the traditional capacitor voltage transformer, especially using its capacitive voltage divider directly, leading the main electric capacity of electronic voltage transformer large, the capacitor of low voltage side is large too, and in the low voltage side there are all kinds of electronic components, these electronic components and the capacitor of low voltage side exist electrostatic and electromagnetic connections.When the power grid was impacted by transient voltage, amplitude of coupled to the low voltage side's overvoltage is large, which make the secondary system failure easily.There are roughly two kinds of solutions for the problem, one is to improve the anti-interference ability of the secondary system components.The second is to reduce main electric capacity of capacitor voltage divider, to reduce the strength of the interference. Based on the idea of reducing the main electric capacity of capacitive voltage divider, small capacitance electronic voltage transformer is studied in this paper.By using the combination of simulation and prototype test to study the small capacitance of electronic voltage transformer in this paper. Firstly analyzed factors that affects measurement accuracy of electronic voltage transformers with capacitor voltage divider, the ways to solve these influencing factors, in order to offer theoretical basis for effectively reducing the main electric capacity of capacitor voltage divider.Secondly, used Ansoft Maxwell software to establish finite element model of capacitive voltage divider, researched the effect of the external shielding on capacitive voltage divider measurement accuracy, and optimized its structure parameters. After optimized the structure parameters, four groups finite element model with different capacitance of capacitive voltage divider were established, solved different main electric capacitance of stray capacitance matrix, based on the regulation of IEC6044-7 standard for steady-state error, and determined the optimal value of capacitance for the capacitive voltage divider. Finally, researched the impact of change of the electric field around on the small electric capacitance of capacitor voltage divider's measurement accuracy. The results shows that reasonable design shielding can effectively reduce the influence of stray capacitance on the capacitor voltage divider; the radius of the outer ground ring and installation height are main structure parameters; by optimizing the structure parameters, the main electric capacitance of capacitive voltage divider of 500 p F measurement error is less than 0.1%; effects of the change of electric field around on the capacitor voltage divider's measurement accuracy is within the scope of the permit.According to the results of simulation, this paper has carried on the prototype development and testing, including situations with and without shielding ring, optimization of shielding ring, changeing angles of line and rated voltage, test results show that by reasonable design the structure of shieding ring, the ratio errors of the voltage transformer is about 0.004%, changing the lines' angle to simulate change of electric field, prototype's average ratio errors is 0.01%, change percentage of the rated voltage, the ratio errors and angle difference of the prototype is within the scope of the permit, the developed small capacitance electronic voltage transformer meets the design requirements of 0.2 level measurement accuracy.