Numerical Analysis And Experimental Verification Of The Effect Of Ambient Electric Field On The Error Characteristic Of Capacitive Voltage Transformer

Capacitor voltage transformer(CVT)is the most common voltage transformer in the power system,which is usually installed in the substation.The power equipment installed around CVT has the characteristics of complex structure,centralized layout,wide distribution and different electrification conditions.As the voltage increases and the equipment capacity increases,the operation environment of CVT becomes more complex,resulting in the increasing influence of environmental electric field on the measurement characteristics of CVT.The traditional off-line calibration method can not measure the online operation error of transformer caused by electromagnetic environment,which makes it urgent to evaluate the influence of the environmental electromagnetic field on the error characteristics of the power transformer from the aspects of mechanism analysis and numerical calculation.The main contents and innovative achievements of this dissertation are as follows:Firstly,the finite element model of CVT is established.The structure of the capacitive voltage divider is simplified to a 20-layer series plate capacitor,and the structure of the external ceramic sleeve is simplified to a smooth cylinder.Compared with the calculation results of the equivalent model and the actual model,and the relative difference between the simplified ceramic casing and the actual casing is ± 0.1%,the conclusion shows that the equivalent model can effectively reflect the real working state of CVT.Secondly,in view of the characteristics of large size,high aspect ratio and difficult numerical modeling of power equipment,the grid generation method and the setting of calculation domain are optimized.When calculating the error characteristics of CVT,the method of multi-layer partition is used to optimize the grid,and a calculation domain is set to reflect electric field distribution in the distance of the model,the outer calculation domain of the reference model is set to be the same size as that of the original model to reduce the error.Through the analysis of the multi-layer plate model similar to the size and operating principle of CVT,it is found that these optimization calculation methods for mesh generation and calculation domain settings can greatly improve the calculation efficiency while ensuring the calculation accuracy.Thirdly,the finite element model of typical power equipment,including arrester and disconnector,is established by Maxwell to calculate the influence of environmental electric field on the measurement characteristics of CVT with different voltage levels.The analysis shows that the environmental electric field mainly changes the ratio difference of CVT by causing the change of stray capacitance,and the ratio difference approaches 0 with the increase of equipment spacing.Equipment with different potential distribution has different effects on CVT error characteristics.The influence of metal bracket on the ratio difference of CVT is greater than that of arrester.The effect of the closing state of the disconnector on the CVT ratio difference is greater than that of the open state.The higher the voltage level is,the greater the CVT ratio difference is affected by the environmental electric field.The larger the angle and the smaller the diameter of the high voltage lead,the smaller the CVT ratio difference.Interphase interference will lead to the negative deviation of CVT ratio difference,and the middle-phase CVT ratio difference is most affected.The CVT error characteristic is the result of the coupling effect of multiple influencing factors.When analyzing the difference of CVT ratio,the overall consideration should be taken into consideration with the actual situation.Finally,an experimental scheme is designed to measure the off-line measurement error of CVT by using the difference method,so as to investigate the variation trend and degree of CVT measurement error caused by different variables.Comparing the experimental results with the simulation results,it is found that the trend and degree of the influence of the external electric field of the experiment and the finite element analysis on CVT are basically consistent,which verifies the rationality and accuracy of the numerical analysis modeling method and the calculation results.