Research On Harmonic Transmission Characteristics And Measurement Methods Of Capacitor Voltage Transformer

With the construction of my country’s converter stations and UHV DC transmission projects and the integration of a large number of new energy projects,many non-linear devices such as switching power supplies and semiconductor components have been widely used in the power grid.Although these devices have improved distributed energy However,it also injects a large number of harmonic sources into the power system.At present,the measurement method of capacitive voltage transformer（CVT）cannot accurately obtain the harmonic content in the power grid.Accurate and effective harmonic measurement is an important basis for mastering the harmonic status of the power grid,carrying out harmonic control,and improving power quality.This article first established its broadband equivalent model based on the actual physical structure of the CVT.By controlling a single variable,the gradient simulation experiment was carried out one by one for each distribution parameter in the model that has an impact on the harmonic transmission characteristics of the CVT broadband model.The result of the parameter’s influence on the transfer characteristics.Aiming at the problem that CVT cannot obtain accurate harmonic content,a capacitive current method is proposed in which a high-precision current transformer is installed on the CVT voltage divider capacitor to measure harmonics.Through simulation and actual physical experiments,the simulation and experimental results are compared.A comparative analysis has verified the effectiveness of the method.In the simulation process,the influence of the key factors,namely the capacitance value and the measurement accuracy of the current transformer,on the harmonic voltage measurement error of the capacitive current method is analyzed.For the convenience and effectiveness of the measurement,a method of adding a measuring terminal C₃ to the CVT for harmonic measurement is also proposed.The influence of the measurement of the capacitance value of the capacitor C₃ on the measurement of the harmonic content is analyzed,and finally the simulation results are analyzed.Comparing with the actual physical test results,it verifies the feasibility of harmonic monitoring by measuring capacitance C₃.Both methods can accurately and effectively measure the harmonic content in the power grid,and are simple to operate and convenient to measure,and have good engineering application value.