| In the modern society with the rapid development of science and technology,the application of new energy is expanding day by day,the load of users is diversifying day by day,and the use of high-power power power electronic equipment is expanding day by day.All of these three will inject harmonic pollution into the power system,which not only reduces the quality of power supply,but also damages the production equipment of the power system.At the same time,social production also puts forward higher requirements for power quality such as power grid frequency,voltage waveform,etc.To solve the harmonic problem,the first thing to solve is how to measure the accurate harmonic voltage.Capacitor voltage transformer(CVT)plays a dominant role in high voltage measurement of power system.At present,CVT has fully met the requirements of fundamental voltage measurement and fundamental signal transformation of relay protection device in high voltage power grid.However,in the system with harmonic component,CVT can not correctly reflect the actual situation.Because CVT is based on the working principle of resonance measurement,there is a large measurement error in the measurement of harmonic voltage signal.In other words,CVT can not be used for harmonic measurement,which limits the application range of the equipment.In order to use CVT to measure harmonic voltage accurately,this paper presents a correction measurement method which only uses the secondary side output voltage signal of CVT as the original data to calculate the value of the primary side harmonic voltage.In the first chapter,the background and significance of the correction curve of CVT Based harmonic voltage measurement are described,and the research status of CVT harmonic measurement at home and abroad is introduced.In the second chapter,the basic components of CVT are analyzed and summarized,the model of CVT is established,and the characteristics of each component are analyzed theoretically.In the third chapter,the influence of CVT equivalent circuit structure parameters on the transmission characteristics is introduced through theoretical analysis,derivation and simulation calculation,so as to solve the deviation correction problem of the transmission ratio and phase-shift characteristics caused by parameter changes.In the fourth chapter,the model simulation method is used to study the harmonic transmission characteristics of CVT,and the theoretical analysis results and simulation calculation are compared.In Chapter 5,the preparation method of CVT harmonic measurement error correction curve is introduced.In this paper,CVT is used as a breakthrough point to solve the problem of how to use the existing power grid equipment to accurately measure the harmonic voltage.Firstly,the equivalent circuit of CVT is established according to the classical circuit theory and the actual structure of CVT,and the amplitude frequency response curve of CVT is drawn according to the two port network theory.Then the voltage value of each harmonic in the output signal of the second side is calculated by using the fast Fourier transform tool.The numerical relationship between the fundamental wave and each harmonic in the amplitude frequency response curve of CVT is calculated by computer,and the harmonic voltage value obtained by correcting the secondary side is calculated.Finally,the actual value of the first harmonic voltage is obtained,and the purpose of using CVT to accurately measure the harmonic voltage is realized. |
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