Simulation Of Capacitive Voltage Transformer Model And Applications In Transmission Systems

With the improvement of grid complexity and scheduling requirements,various kinds of transmission system have been researched.In order to save non-renewable energy consumption,a lot of manpower material resources have been invested in our country to study new energy power generation system.At the same time,in order to meet the allocation of resources to the requirement of low loss large capacity transmission over a long distance,adding mixed reactive compensation of UHV transmission technology has also become a research direction of the electric power industry.As a voltage measurement indispensable equipment,capacitive voltage transformer(CVT)is very important in the novel transmission system.In order to solve the problem of CVT applied to the novel type of transmission system,in this paper,a novel CVT harmonic transmission model is established to measure harmonic under energy power generation system,a CVT transient model in the UHV transmission lines is equipped with hybrid reactive power compensation device of no-load switching-in,and a broadband equivalent model of CVT with the input and removal of the isolating switch and series compensation platform is established.To solve the problem of CVT harmonic measurement error and explosion appearing when the harmonic current increases,Y-? cascade equivalent conversion and transfer function method combining with Bode diagram are proposed to study the CVT harmonic transmission characteristics and the influence of stray capacitance and other main circuit parameters on CVT harmonic transfer function based on the MATLAB simulation.The results show that the bandpass feature presents in the lower frequencies of the Bode chart,and barely affected by the parameters.But because of the existence of the peak and trough,the corresponding harmonic measurements produce larger errors in the higher frequencies of the Bode diagram,in which the stray capacitance of compensation reactor and the stray capacitance of the primary side to the ground have a great effect on the harmonic transmission characteristics of CVT.Based on this,three methods are proposed to optimize the harmonic measurement.To solve the problem that in the UHV transmission system adding hybrid reactive compensation,the influence of closing the switch without load on the CVT secondary voltage,it is of great importance to research the cross-linking effect with UHV transmission lines and installations.In this paper,the influence hybrid reactive compensation installation exerts on the closing overvoltage and amplitude and frequency characteristics of CVT is researched.Then,an equivalent topology was established,and based on piecewise linear theory and Laplace transfomation,the oscillation frequency and attenuation coefficient of overvoltage are also calculated.Finally,with the change curve of hybrid reactive power compensation and closing phase,the change of low frequency voltage,fundamental voltage and peak overvoltage of CVT secondary circuit are also researched.The research results provide important references for the CVT transient questions of UHV power system hybrid reactive compensation and for the design and optimization of CVT damping device.To solve the problem that the disconnector operation of UHV series compensation platform may generate transient current and the transient voltage in the adjacent CVT,which may cause the damage of capacitive voltage divider,in this paper,a broadband equivalent model of CVT based on the method of "black box" and the principle of vector fitting method are established.The influence of all kinds of parameters on the CVT impedance frequency characteristics is also studied.Thenthe influence of inductance and resistance in series with the terminal of high voltage on the transient current suppression are compared.In this paper,the steady state model,the transient state model and the broadband model of CVT are established to get the rule of the comprehensive features,which provide a more perfect theoretical guidance for the application of CVT in novel transmission system and also provide a reference for CVT parameter optimization on the harmonic and ultra high voltage engineering.