Research On Transient Error Characteristics Of Capacitor Voltage Transformer

Capacitive voltage transformers(CVT)are widely used in high voltage power grids because of their excellent performance.Compared with the traditional electromagnetic voltage transformers,the structure of CVT is more complex,and its measurement error is easily affected by the environment and other factors.Because CVT contains more energy storage and nonlinear components,when the system failure,CVT will also appear more serious transient problems,threatening the safety and stability of the power system.Therefore,studying the transient error characteristics of CVT and improving the transient characteristics of CVT are not only of practical value to the design of CVT products,but also of great significance to the maintenance of the safety and stability of the power system.Firstly,the basic principle of CVT is introduced in detail,and the steady-state measurement error theory of CVT is comprehensively expounded.The influence of the surrounding electric field on the steady-state error of CVT is analyzed emphatically by using the Bode diagram.The results show that the stray capacitance near the power frequency can cause the steady-state error,but the stray capacitance has little effect on the steady-state error.Then,the basic principles of the transient response and ferroresonance of CVT are analyzed,and illustrated by simple simulation.The results show that the secondary voltage of CVT cannot accurately reflect the primary voltage when the CVT is in the state of transient response and ferroresonance.Secondly,a simulation model of CVT transient response was built according to the electrical structure of CVT,and the influence of CVT on relay protection was simply analyzed.On this basis,the maximum transient error and attenuation time were proposed to measure the transient error of CVT,and the circuit parameters needed for simulation were calculated and selected.Simulation analysis of the parameters of the equivalent capacitance and the parameters of the damper,and the load parameters of main circuit parameters on the effect of CVT transient error,and by using entropy value method to calculate the effect of main circuit parameters of CVT transient error weights,the results of simulation and entropy value method results show that the circuit parameters within a reasonable range,the equivalent capacitance C_e,the most profound effect on the maximum transient error Secondly,the influence of power factor cosφ,damping capacitance C_f,damping resistance R_f and load capacity S on the maximum transient error decreases successively.The damping capacitance C_f has the greatest influence on the attenuation time of transient error,followed by damping resistance R_f,power factor cosφ,equivalent capacitance C_e and load capacity S.Then transformation method is used to collect the CVT intermediate transformer excitation characteristic curve,set the CVT ferro-resonance simulation model,analyses the inspire moments and resonant type damper parameters influence on CVT ferroresonance,results show that compared with the secondary side voltage zero short-circuit,secondary side voltage peak of short circuit,the ferromagnetic resonance excitation is more serious;When the damping resistance is 8Ω,the suppression effect of CVT ferroresonance is the best.The simulation results verify the theoretical value of the CVT damping resistance and the rated value of the actual product.Finally,the transient error correction method based on virtual CVT is used to correct the transient error of CVT,and the proposed method is simulated and verified according to the transient response simulation model of CVT.The results show that the corrected primary voltage can fit the actual primary voltage well,which verifies the effectiveness of the above correction method.