Study On Measurement Error Characteristics Of High Voltage Capacitive Voltage Transformer

Capacitive voltage transformer(CVT)has the advantages of small size,light weight,low cost and can be used for carrier communication.It has gradually replaced the traditional electromagnetic voltage transformer(PT)and become the main voltage detection and metering device in the current high-voltage power system.However,due to its complex structure of partial pressure structure and electromagnetic unit(EMU),the steady-state measurement results are easily disturbed by external factors.In addition,compared with PT,the transient characteristics of CVT have been improved to some extent,but there are still serious transient problems due to the energy storage elements and transformers in its electromagnetic unit.Therefore,the steady-state and transient error characteristics of CVT still need to be further studied.In the analysis of steady-state error characteristics,the influence of stray capacitance on the voltage ratio difference(VDR)of CVT is analyzed by using the simple model of uniform distribution of stray capacitance,and the output voltage and error expressions of capacitor voltage divider(CVD)at different ground heights are derived.Then,in view of the fact that the stray capacitance is not evenly distributed,a calculation method of CVT stray capacitance and voltage distribution based on boundary element method is proposed.Secondly,the CVT model was built by Ansoft to compare the electric field distribution of the unshield and the applied shield,and verify that the shield can improve the electric field distribution of the CVT.Finally,Matlab genetic algorithm combining with Ansys APDL to optimize the size and position of the shield.After optimizing the internal field strength with the first-order optimization method inherent in Ansys APDL.The inhomogeneity k of field strength decreased from 8.13 of the initial parameter to 6.01,and the VDR decreased from 0.198%to 0.143%.After optimization with genetic algorithm,the field strength inhomogeneity k decreased from 8.13 to 4.689,and VDR decreased from 0.198%to 0.092%,with obvious optimization effect.In the analysis of transient error characteristics,the CVT transient simulation model was established by ATP-EMTP to analyze the CVT transient response and ferroresonance.For the CVT transient response,the influence of short circuit Angle,load capacity,connection mode,power factor,damping resistance and other factors on the transient response is simulated and analyzed.The simulation results are consistent with the theoretical analysis results.Ferromagnetic resonance,respectively for undamped and damping resistance for 2?,4?,5?,7?,9?,11?,13? simulation.Simulation results show that without damping,2?,4?,secondary voltage ferroresonance continued,5??13? cases,could be successfully damping ferroresonance,7??9? inhibition of ferromagnetic works best.The simulation results are basically the same as the actual damping resistance range.Considering transient response and ferro-resonance,model TYD110/0.01 H of CVT should chose 9? damping resistance.The steady state error and transient error characteristics of CVT are comprehensively analyzed in this paper,which can provide reference for the design,development and test of high-precision CVT.