Study On State Detection Method And Device Design Of Capacitive Voltage Transformer

As a widely used transformer in power system,capacitive voltage transformer undertakes the function of voltage measurement and providing measurement signal.The accuracy of CVT secondary voltage signal directly affects power quality evaluation and accurate measurement.The component defects of CVT directly affect the accuracy of voltage measurement.The transmission characteristics of CVT also determine that it can not be used for harmonic voltage measurement.Therefore,the study of CVT state detection and harmonic measurement method has practical significance for power quality monitoring and power metering.In this paper,the structure model and working principle of CVT are analyzed.Five characteristic parameters of CVT are set: actual ratio,angle difference,upper and lower capacitance relative value,grounding current coefficient.Simulation model is established,and the sensitivity of response of characteristic parameters under different damage degree of internal components is analyzed.According to the changing rule of characteristic parameters,a method for judging the type of CVT defect is established.The mapping relationship between characteristic parameters and state types is established by using PNN neural network algorithm.The CVT state is correctly identified.The defect types of CVT capacitor,medium voltage transformer winding and compensation reactor are judged,and the accuracy of CVT measurement can be guaranteed by dealing with the defect in time.In this paper,the transmission characteristic curve of CVT is obtained by using the function method of impedance analysis with MATLAB software.Simulink model is built to simulate the transmission characteristic curve by applying harmonic source.The transmission characteristic shows that CVT can not be directly used for harmonic measurement.The relationship between the lower capacitor current and the harmonic content of the primary side voltage is studied.Based on this relationship,HCCR method for measuring the harmonic voltage of CVT is proposed and verified by simulation.The error of harmonic voltage measurement between traditional method and HCCR method is compared through simulation examples.The conclusion is that HCCR method can reduce the error of harmonic measurement of CVT,make CVT used in harmonic measurement,and provide accurate voltage signal for power metering.In this paper,CVT state detection and harmonic measurement method are studied,and a CVT detection device is designed.The device can detect the state of CVT and measure the harmonic voltage accurately.A test platform was built to verify the harmonic measurement function of CVT detection device.