Research On The On-line Calibration And Traceability Method Of Electronic Current Transformer

As a new generation of current signal acquisition core equipment,the electronic current transformer is widely consumed in smart substations,and its accuracy is crucial to the fairness and justice of electric energy metering.According to China’s metrology technology regulations,electric energy measurement instruments shall regularly exercise calibrations to ensure their measurement accuracy.Traditional electronic current transformer calibration usually implements an off-line calibration method,that calibration process requires power failure,usually once every 10 years.The electronic current transformer contains a large number of electronic components in the signal conversion and acquisition link,and its reliability and stability are lower than that of the traditional electromagnetic current transformer,and the calibration period is much shorter.If referring to electronic equipment（such as electric energy meters）,assuming that the calibration cycle of electronic current transformers is once every two years,the calibration workload will be 5 times that of traditional electromagnetic current transformers.But limited by the requirements of stable operation of the power grid,it’s impossible to schedule a power outage in such a short period for offline calibration.Therefore,it is urgent to study the on-line calibration method of electronic current transformers to improve calibration efficiency.At the same time,to ensure the uniformity and comparability of the calibration data of electronic current transformers,it is necessary to solve the traceability problem of electronic current transformers and establish a complete calibration chain of electronic current transformers so that their values can be traced to the national primary standard.The current research on the calibration and traceability technology of electronic current transformers cannot meet the actual needs of grid energy metering.For this reason,this paper has carried out a systematic research,and the main work is as follows:Aiming at the on-line calibration of GIS electronic current transformers,which are widely used at present,a scheme based on the all-optical current transformer（FOCT）as the standard current transformer was proposed.In order to solve the problem of low accuracy of the existing FOCT,the differential element method was used to establish the FOCT rotating fiber polarization state change mechanism model.The model was used to simulate and guide the development of FOCT with high circularity coefficient.Basic accuracy test,short-term measurement stability test,FOCT winding error test,verify the correctness of the model.In order to realize the long-term state assessment of the measurement error of the electronic current transformer,an error prediction method based on BP neural network was proposed.According to the analysis of the key factors affecting the error of the typical electronic current transformer,a long-term live evaluation platform under a typical environment was established and algorithm research was carried out.The data shows that when the relative error between the predicted value and the actual value is within 20%,the prediction accuracy of the algorithm is higher than 90%,which proves the effectiveness of the method.In order to solve the key problem of the establishment of the electronic current transformer value traceability system——IEC 61850 digital value traceability,a traceability method based on the synchronous pulse source was proposed,which realizes the accurate synchronization control of the standard digital source and the standard synchronous pulse source.The developed electronic transformer standard device has a ratio difference measurement uncertainty of5.0×10^-5 and a phase difference measurement uncertainty of 0.13′,which preliminarily verifies the method’s feasibility.On this basis,in order to meet the traceability needs of electronic current transformers with a higher accuracy class,a high-accuracy differential digital source synthesis algorithm based on quantum voltage was proposed,which solves the problem of traceability and low accuracy of digital source.Simulations and experiments have shown that the use of the above algorithm can increase the existing traceability uncertainty level by 5 times,realize the traceability of the digital source to the quantum voltage,and provide a foundation for establishing the traceability system of electronic current transformer based on quantum voltage.