Research On Measurement Accuracy Of Fiber-Optical Current Transformer

As one of the special plans of the State Grid Corporation of China’s 12 th Five-Year Development Plan,fiber-optical current transformers have the advantages of large dynamic range,fast dynamic response,and good electromagnetic interference resistance.However,they have been difficult to be put into practical use on a large scale so far.The main reason is It is the measurement accuracy of the fiber-optical current transformer.The measurement accuracy of fiber-optical current transformer refers to the current error of the transformer when measuring the primary current,and its performance indicators such as basic accuracy and harmonic accuracy are specified in the standard.In actual operation,the measurement accuracy of fiberoptical current transformers will be affected by factors such as temperature,linear birefringence,random noise,harmonics in the power grid,etc.,and measurement inaccuracy may occur,which will cause damage to the measurement and protection of the power system.Serious impact.Therefore,study the measurement accuracy characteristics of the fiber-optical current transformer,analyze its influencing factors,and propose error compensation measures for the inherent zero bias error of the transformer,which is important for ensuring the normal operation of the measurement and protection functions of the fiber-optical current transformer and promoting the fiber-optical current transformer.The large-scale practicality of the company is of great significance.Existing researches on the measurement accuracy of fiber-optical current transformers mostly focus on the impact of single factors such as the temperature of the transformer,linear birefringence effect,and random noise.There is a lack of multi-factor effects on the measurement accuracy of the transformer(temperature,random Noise,linear birefringence,internal optical device characteristics,etc.),and the measurement accuracy of the transformer is affected by the coupling of multiple factors.It is not enough to consider the influence of a single factor.This paper takes the fiber-optical current transformer as the research object,and carries out theoretical,simulation,and experimental research on the basic accuracy,harmonic accuracy and its influencing factors.First,based on the working principle of the fiber-optical current transformer,a closed-loop system model of the transformer is established,and the error sources of the fiber-optical current transformer are systematically analyzed.The main error sources are optical path system error,random noise error,and circuit error.The optical path system error is mainly affected by the characteristics of the internal optical device and the temperature.The random noise error mainly comes from the noise introduced by the optoelectronic device,and both of them mainly affect the basic accuracy of the fiber-optical current transformer.The circuit error comes from the signal attenuation introduced by each link during signal processing,which mainly affects the harmonic accuracy of the fiber-optical current transformer.Secondly,the calculation analysis and influencing factors of the basic accuracy and harmonic accuracy of the fiber-optical current transformer are carried out.The basic accuracy of the transformer is studied from the two aspects of optical path system error and random noise error.Through theoretical derivation and drawing contour diagrams,the polarizer,phase modulator,quarter wave plate,sensor are quantitatively studied.The influence of optical fiber characteristics and ambient temperature on the optical path system error,as well as the influence of modulation phase,counting bandwidth and primary current on random noise error,puts forward the basic accuracy calculation formula of fiber-optical current transformer.Based on the closed-loop dynamic model and transfer function of the fiber-optical current transformer,the amplitude-frequency characteristics of the transformer system are analyzed,and the calculation formula for the harmonic accuracy of the fiber-optical current transformer is proposed,and further quantitatively analyzes the influence of the preamplifier magnification and the number of A/D conversion bits on the harmonic accuracy of the transformer.Finally,an fiber-optical current transformer measurement accuracy experimental platform was designed and built.The basic accuracy and harmonic accuracy of the fiber-optical current transformer prototype were performed according to the test method specified in the standard.The measurement accuracy of the fiber-optical current transformer varies with the current.Changes in amplitude,frequency,and superimposed harmonics.The comparison between the experimental results and the theoretical calculations shows that the two trends are consistent,which verifies the accuracy of the theoretical analysis.In addition,the bias error of the fiberoptical current transformer is measured based on the experimental platform,and its influence on the ratio difference when the transformer measures small currents is analyzed.Based on the adaptive filtering method,an adaptive error compensation system for fiber-optical current transformer is proposed and the error compensation analysis is carried out through simulation.The simulation results show that the adaptive error compensation system can compensate the zero-bias error very well,so that the measurement ratio difference is greatly reduced,and it meets the 0.2-level accuracy requirement of the transformer.