Research On High Precision Sensing Technology Of Electronic Current Transformer Based On Rogowski Coil

In recent years,the construction of smart grid and smart substation in China has been pushing forward in depth,which puts forward higher requirements for all kinds of basic measuring equipment.Current transformer is an important intermediate equipment connecting primary and secondary equipment.It is a key link for stable operation,correct monitoring and accurate measurement of power grid.The development of traditional electromagnetic current transformer is restricted by its large volume,heavy weight,difficult insulation and easy saturation.With its advantages of good insulation performance,small size and light weight,electronic transformers quickly occupy the market,which has aroused extensive attention and research by scholars.The commonly used electronic current transformers are optical current transformers and Rogowski coil current transformers.There are many structural links in optical current transformer system,and the complex fabrication process can not guarantee the accuracy of measurement.At the same time,it is easily affected by temperature,vibration and other factors,which can not guarantee the stability of long-term operation.This paper focuses on the sensor technology of electronic current transformer based on Rogowski coil.The main contents of this paper are as follows:In this paper,the sensing principle of the traditional Rogowski coil is introduced,and the frequency characteristics of the Rogowski coil are analyzed.The influence of different factors on the traditional Rogowski coil measurement is studied,and the corresponding mathematical model is established.The influence of the eccentricity of primary conductor and the change of ambient temperature on the coil measurement accuracy is analyzed,which lays a good foundation for the follow-up study.The biggest disadvantage of traditional Rogowski coil is that the manual winding is not uniform.Making Rogowski coil based on PCB board can solve this problem.In this paper,the combined Rogowski coil based on PCB board is studied,focusing on the method of increasing mutual inductance coefficient.The influence of eccentricity distance of primary conductor on the accuracy of coil measurement is analyzed,and the mathematical model of eccentricity distance and error is established.The simulation results show that when the eccentricity distance is 5 mm,the maximum error reaches 0.23%.Therefore,in the actual installation process,the eccentricity should be controlled within the allowable value as far as possible.The change of ambient temperature on the coil measurement accuracy is analyzed.The results show that the thermal expansion error factor of the whole PCB coil is equal to the thermal expansion coefficient of the skeleton when the skeleton expands.According to the skeleton thermal expansion coefficient,the error value can be calculated.In addition,according to the different directions of coil expansion,the relationship between the error and temperature is simulated.The results show that the error caused by coil expansion to the left is the smallest,and the error caused by coil expansion to the upper and lower directions is the largest.Traditional Rogowski coils and PCB Rogowski coils are closed-loop structures.In order to access the circuit conveniently,they are usually designed as clamp-like structures.However,the existence of clamp-shape structures will cause the measurement of coils to be affected by open air-gap.This paper analyses the relationship between the open air-gap and the error of the clamp-shape Rogowski coil,and proposes a clamp-shape Rogowski coil based on correcting PCB board.Through monitoring its output,the air-gap indication parameters are obtained.According to the fitting curve between the air-gap parameters and the output error,the output results can be automatically compensated.Finally,the electronic current transformer based on Rogowski coil is tested in laboratory.The test objects are flexible Rogowski coil and PCB Rogowski coils.As for the content of steady-state performance test,the errors between two Rogowski coils and traditional CT are tested in the current range of 5A～150A.The data trend of the measured current from 150 A to 5A is basically consistent with that when the current increases,which indicates that the measurement stability of Rogowski coils is better.Calibrating a conventional CT before testing can offset some of the error and set up a metal shield during the test to reduce the error.The measurement uncertainty of two Rogowski coils is tested.The test results show that when the measured current is maintained near a certain value,the measurement error remains basically unchanged,which indicates that the measurement stability of Rogowski coils is better.As for the content of transient performance test,the single-phase grounding short-circuit of power system is simulated in dynamic simulation laboratory.The test results show that the short-circuit current can be basically restored by either flexible Rogowski coil or PCB Rogowski coil.