Experimental Study Of Current Measuring System Based On Magneto-optical Isolator

Current transformers are the key equipment in power systems.They are important bridges and ties that connect the primary and secondary equipment.Therefore,the reliability and stability of current transformers and their measurement accuracy are more closely related to the safe and stable operation of smart grid.With the smart grid digital,network,the depth of information technology and IEC 61850 standard to promote and use,the traditional transformer limitations are increasingly significant,so the insulation is simple,dynamic range,wide frequency response optical current transformer(OTC)has been widely concerned by scholars.Especially in the context of smart grid and UHV construction,the research and use of optical current transformers will bring new changes to the whole power system.However,all aspects of optical current transformer research has gone through more than 30 years.So far,no mature products have been applied to the market.In the reason,there are still insurmountable defects in its performance.Such as temperature,birefringence,thermal stress on the measurement accuracy of the transformer interference.In addition,price costs and installation difficulties are also the main reason to limit the wide use of optical current transformers.Therefore,to explore the process more mature and more common material and the production cost is more expensive optical current transformer is particularly important.This paper focuses on the research of optical current transformers,and expounds the shortcomings of traditional current transformers and the limitations of them and the advantages and problems of optical current transformers,and points out the objective and subjective needs of the optical current transformer as the future research direction.Based on this,this paper introduces the principle and type of optical current transformer in detail,and further introduces the related devices such as magneto-optical isolator.In the case of expensive optical current transformer,difficult installation,low measurement accuracy and low speed,the paper puts forward some research ideas to explore new devices and solutions in other fields to greatly reduce the manufacturing cost and installation process.On the basis of fully comparing all kinds of magneto-optical devices,this paper chooses the magneto-optical isolator as the main research device and direction according to the new research ideas.According to the structure and characteristics of the magneto-optical isolator,an optical measuring circuit with magneto-optical isolator as sensor element is constructed.Then,the laser drive and transmitting unit,photoelectric conversion and receiving unit,AD sampling and transmission unit are designed.In order to meet the real-time requirements of the power system,this paper finally chose the FPGA with the faster operation and the richer internal resources as the main processor.According to the design requirements of FPGA,this paper builds FPGA-based hardware and software platform.At the same time,the interface design,board peripheral power supply design,bus design,AD sampling module design,DMA data storage module design and Ethernet design are carried out.At the end of this paper,the experimental platform of the whole optical current measurement system is designed to study the magnetic field measurement of the polarization-dependent magneto-optical isolator and the polarization-independent magneto-optical isolator.The relationship between the magnetic field and the voltage is plotted and the Isqcurvefit function is used to fit the magnetic field and the voltage nonlinearly.Experiments show that the two magneto-optical isolators have the conditions and characteristics in the field of magnetic field measurement and current measurement applications.This laid a solid foundation for the study of temperature,stress characteristics and the manufacture of actual products.