Design Of All Fiber Current Transformer Based On Spatial Nonreciprocal Phase Modulation

In recent years,with the rapid development of power systems,the tolerance of power transmission has increased,traditional electromagnetic current transformers are unable to meet the requirements of today’s power system.From the aspects of safety,market efficiency and low carbon environmental protection,current sensors will tend to be more efficient,reliable and miniaturized.All-fiber current transformers are a product that meets current market requirements and the trend of the times.This paper focuses on designing a new structure of phase modulation for all-fiber current transformers and fiber optic gyroscopes,combined with the characteristics of the devices,a spatial non-reciprocal phase modulation method is proposed,which eliminates the limitation of the eigenfrequency on the system in principle.And at the same time designs and completes the prototype,verify the correctness of the theory through experiments,and verify the reliability and accuracy of the system.The main contents of the paper are as follows:First,the spatial phase modulator and the reflective all-fiber current transformer under the modulation method are analyzed in detail.The matrix model and theoretical output model of the optical path are established according to the index ellipsoid and Jones matrix,which lays the theoretical basis for the following.Secondly,two spatial phase modulation methods,open-loop design and closed-loop design,are proposed.By analyzing the lateral electro-optic effect of each tangential lithium niobate crystal,the design scheme is finally selected.The phase modulator design is completed and experiments are carried out to verify the generation of differential phase.Thirdly,complete the prototype of the current transformer from the application point of view,write the host computer program through LabVIEW,design the closed loop feedback structure.And experimental analysis of first-order closed-loop feedback(phase-locked)and second-order closed-loop feedback(lock-modulated voltage),verify the correctness of the structure.Finally,the current transformer principle prototype of the spatial phase modulation is tested.The experimental results show that the open-loop structural transformers change linearly when it is affected by the environment,combined with error compensation technology,the minimum ratio error is less than 0.02%.The closed-loop structure transformer has good detection consistency in the rated current range of 15~1800A(1%~120%).Within the rated measurement range,the transformer ratio error meets the error limit of the special purpose current transformer in the national standard,and the measurement accuracy reaches 0.2S.