The Research On Temperature Characteristics Of Fiber Optic Voltage Transformers

Optical Fiber Voltage Transformer(OVT)is a voltage transformer for high voltage measurement of power grid.Its performance in many aspects is far superior to traditional electromagnetic voltage transformers,such as safety,measurement accuracy,dynamic range and so on.And OVT is a key part of the national smart grid construction.Although OVT has been proposed for decades,its temperature stability and other performance still do not meet the practical standards of the national grid.Therefore,a comprehensive and systematic research on the mechanism and temperature stability of OVT is very necessary.The main work of this paper can be divided into the following three parts:the theoretical basic research of OVT(the Pockels effect of electro-optical crystal),the development and production of dual optical path OVT,and the temperature characteristics analysis and experiment of OVT.Among them,the in-depth study of the theory of Pockels effect will have an important auxiliary role in the study of the temperature characteristics of OVT.The specific research contents are as follows:(1)For the lithium niobate crystal(LiNbO3,referred to as LN crystal),the transverse dielectric tensor and Pockels effect of LN crystals in any pass direction were studied in detail and intensively by quaternion,tensor matrix and other methods.From this,we obtained the polarization rotation axis of the LN crystal with different pass and applied voltage directions.Then,the influence of the polarization state of different input lights on the Pockels effect was studied.Finally,the correctness of the conclusion was verified by designing a large number of experiments,which laid the foundation for the later research.(2)The research and production of OVT has gone through the following processes:experiencing the optimal structure selection and verification of OVT,performance analysis and experiment of electro-optical crystal,annealing process discussion,mechanical design and improvement of related devices,strict component performance testing and other processes,and packaging process research.Finally,the fiber optic voltage transformer with dual optical path structure using BGO crystal was successfully developed.And under the high voltage DC electric field(0?6kV)and the high voltage AC electric field(0-2kV),the output parameter of OVT has a good linear relationship with the applied voltage.(3)The temperature characteristics of the developed OVT were studied in depth.This paper mainly analyzed the influence of the following factors on the temperature characteristics of the OVT:structural changes of the mechanical alignment of the sensor,crystal residual birefringence,thermal expansion of the crystal,thermo-optic effect and second-order nonlinear coefficient.In this process,a new method for measuring the residual birefringence of BGO crystals is proposed.At the same time,a measurement scheme which used F-B cavity for measuring the thermo-optic coefficient of BGO crystal is proposed as well.Then,the residual birefringence and thermo-optic coefficient of a series of BGO crystals were measured by setting up the corresponding experimental system.Finally,combined with the test of the temperature characteristics of OVT,the mechanism of the above factors in the temperature characteristics of OVT and the relationship between each parameter were obtained through analysis and research.57 figures,5 tables,50 references.