Optimum Design Of Fiber Optic Current Transformer For Ships

Since the 1980 s,with the development of large-scale,informatization,and intelligent naval ships,a new integrated power system(IPS)has been proposed.The current transformer can cooperate with the relay device and provide signals to the relay device to cut off the fault circuit to protect the safety of the power supply system when a short circuit,overload or other fault occurs on the line,which is an important part of the comprehensive protection link of the IPS power control module.However,the IPS adopts an all-electric-driven overall design,which has a larger measurement range and a higher requirement for the volume of the current transformer.Therefore,the traditional electromagnetic current transformer is no longer suitable.The Fiber-Optic Current Transformer(FOCT)is designed based on the Faraday effect and uses optical fiber as the sensing medium.The FOCT,which has good insulation,high reliability,fast response,large measuring range,small size,light weight,green environmental protection and other advantages,is the best choices for current transformers used in ships.However,the current research on all-fiber current transformers is mainly focused on the field of power systems.Therefore,considering the special conditions of use of ships,studying FOCT for ships is of great significance.This dissertation summarizes the current research status of all-optical current transformers and optical current transformers used in ships,and optimizes the FOCT vibration problems,dynamic characteristics and inhomogeneous magnetic fields for ships,including the following aspects:(1)Taking the anti-vibration performance as the main consideration,the optical path structure scheme of shipboard FOCT is selected and an optimization scheme is proposed.Firstly,using the Jones matrix,we have established the optical transmission models of FOCT polarization characteristics of the three main structures of the current Sagnac type,Y-waveguide collinear type,and straight-waveguide collinear type;then,compare the anti-vibration performance of the three,find Sagnac type has better resistance to line vibration,and the collinear anti-angle vibration capability is better.Finally,in combination with the actual vibration conditions on the ship,the straight waveguide colinear type is selected as the all-fiber current transformer solution for ships,and it is also proposed to pass the reduction.The small delay loop length method improves the anti-vibration performance of the FOCT,and attention should be paid to the anti-vibration measures that take the same intensity in the horizontal and vertical directions of the FOCT during the installation process.(2)FOCT system modeling and design.First,FOCT closed-loop modulation and demodulation scheme is introduced in detail on the basis of the straight-line colinear optical path structure.The closed-loop pulse transfer function of the system is derived;then,based on step response and closed-loop amplitude characteristics,system simulation and parameter optimization are performed;Finally,based on the optimization results,the appropriate device was selected to design the hardware circuit and FPGA program of the shipboard FOCT signal processing module.(3)Establish a sensing fiber loop distribution paramete r model to analyze the effect of non-uniform magnetic field caused by conductor eccentricity on FOCT.Firstly,considering the effect of linear birefringence and inhomogeneous magnetic field on the sensing fiber ring,a sensing parameter distribution model of the sensing fiber ring that is more in line with the actual situation is established;then,considering the influence of the shape and size of the current-carrying wire on the magnetic field distribution,The centroid equivalent replaces the current-carrying conductor.The influence of the non-uniform magnetic field caused by the eccentricity of the current-carrying conductor on the FOCT output is analyzed.Finally,the distribution parameter model and the eccentricity problem are simulated and analyzed.The results show that when the current-carrying conductor deviates from the center of the circle,the FOCT ratio difference is equivalent to adding an eccentricity ratio difference on the basis of the standard ratio difference.The eccentricity ratio difference is related to the linear birefringence size,the number of sensor ring turns and the eccentricity.In the field installation,attention should be paid to reducing the eccentric distance of the current-carrying conductors,and the requirements for small angles can be relaxed.(4)The ship FOCT prototype was designed based on the straight waveguide collinear optical path structure and the closed-loop modulation and demodulation scheme,and the performance of the prototype was tested.The basic paramet er test experiment,vibration experiment and dynamic characteristic experiment and conductor eccentricity experiment were carried out respectively.The experimental results show that the prototype can realize the basic function of measuring current.It can achieve 0.2 grade accuracy when measuring large current.It also has good linearity and anti-vibration performance.The transit time is ?=1.40?s and the response time is 70?s,the sampling delay is 120?s.In addition,the change in eccentric angle of the current-carrying conductor has little effect on the FOCT output.