Theoretical And Technical Research On A Terfenol-D And Optical Bragg Grating Based Current Sensor

With the rapid development of the market-oriented process in powerindustry, the high technology of current sensor, which plays an important role inthe measurement and relay protection in power industry, is being demandedincreasingly. At present, the commonly-applied current sensor, which is based onelectromagnetic induction principle, has such problems as saturatedmagnetization, ferromagnetic resonance, narrow frequency band, small dynamicrange, inflammability and explosibility etc.. These problems are more prominentand the manufacturing cost is also more and more expensive along with theupgrade of voltage. With the advantages of good insulating property,electromagnetic interference immunity and wide frequency band, greatachievements have been made in the optical current sensor research andapplication for recent years. However, the scheme of Faraday magneto-opticaleffect current sensor is still subjected to the factors, such as fiber linearbirefringence and ambient temperature. There are no better solutions to powersupply by the electronic circuit in electropositive potential and electronic circuitreliability of the photo-electricity compound scheme. The emergence of thefiber Bragg grating(FBG) may provide the new way to solve the problemeffectively.As a result of research and development in recent years, the technique ofFBG sensor has become the most reliable and practical sensor technique amongfiber sensors. With the advantages of wavelength encoding, compatibility withfiber and distributed measurement system realization, FBG has been widelyapplied in the strain and temperature measurement in engineeringstructures. The giant magnetostrictive material(GMM) is a kind of newmagneto-mechanical converting material and has been broadly applied in theresearch field of energy exchanging and driving due to its advantages of largeflexible coefficient, high electromechanical coupling coefficient and shortresponse time etc.. AC current sensor method of combining GMM with FBG isput forward in the paper, and thus, the measurement of AC current signal iscarried out by using coarse wavelength division multiplexer(CWDM) filter edge to demodulate the alternating strain caused wavelength shift in the fiber.The paper indicates that the dynamic sensing model of using GMM asactuating system is built by using Jiles-Atherton model of ferromagnetic material,quadratic domain model and piezomagnetic equation, and that the actuatingcharacter of GMM is simulated and analyzed in the condition of AC currentmutual-inductance. On the basis of the hysteresis dynamic sensor model of GMMand strain sensor theory of fiber grating, the AC current sensor theory ofcombining GMM with FBG is built, and the numerical relation between theexciting current and wavelength shifting of FBG is determined.Based on wavelength encoding character of FBG, by using CWDM filteredge demodulation scheme and the linear relation between transmittivity ofCWDM and wavelength, the demodulator that can be used for FBG alternatestrain signal demodulation is developed, which makes CWDM becomedemodulation tool of AC signal and solves the wavelength informationdemodulation problem of alternate current sensor. The related character ofmagnetic field intensity of AC current, GMM strain and wavelength shifting isobtained by using GMM rod, FBG, solenoid and CWDM composing experimentsystem of current sensor.In the paper, magnetic circuit system, composed of magnetic material,GMM rod and permanent-magnet material, is optimized by using numericanalysis method; the measurement range of current measuring in sensing systemis defined by adjusting air gap of magnetic circuit; the static bias of the sensor isdefined by adjusting the charge magnetism direction dimension of permanent-magnet material. The axial stress kinetic model of GMM rod in magnetic circuitis built and amplitude-frequency characteristic of GMM is analyzed by usingnumeric simulation technique, which has optimized the character dimension ofGMM rod and verified the rationality of its structure through simulation andexperiment.Furthermore, one kind of optical current transformer applied in powersystem is developed in the paper. Under the condition of with and without biasmagnetic field, the detection of power AC current signal is carried out by usingfiber grating demodulation technique of CWDM. The output-signal quality isassessed and harmonic component of the sensor output signal in different output areas is analyzed by using Fourier transform. The system transfer function withhysteresis character is fitted by using high-order function group. For thedeformation of the sensor output-signal in different output areas, we put forwardthe scheme of restored the measured current true wavelength by using output-signal, which carries out the rebuilding of the input-signal. This optical currenttransformer has advantages of simple structure, good stability, precisemeasurement, so it may become a choice of current measurement in electricpower system.