Study Of GMM-FBG Current Transformer Based On DFB Laser Demodulation Technology

Fiber Bragg grating sensing technology is the highest reliable and most practicaloptic sensing technology with wavelength division multiplexing. Terfenol-D is a newtype of giant-magnetostrictive material (Giant Magnetostrictive Material, GMM), thestretching coefficient of the Terfenol-D is several times higher than ordinarymagnetostrictive material, with a response time of less than1με, the temperatureapplications range is wider than the piezoelectric ceramics (PZT). The combinationof FBG and GMM may be a new option for optic current transformer.This paper studies a kind of current transformer based on FBG and GMM, themeasurement of the current is transformed into the measurement of the magneticfield. FBG was boned to GMM with self-formulated resin adhesive, which was usedas the sensor probe of the current transformer, the magnetic circuit composed offerrite materials with good high-frequency performance is used to constrain andguide the magnetic field into the sensor probe. Since the FBG is wavelength encodeddevice, the current is measured by the FBG demodulation system.The measurement accuracy of the current transformer is affected by non-linearity and hysteresis characteristics of GMM, and the application and developmentof fiber grating current transformer is limited by the FBG demodulation technique.For the above-mentioned disadvantages of the current transformer, a quadraturedemodulation method based on narrow-band distributed feedback laser (DFB) isproposed in this paper, the laser acted as both the light source and a demodulationdevice, the narrow linewidth characteristic is used to achieve high-precisionwavelength demodulation of FBG. By utilizing a small range of GMM material andFBG sideband, we realize the current sensing and demodulation, reduce the effect ofthe hysteristic and nonlinear characteristics of GMM with maximum limit, improvethe measurement accuracy while taking into account the dynamic measurable range.Fiber Bragg grating is cross-sensitive to strain and temperature, the paper propose a quadrature point locking method based on the wavelength tuningcharacteristics of DFB laser to compensate the effection of temperature for currenttransformer. The quadrature point position will change when the fiber grating isaffected by temperature drift, the quadrature point is locked by tuing the centralwavelength of DFB laser and using the adaptive control algorithm, the temperaturecompensation of FBG current transformer is realized and at the same the temperatureinformation is achived.This paper studies the frequency response of the current transformer, bysimulation analysis and experiments, we achieve the intrinsic frequency of the GMMrod based on the optimization of the GMM structure size. The output characteristicsof the current transformer is discussed in the paper under different frequency excitingcurrent, determine the measurement bandwidth of the current transformer, and whichprovides a theoretical basis for the measurement of high-frequency current and high-frequency noise monitoring.The fiber grating current transformer may become a new option for currentdetection in power system, which has the advangtage of simple structure, highprecision and broad band width. the experimental results show that the currenttransformer has a good linearity in the small range of work area, it is immune tohysteresis characteristics in the linear work area and suitable for high-precisionmeasurement of the small range current by the reconstruction of output signalwaveform of the current transformer system.