Investigations Of Optical Fiber Current Transducer Based On BGO Crystal

Optical fiber current transducers (OCTs) are new-style sensors based on the optical fiber sensing techniques, photoelectric techniques, nonlinear optics and signal processing techniques. Because of their natural characteristics and inherent advantages, OCTs have been widely used in electric power systems and have more economic benefits.Investigations on the sensing materials are very important issues for OCTs. Recently, BGO crystal as an excellent electro-optic material has been widely used in optical voltage sensor. However, there are few studies on utilizing BGO crystals for OCTs. The feasibility of using BGO crystals for OCTs has been demonstrated both theoretically and experimentally in this paper, which found the basis of the technique for measuring the current and voltage simultaneously.This paper mainly investigates a hybrid OCT, which utilizes a BGO crystal acting as sensing element. First of all, based on the theoretical analyses of the magneto-optical properties of a BGO crystal, the Verdet constants of a BGO crystal at different wavelengths are measured by employing the double frequency method. And the experimental results agree with the theoretical values. By combining the measured absorption coefficients with the relations between the Verdet constants and light wavelengths, the magneto-optical figure of merit of BGO crystal is presented. Additionally, the magneto-optical properties of BGO crystal are compared with that of some magneto-optical glasses usually used for OCTs. The results show that BGO crystals are suitable for fabricating OCTs.Secondly, by analyzing the output signals of the OCT, we have designed two types signal-processing systems: a pure analog electric circuit and an intelligent opto-electric system. Of which, the pure analog electric circuit has already been used in the experiments. And the results demonstrate that the system is feasible.Additionally, an OCT based on the use of a BGO crystal as a magnetic field sensor together with a ferromagnetic core with an air-gap as a field concentrator is designed and experimentally demonstrated. The results show that the system possesses a good linearity and a large dynamic range. However, there exist certain errors between the measured and the real values.Finally, the origins of the errors and the methods for omitting the errors are analyzed and discussed in detail. The influences of the phase shift caused by the reflection, which are the main resources of the errors, are theoretically analyzed and numerically simulated.The results of theoretical analyses and experiments demonstrate that the hybrid OCT based on BGO crystal can be developed into a practical OCT with good performances.