Research On F-P Cavity Current Sensing Technology Based On Magnetostrictive Effect

With the development of electric power industry and demand for intelligent and integrated monitoring equipments, conventional current transformers (CT) show their inherent defects, such as giant, potential for catastrophic explosion, and isolated from measured objects, etc. In contrast, to give full pay to OCS's (orthodox current sensor) superiority and role for safe and accurate monitor is an inevitable trend. This paper presents a theoretical model and optimization of a novel optical fiber current sensor based on Fabry-Perot (F-P) cavity multi-light interference theory and magnetostrictive effect of Tb-Dy-Fe material. This optical fiber current sensor is especially suitable for the application of hazardous high-voltage environments due to its characteristics including high sensitivity, immunity to electro-magnetic interference, non-contacted measurement, small size and capability of remote measurement and control. In practical application, it can be hung on a high-voltage wire and measurement range and sensitivity can be adjusted through adjust the distance between the sensor and the high-voltage wire with the advantages of safety and flexibility.Two reflected mirrors of F-P cavity formed by two polished faces of single mode fibers are actuated by an accurate collimating capillary of Tb-Dy-Fe material. The mechanism of this sensor is as follows: the magnetic field produced by the high-voltage wire lead the Tb-Dy-Fe capillary to change length, then the length of F-P cavity will be altered, and the measured current can be detected by the output light reflected from F-P's cavity. The relation is approximately linear between the intensity of output light reflected from F-P's cavity and the measured current when the length of cavity varies in the range ofλ₀ /4(λ₀ is the wavelength of incident light).In this paper, static 2D electromagnetic analysis is simulated by means of ANSYS software, the distribution of the magnetic field in the sensor can be chained, which offers an effective reference for furthercalculation. In order to achieve a well-distributed magnetic field on capillary of Tb-Dy-Fe material, the distance between the sensor and the high-voltage wire was optimized by ANSYS software. The result of theoretical simulation obtained is as follows: the sensitivity is 8nW/A, the distance between the high-voltage wire and transducer head is 30mm, and the range of the measured current is 0A to2000A.Because there is no experimental available condition of high-voltage, the magnetic fields of a solenoid wired with thin wire were used to simulate the magnetic fields produced by the high-voltage wire, and static electromagnetic analysis is presented by means of ANSYS software so as to conclude the output light intensity. It is that the experimental data is agreement with the theoretic analysis. The conclusion is following as: the sensitivity of the experiment device is 17.1952μW/A, the resolution is 0.001mA, while the range of the measured current is 0A to 0. 8A.