A reflection fiber optic current transformer (FOCT) based on equal-ampere-turn method and range self-expanding approach is proposed to measure ultra-high current in this paper. A flexible sensing coil is utilized in FOCT to suit the needs of the measurement environment and to enable installation and removal. At the same time, two significant difficulties have been raised: one is the nonlinear difficulty introduced by the equal-ampere-turn approach and the range self-expanding method; the other is the non-uniform magnetic field errors generated when the flexible sensing coil is put on site, including conductor eccentricity and non-closed angle, which can amplify the nonlinear problem. Therefore, in order to eliminate the non-uniform magnetic field error, a closed structure of λ/4 waveplate and reflector is designed for the reflection structure, and the sensing coil skeleton is optimized. Experimental results show that the FOCT with closed structure and sensing coil skeleton has a good range self-expanding ability. The accuracy at rated current can also fulfill the requirement of 0.2S. Finally, the FOCT was subjected to a temperature cycle test in the range of -40°C to 70°C, with a ratio error of less than ±0.2%. So the method's validity and feasibility are confirmed.
When the method of dual 90-degree rotation splices in the resonator is used to suppress the zero-bias drift caused by polarization noise of the RFOG, the asymmetry of the two 90-degree rotation splices will cause the Shupe effect error. The mathematical model of the Shupe effect caused by the asymmetry of two 90-degree rotation splices is established and simulated in this paper. The simulation results show that the value of the Shupe effect error is proportional to the asymmetric length of the two 90-degree rotation splices. The Shupe effect error can be suppressed by reducing the asymmetric length.
A fiber optic current sensor utilizing orbital angular momentum (OAM) beam is proposed in this paper. The superposition principle of composite OAM beam is deduced, and the current sensing process is derived by Jones matrix. The current is measured by detecting the rotation angle of petal-like patterns formed after the composite OAM beam through the polarizer. The reflective structure of the sensor doubles the rotation angle, which improves the measuring sensitivity and the reciprocity of the system. Through simulation analysis, we verified that the rotation angle changes linearly with the increase of current, and the sensitivity of the proposed sensor is 0.1254°/A. Finally, on this basis, the angle recognition method is optimized, and the final measurement error is less than ±0.2% in the range of 50A-1500A. .
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