The on-site calibration of fiber optical current transformer is often influenced by the environmental factors, resulting in certain deviation of results. We proposed the sources of uncertainty in this paper, which mainly include: the uncertainty uA(ε) induced by the error of standard FOCT, the uncertainty uB(ε) induced by the field environment and improper operation method, and the uncertainty uC(ε) induced by the calibrator unit. In further, the uB(ε) is analyzed detailed. This component is mainly produced by temperature, vibration and inhomogeneous magnetic field. The experimental results show that the errors of temperature, vibration and inhomogeneous magnetic field are 0.020%, 0.051% and 0.049%, respectively. Finally, we can calculate the synthetic standard uncertainty and expanded uncertainty of the DC calibration (P=99%) are 4.8×10-4 and 1.4×10-3, respectively. And the synthetic standard uncertainty and expanded uncertainty of the AC calibration (P=99%) are 5.6×10-4 and 1.6×10-3 respectively. The results show that the scheme can satisfy the uncertainty requirements of the direct comparison method (0.5S level).
When the λ/4 waveplate of fiber optic current transformer (FOCT) is set in the variable temperature environment, there will be a polarization error during the process of optical signal propagating in the fiber, which will decrease the accuracy of current measurement. In this paper, in order to reduce the influence of temperature change on the accuracy of current measurement, we firstly analyzed the influence mechanism of temperature change on λ/4 waveplate in FOCT, and then used a variable-rate spun fiber (VRSF) as a sensing coil instead of a λ/4 waveplate with circular polarization maintaining fiber (CPMF) as a sensing coil. After that, the mechanism of temperature insensitivity of VSSF was explained. Finally, the two FOCT systems with different fiber sensing coils were tested under variable environment, which proved that the fiber sensing coil using the VSSF in FOCT can effectively resist the interference of the external environment temperature change. As a result, the accuracy of current measurement can be kept within 0.2S degree under the variable temperature environment of -20-70°C.
The principle of fiber optical current transformer and the function of λ/4 wave plate are described in this paper. We propose and demonstrate three kinds of main fabrication errors of λ/4 wave plate, including fiber material error, axial angle error and length interception error. In order to reduce the errors above, an elliptical core polarization-maintaining fiber, which is relatively temperature-insensitive and has a long beat length 20 mm, is used as the wave plate fiber. And we build a set of all-fiber λ/4 wave plate fabrication platform utilizing polarization analyzer and optical microscope. Therefore, the excellent performance λ/4 wave plate (DOP<98%, PER<0.2dB) was obtained with the fabrication platform. Experimental results of DC current measurement (100A˜3000A) and temperature test (-40°C˜85°C) show that the measurement accuracy of prototype with the fabricated λ/4 wave plate is better than 0.2S, which verified that the analysis of fabrication error and optimization technique of λ/4 wave plate in this paper can improves the performance of FOCT effectively
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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