# Characteristic Analysis and Experiment of Adaptive Fiber Optic Current Sensor Technology
## 1 Introduction  
With the development of the smart grid, sensors in electric power systems have stricter requirements. Compared with a traditional electromagnetic current sensor, a fiber optic current sensor has outstanding advantages such as excellent insulation performance, lack of magnetic saturation without ferromagnetic resonance, a wide frequency response range, and good dynamic performance [1, 2]. It has potential application in metering protection, real-time data monitoring, and fault diagnosis analysis in power systems [3, 4].  
The sensing fiber in a fiber optic current sensor is a closed circle structure with good magnetic field characteristics [5], but the fiber is sensitive to temperature changes. When the temperature fluctuates between \(-10\)\({}^{\circ}\)C and \(60\)\({}^{\circ}\)C, the experimental ratio error varies from \(-0.648\%\) to \(0.673\%\). A greater temperature fluctuation exacerbates the fiber optic current sensor error drift [6]. Thus, temperature fluctuations degrade the accuracy of the system, which has become a major limit in its practical application [7]. Many scholars have carried out related research. The influence of ambient temperature on a quarter wave plate and Verdet constant were analyzed in a prior study, and the resulting fiber optic current sensor error expression was derived [8]. Variable temperature parameters and a fiber optic current sensor-equivalent digital control model were introduced, and the influence of temperature on steady-state output accuracy from a fiber optic current sensor was simulated [9].  
Some publications proposed measures for compensating temperature drift based on an analysis of the influence of temperature on fiber optic current sensor accuracy. Compensation of Verdet constant temperature dependence by crystal core temperature measures the temperature of the same volume of crystal that affects the beam polarization in a magnetic field or current sensing process [10]. A suitableinitial phase delay angle can be selected to compensate changes in the Verdet constant caused by temperature when constructing a quarter-wave plate [11]. A polynomial model for describing errors due to temperature fluctuations was also established [12]. Least squares regression was used to determine the polynomial coefficients from experimental data gathered at different temperatures, and errors were dynamically compensated based on the actual temperature. A temperature sensor was also used to measure external temperature changes, and a corresponding algorithm was used to compensate the actual error caused by temperature fluctuations [13]. However, compensation requires accurate temperature measurements of the fiber optic current sensor itself rather than the external ambient temperature, making real-time measurement difficult. It is also impossible to establish a mathematical model relating accurate temperature compensation and output error. The model is complex and the coefficient is difficult to determine, thus the method of applying compensation based on changes in ambient temperature is not feasible.  
The state of art of fiber optic current sensor typically employs Sagnac interference sensors, reflective sensors or polarization-type fiber optic sensor. A detailed review of all-fiber sensors and bulk-optic current sensor [14] stated that the fiber is vulnerable to temperature gradients, and the high Verdet constants in magneto-optic glass allows for sensors with high sensitivities. In order to solve the polarization-type fiber optic current sensor measurement accuracy problem caused by temperature changes, we propose using a magneto-optical glass sensing signal to correct the fiber output signal. An adaptive method of fiber optic current sensor is designed, which provides a new method for solving the temperature drift problem and providing stable operation in a power system.