基于马赫-曾德干涉仪的光纤电流互感器设计

电流互感器作为一次侧电流的常用计量设备之一，它在电力系统的交流电测量、继电保护、电力设备检修控制等相关领域均具有十分重要的地位。针对传统电流互感器存在的线性度低、抗干扰能力差及精度低等问题，尤其在工频小电流精确测量这一难题方面更是捉襟见肘。鉴于此，本文提出一种基于马赫-曾德干涉仪的光纤电流互感器。该互感器利用电流经过电阻所产生的焦耳热改变光纤中的光信号特征，从而引起马赫-曾德干涉仪的输出信号变化，然后通过光电探测器完成对干涉仪的光信号捕捉，并将其转换为电信号输出，完成工频小电流检测。结构上通过采用PCB型罗氏线圈作为感应取电装置，并利用MATLAB完成其动态响应分析。另外针对信号采集、传输、处理过程中所出现的噪声信号，设计了基于FPGA技术的信号处理系统，以提高信噪比。最后通过实验对工频小电流进行测量，线性度为0.996 1,检测精度可达到0.14%。实验结果表明提出的光纤电流互感器相较于传统光学电流互感器相比，具有更高的线性度和测量精度，为基于热效应的电流互感器发展提供了新的思路，也为工频小电流的测量提供了一种新的方法。

Design on fiber optical current transformer based on Mach-Zehnder interferometer

As one of the common measurement equipment of primary side current, the current transformer plays an important role in AC current measurement, relay protection, power equipment maintenance control and other related fields of the power system. To address the problems of low linearity, poor anti-interference ability and low precision existing in traditional current transformers, it is especially difficult to accurately measure the low power frequency current. In view of this, a fiber optic current transformer based on the MachZehnder interferometer is proposed in this article. The transformer uses the Joule heat generated by the current passing through the resistance to change the optical signal characteristics in the fiber to cause the change of the output signal of the Mach-Zehnder interferometer. Then, the optical signal of the interferometer is captured by the photodetector and converted into electrical signal output to complete the power frequency small current detection. In the structure, the PCB-type Rogowski coil is adopted as the induction device, and its dynamic response analysis is completed by MATLAB. In addition, a signal processing system based on FPGA technology is designed to improve the signal to noise ratio. Finally, the small power frequency current is measured through the experiment. The linear correlation coefficient is 0. 996 1, and the detection accuracy can reach 0. 14% . The experimental results show that the proposed fiber optic current transformer has higher linearity and measurement accuracy than the traditional optical current transformer, which provides a new idea for the development of current transformers based on thermal effect. It also provides a new method for the measurement of power frequency small current.