光纤电流互感器的噪声分析与信噪比优化设计

Noise Analysis and SNR Optimization Design of Fiber Optical Current Transformers

光纤电流互感器(FOCT)易受到各类噪声的影响而导致其测量准确度下降,尤其是在一次电流较小时,因此提高其信噪比是FOCT的关键技术之一。通过全面分析FOCT的光信号噪声、信号检测噪声及外界环境引入的噪声源,给出了FOCT信噪比的计算方法,仿真了不同噪声对信噪比的影响,并在此基础上研制了样机。结果表明:通过提高探测器接收光功率、增加传感头敏感光纤圈数以及选择合适的闭环反馈相位调制偏置工作点等方法,可有效提高信噪比;以此为基础设计的FOCT样机,在额定电流为600 A时,可满足0.2S级要求,1%额定电流下信噪比高达30.2 d B,比差<0.61%,相差<12.39′。提出的信噪比优化设计方法,具有较大的实用价值,对FOCT的设计具有指导意义。

Fiber optical current transformer （FOCT） is easy to be affected by all kinds of noise, which will reduce the measurement accuracy, especially in the case of small current. Therefore, how to improve the signal-to-noise ratio （SNR） is one of the key technologies of FOCT. Consequently, the noise sources of FOCT were comprehensively analyzed, which included the optical signal noise, signal detection noise, and the introduction of noise sources by the external environment, the calculation of FOCT SNR was also given, and the influence of different noise sources on SNR was simulated by the theory. Thereby, a transformer prototype was designed and tested. The results indicate that the SNR can be effectively improved by improving the receiving optical power of the detector, increasing the number of sensing optical fiber ring and selecting appropriate closed-loop feedback phase modulation bias operating point. The prototype can meet the precision demands of 0.2S at a rated current of 600 A. The SNR of the prototype is 30.2 dB while the operating point of system is 1% of the rated current. Meanwhile, the ratio error is less than 0.61%, and phase error is less than 12.39＇. The optimization scheme for improving SNR is of great practical value, and it is instructive for the design of FOCT.