Based on the transverse electro-optic effect of lithium niobate crystal, combined with polarizers and Faraday rotator, this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method, and the feasibility of the scheme is verified by both the theoretical and experimental evidences. The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency, improves the sensitivity and stability of the system, and reduces the volume and cost of fiber optic current transformer. The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect, which enhances the signal to noise ratio and simplifies demodulation mode. The experimental results show that the current ratio errors measured at room temperature range from 1% to 120% of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S. The temperature stability of the current transformer is also tested, and the ratio error measured at the rated current does not exceed ±0.2% in the range of -30 °C to 50 °C.

中文翻译：

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新型调相方法的新型光纤电流互感器

基于铌酸锂晶体的横向电光效应，结合偏振器和法拉第转子，提出了一种采用空间不可逆调制方法的共线闭环光纤电流互感器，并验证了该方案的可行性。理论和实验证据。该检测方案避免了感测光纤线圈的过渡时间对调相频率的限制，提高了系统的灵敏度和稳定性，降低了光纤电流互感器的体积和成本。采用锯齿波调制方案，通过锯齿波的相移实现相位偏置调制和反馈调制，达到闭环检测效果，提高了信噪比，简化了解调方式。实验结果表明，室温下在额定电流的1％〜120％范围内测得的电流比误差符合国标GB / T 20840.8-2007的要求，精度达到0.2S。还测试了电流互感器的温度稳定性，在-30°C至50°C的范围内，在额定电流下测得的比率误差不超过±0.2％。