建立了光纤电流互感器的离散动态模型，理论分析了互感器比值误差及相位误差与系统环路增益之间的关系，确定了环路增益漂移是导致互感器长期运行精度劣化的主要原因之一。提出了一种环路增益在线监测方法，能实时检测环路增益的变化，监测值可以作为互感器长期运行的故障监测点之一。在此基础上实验验证了模型的正确性，结果表明：在保证静态测试精度的条件下，系统环路增益取值越大，环路增益波动对互感器比值误差和相位误差的影响越小。系统环路增益取值为0.05时，为保证长期运行互感器测试准确度不超过误差限值要求，环路增益波动应不超过10%。

A discrete dynamic model of fiber optical current transformer is established. The relationship between the scale factor error, phase error of the transformer and the system loop gain is theoretically investigated. It′s determined that the loop gain drift is one of the main reasons that lead to the degradation of the long-time operation accuracy of the transformer. A method for online loop gain monitoring is presented which can monitor the change of loop gain in real time. The monitoring value can be used as one of the fault monitoring points for long-time operation of the transformer. Based on it, the model correctness is verified by experiments. Results show that on the condition of ensuring the static test accuracy, the greater the system loop gain value is, the smaller the influence of loop gain fluctuation on scale factor error and phase error of the transformer will be. When the system loop gain is 0.05, the loop gain fluctuation should not exceed 10% to ensure that the transformer measurement accuracy in long-time operation is less than the required error limit.