正弦波调制的全光纤电流互感器故障机理分析

Analysis on Fault Mechanism of Fiber-optical Current Transformers with Sine Wave Modulation

正弦波调制的全光纤电流互感器(FOCT)在直流输电工程中得到了广泛应用,但其在实际运行中故障率远高于电磁式电流互感器,严重威胁电网的安全运行。为研究FOCT的故障机理,建立了FOCT输出信号模型,分析了其调制、解调的基本方法,给出了计算被测电流时所用信号处理方法的影响因素,指出FOCT的光回路及调制回路通过改变探测器输出信号中二次谐波分量的大小而影响FOCT的工作状态,当两回路参数的改变造成二次谐波幅度低于FOCT检测要求时将导致其出现测量故障,并据此将FOCT的故障划分为光回路故障和调制回路故障。仿真计算了光回路和调制回路对二次谐波影响的基本规律,并给出了2种故障的特征差别。最后,开展了FOCT的光回路和调制回路故障模拟试验,试验结果验证了理论分析的正确性。

The current transformer(FOCT)with sine wave modulated fiber-optical has been widely used in DC transmission project,but its failure rate is much higher than that of electromagnetic current transformer in actual operation,which seriously threatens the safe operation of power grid.In order to study the fault mechanism of FOCT,the output signal model of FOCT is established,and the basic methods of modulation and demodulation are analyzed.The influencing factors of signal processing methods used to calculate the measured current are given.It is pointed out that the optical circuit and modulation circuit of FOCT affect the working state of FOCT by changing the second harmonic component in the output signal of the detector.When the second harmonic amplitude is lower than the detection requirements of FOCT caused by changing parameters of two circuits,it will lead to measurement fault.According to this,FOCT faults can be divided into optical circuit fault and modulation circuit fault.The influence of the optical circuit and the modulation circuit on the second harmonic is simulated,and the characteristic difference between the two kinds of faults is given.Finally,the simulation tests of optical circuit and modulation circuit faults for FOCT are carried out.The test results verify the correctness of the theoretical analysis.