The leakage current is a main characteristic quantity of contamination level of transmission lines insulator surfaces, measuring insulator leakage current is currently the principal means to monitor the contamination level, but because the environment of transmission lines is very complex, electromagnetic interference will must produce much noise at the time of collecting and testing leakage current, sometime we also get the full wave or half cycle, that means some ways to realize selective measurements, to improve the current sensor's abilities of anti-jamming, selectivity and accuracy when the sensors measure insulator leakage current, an optical fiber sensor was employed to measure leakage current of the insulator strings, which used LED as the photoelectric conversion and light signal stability to detect the current. Some tests in lab were operated that results approved that the optical fiber sensor could achieve selective measurement of leakage current waves, the positive half cycle or negative half cycle, and of cause the full cycle current could be monitored after the differential circuit was improved. It had a great degree of linearity fitting, its sensitivity reached 40mV/mA, and their pertinence coefficients of linear fitting are all more than 99.94%. Its frequency response was 1Hz∼10 kHz, which can meet the basic requirements of the leakage current measurement.
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