A fiber optic AE sensor system based on over-coupled fused coupler (OCFC) and intensity modulate principle is investigated to detect power transformer partial discharge effectively. The principle of a sensing heads based on OCFC for detection of acoustic emissions in power transformers is illustrated. The theory and experiment results of fiber optic AE sensor based on OCFC is described, the transmission spectrum of these OCFC sensor when applied with different strains is investigated. A distributed feedback laser was used to interrogate the sensors, optimizing the measurand readout sensitivity. The output of these AE sensors when applied with acoustic emission is shown. The sensitivity, frequency responses and the minimal discharge are experimentally obtained. Experiment show the OCFC AE sensor has the flat response from 40k to 120 kHz, the average sensitivity is about -70dB, and the minimum detection discharge quantity is 50pc.
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