Dissolved hydrogen detection in power transformer based on etched fiber Bragg grating

Due to aging and degrading of insulation oil in power transformers, dissolved hydrogen, as a typical fault gas, would produce accompanied by discharges or overheating. Palladium (Pd) film deposited on the surface of chemically etched fiber Bragg grating (FBG) as sensing element by magnetron sputtering process is proposed in this paper. Volume expands when Pd film with 560nm thickness absorbs hydrogen molecules and wavelength shift caused by the strain could be measured. In this principle, hydrogen of low concentration can be obtained through wavelength shift of FBG. Different aspects have been taken into consideration including membrane thickness, polyimide coating and cladding diameter to obtain satisfactory sensitivity. Experimental results in the lab showed that this developed hydrogen could detect 30 μL/L at 1 pm approximately, which proved to be a prospective sensor as a on-line method to be utilized in power transformers.