Abstract
Dissolved hydrogen is a symbol gas decomposed by power transformer oil for electrical faults such as overheat or partial discharges. A novel D-shaped fiber Bragg grating (D-FBG) sensor is herein proposed and was fabricated with magnetron sputtering to measure the dissolved hydrogen concentration in power transformer oil in this paper. Different from the RI (refractive index)-based effect, D-FBG in this case is sensitive to curvature caused by stress from sensing coating, leading to Bragg wavelength shifts accordingly. The relationship between the D-FBG wavelength shift and dissolved hydrogen concentration in oil was measured experimentally in the laboratory. The detected sensitivity could be as high as 1.96 μL/L at every 1-pm wavelength shift. The results proved that a simple, polished FBG-based hydrogen sensor provides a linear measuring characteristic in the range of low hydrogen concentrations in transformer oil. Moreover, the stable hydrogen sensing performance was investigated by X-ray diffraction analysis.
Highlights
Most oil thermal and electrical faults inside the transformers decompose the oil and other organic components to produce dissolved hydrogen; it is important to detect the health status of transformers by monitoring dissolved hydrogen
D-shaped fiber Bragg gratings have a high sensitivity to curvature owing to the non-circular symmetry of its physical structure, which attracts much interest
Since the cross-section shape of the optical fiber is similar to English alphabet D after being grinded, it is called a D-shaped fiber Bragg gratings (FBGs) (DFBG)
Summary
Most oil thermal and electrical faults inside the transformers decompose the oil and other organic components to produce dissolved hydrogen; it is important to detect the health status of transformers by monitoring dissolved hydrogen. Micro-mirror fiber optic sensors have been shown to be feasible in sensing dissolved hydrogen in oil or liquids [2,3], but they are not suitable to monitor dissolved hydrogen in power transformers for field applications. A FBG refractive index sensor for magnetic field or current characterization based on a grating region polished to the fiber core was proposed and demonstrated in [12,13,14]. D-shaped structure which the of cladding is laterally polished to a smallfibers distance core, which can increase thein sensitivity fiber sensors. To polished to a small distance to the core, which can increase the sensitivity of fiber sensors. It is necessary to take a compromised and comprehensive consideration of consideration of the polishing depth to guarantee both mechanical strength and sensitivity. Analysis wasTocarried out. into the membrane performance, X-ray diffraction (XRD) analysis was carried out
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