Study On Spectrum Absorptive Optical Fiber Acetylene Gas Sensor Based On Frequency Harmonic Detection Technique

Operation safety of large-scale transformer in electrical power system isof practical significance. With the rapid development of the electric powerprojects and electrization of industrial corporations, more and moretransformers have been used. When in operation, transformer oil will perhapsproduce some malfunction gases. This thesis was concentrated on highlysensitive on-line remote sensing of fault gases for transformer isolation oil onthe basis of optical fiber.Optical fiber gas sensor has found a wide range of applications by virtueof its various technical merits. In this paper, the development of optical fibergas sensors was thoroughly reviewed, from which some drawbacks andapplication limitations of on-going optical fiber gas-sensing techniques wereextracted. In this article, using the spectrum absorption method, themalfunction gas in the transformer oil is on-line detected remotely with highsensitivity, and the optical signal transmitted by optical fiber. Thetransformer's work state can be watched. Harmonic detection technique ofgas concentration sensing based on infrared absorption phenomena of gaseswas presented. This was a novel optical fiber methane sensor. This methodoffered high selectivity, long life, no influence of surroundings gases, noelectrical induction and so on. It adapted to be used in the foul and hazardousenvironment.In the paper, the center absorption wave, the absorption shape, the gapbetween the adjacent lines and the intensity of absorption line are analyzedusing quantum mechanics knowledge and molecular spectrum theory. It givesthe theoretic description of the Beer-Lambert law.The designs of the light path, circuit and gas cell are based on thetheoretic analysis in the paper. For the signals are very weak, the lock-inamplifier is employed to extract the signals in the circuit design. It can inhabitthe noise in the most and maximize the signal-to-noise.The feasibility of system design of Acetylene gas density harmonicmeasurement is proved by the optical fiber loss experiment and the experimentof gas density and second harmonic relation etc. The results of the experimentsare given in the end of the paper.