Comparative analysis of optical-fibre interferometric sensors versus accelerometers: application to vibrations inside high-power transformers

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Abstract
We report the results of calibration of an optical-fibre (OF) probe designed for interferometric measuremen to f vibrations inside high-power transformers. The sensor is highly sensitive in this harsh environment of electromagnetic fields, wide temperature range and oil immersion. A comparative analysis with commercial piezoelectric accelerometers is also presented, focusing on two experiments: the common calibration with a free-space Michelson interferometer that has a controlled moving arm and calibration by obtaining the transference function of magnetostriction in the magnetic laminates by dynamic means. Both methods confirm the extremely high performance of the OF interferometric sensor and the limitations of accelerometers with characteristic low-amplitude vibrations (submicron) and a large range of measurement, as well as for a typical low frequency (100 Hz) but wide bandwidth for the harmonics. The OF probe detects the dynamic strain of deforme de lements and th ed isplacement between them. Proper design of the sensor improves its sensitivity through magnification, reaching a resolution of better than 1 nm. Finally, we demonstrate on-site measurements inside two power transformers.

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