A Dual‐Frequency Sensitivity Model for Optical Fibre Ultrasonic Sensors in Power Transformer Partial Discharge Detection

ABSTRACT The detection of partial discharges (PD) on the power transformer tank demands higher sensitivity in ultrasonic detection. To target the detection frequency band for sensor optimisation and enhance sensitivity, this paper presents a dual‐frequency sensitivity model for optical fibre ultrasonic sensors. Based on coupling resonance principles, the model accounts for the interaction between longitudinal and radial vibrations, yielding two resonant frequencies instead of the single one in conventional models. Through theoretical calculations, the impact of the mandrel’s material and dimensions on the sensor’s sensitivity is analysed, and the sensor structure is optimised accordingly. Experimental validation via a Michelson interferometer reveals that when the aluminium mandrel’s radius and height are 20 mm each, the sensor’s bandwidth can reach 80–200 kHz, aligning well with the typical PD ultrasonic frequency band in power transformers. The experimental results are consistent with the simulation analysis, confirming the validity and accuracy of the proposed model. This advancement not only improves detection sensitivity but also provides a theoretical foundation for designing PD ultrasonic fibre sensors tailored to power apparatus.