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Ultrasonic signals will be generated when partial discharge occurs in internal insulation faults in large oil immersed power transformers: because the ultrasonic signal has strong anti-interference ability and has no direct electromagnetic contact with the equipment, it is widely used in transformer fault detection and positioning. In this paper, the finite element method (FEM) is used to simulate the ultrasonic signal in a 35 kV power transformer. The influence of transformer case on ultrasonic signal propagation is considered, and the propagation law of the ultrasonic signal inside the transformer is obtained. Fabry-Pérot (F-P) fibre acoustic sensors with a centre frequency of 28 kHz were fabricated. A partial discharge detection test was carried out in a 35 kV transformer winding model using the F-P sensors. The test results show that the ultrasonic waveform detected by the F-P sensors are in good agreement with the simulation results, and the propagation of the ultrasonic wave inside the transformer is verified. It lays a foundation for detecting and locating PDs in power transformer by F-P acoustic sensors.

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