Real-time monitoring of transformer status is crucial to the safe and stable operation of power systems. Detection of partial discharge signal in transformers to find potential insulation defects can improve greatly the safety and reliability of high-voltage transformers in power systems. In view of the stability of optical fiber sensing of partial discharge ultrasonic signal in this paper

the study on anti-interference and modulation technology of the optical ultrasonic signal is developed. The influence mechanism of environmental noise on the stability of the sensing system is analyzed. For improving stability of the system

an acoustic-optic modulator is introduced to transfer the phase information to be measured to a high-frequency carrier

and a phase hardware demodulation scheme based on an RF gain-phase detector is adopted. A fiber optic interference ultrasonic sensing system is set up

which eliminates the influence of phase fading problem existing in traditional interference topology on the measurement result. Finally

an experimental platform is set up in this paper to realize the external sensing of partial discharge acoustic emission based on optical fiber sensing. The signal-to-noise ratio of the improved optical fiber ultrasonic sensor is 14.5 dB higher than that of traditional PZT. At the same time of noise and interference resistance

the lower limit of partial discharge detection is 21.83% lower than that of PZT

and the detection sensitivity of partial discharge is 5.3 times higher than that of PZT. It has lower detection lower limit and higher ultrasonic signal detection sensitivity.