Optical fiber sensing technology has significant advantages in partial discharge (PD) ultrasonic detection

but it is susceptible to the variations in parameters such as light intensity

which can lead to output instability and low signal-to-noise ratio (SNR). To address these issues

this paper constructs the heterodyne interferometric optical fiber sensing system that is independent from light intensity and polarization. The system's phase noise and its correlation with the laser linewidth and optical path difference are analyzed through simulations and experiments. The standard sensitivity testing platform and PD experimental platform are established

and the advantages of the heterodyne interferometric optical fiber sensor in terms of sensitivity and ultrasonic detection are compared and validated. By optimizing the system parameter combination

the average SNR in the ultrasonic frequency band is improved by 24.72 dB. Comparative tests show that the developed optical fiber sensing system exhibits a peak sensitivity improvement of more than 15 dB and an average sensitivity improvement of more than 13 dB over piezoelectric transducers (PZT) within the 20~120 kHz detection frequency band. For PD detection in insulation-defect models

the developed optical fiber sensor shows a peak SNR improvement of 12.37 dB compared to the R15α sensor. This study identifies the key constraints on the performance of heterodyne interferometric PD optical fiber sensing systems and proposes parameter optimization methods and a new high-sensitivity PD optical fiber ultrasonic sensor.