The optical fiber interferometric GIS partial discharge ultrasonic sensing system is susceptible to environmental disturbances

which can lead to a decrease in ultrasonic detection sensitivity. The sensing system based on single-loop feedback can suppress the vibration interference

but the working point drift still occurs in long-time operation. In this paper

the reasons for the working point drift of the single-loop feedback sensing system is analyzed firstly and the influence of the hysteresis effect of piezoelectric ceramics is pointed out. Then

a fiber-optic interferometric ultrasonic sensing system based on dual-loop feedback for GIS partial discharge is constructed

and a secondary feedback loop is introduced to compensate for the low-frequency phase modulation error accumulated in the primary feedback loop. After that

through ultrasonic detection tests and GIS partial discharge detection tests under vibration interference

the sensitivity of ultrasonic detection under the dual-loop feedback system is proved. Finally

the real 126 kV GIS partial discharge detection test platform is set up

the partial discharge triggered by metal particles and beating acoustic signals are successfully detected by using the dual-loop feedback sensing system

and the minimum apparent discharge detected is 5.2 pC.