Insulation failures resulting from partial discharges (PD) in generator stator windings represent a leading cause of generator breakdowns. Conventional acoustic emission sensors for detecting PD ultrasonic signals are typically made from bulky piezoelectric materials and are restricted to external placement on the generator. Their distant placement from the PD source limits sensitivity. This study presents an implantable piezoelectric thin-film ultrasonic sensor designed for high-sensitivity

real-time monitoring of PD-induced ultrasonic signals within generator stator windings. The sensor features a Pb(Zr0.52

Ti0.48)O3 thin film with an enlarged electrode area to improve sensitivity. In tests using a pencil-lead break on a polyethylene plate as the ultrasonic source

the implantable sensor exhibited a higher peak-to-peak signal than a commercial broadband sensor and nearly twice that of a commercial polyvinylidene fluoride (PVDF) sensor. The implantable sensor demonstrated an upper frequency detection limit of 80 kHz for pencil-break signals

compared to 30 kHz for both the broadband and PVDF sensors. Full-scale generator experiments validated the sensor’s high-fidelity detection of PD signals

emphasising its potential to enhance insulation condition monitoring in power systems.