Implantable ultrasonic sensor for partial discharge monitoring in large generator stator windings

Corona discharge at the end of stator windings in large hydro-generators can lead to severe insulation degradation, threatening operational reliability. Accurate detection of such discharge is thus critical. Ultrasonic detection, known for its strong immunity to electromagnetic interference, is a promising technique. However, conventional sensors mounted on the generator casing suffer from significant signal attenuation and reflection due to spatial limitations, resulting in reduced sensitivity and accuracy. In this work, a structural component—namely the stator notch block—is modified to function as an implantable ultrasonic sensor without compromising its mechanical support role. The sensor utilizes PZT-5A piezoelectric ceramic and exhibits a peak sensitivity of 64 dB in the 30-650 kHz range. Experimental tests on a full-scale stator bar prototype confirm that the sensor can reliably detect corona discharge signals, with dominant frequency components below 150 kHz. These results establish a viable approach for improving the sensitivity and accuracy of partial discharge monitoring in large hydro-generators.