Ultrasonic Sensing of Partial Discharges within Microfarad Value AC Capacitors

As new dielectric fluids and materials are introduced, partial discharge (P.D.) testing of microfarad value capacitors in the factory is assuming greater importance. However, the large capacitance restricLs the use of the common electrical methods for detecting small (1-20 pC) discharges, and bridge techniques are not economical for production line tests. For these reasons, the use of ultrasonic sensors for detecting P.D. within microfarad value capacitors was studied, and this resulted in the development of a combined acoustic waveguide probe, ultrasonic sensor and indicating meter, suitable for factory P.D. testing of capacitors.