PD detection in inverter-fed machines using acoustic emission sensors.A preliminary investigation

The feasibility of detecting PD in inverter-fed machines using acoustic emission sensor realized using fiber optics was investigated. The sensors, have a frequency response up to 500 kHz and are interrogated using a fiber-optic interferometric system. Three acoustic emission sensors were attached to the stack of the stator to explore the possibility of both PD detection and localization. Results were compared with those achieved using electrical detection and those provided by an ultrasonic camera. Preliminary tests using AC sinusoidal waveforms did show that the acoustic emission sensors and the ultrasonic camera could couple PD activity with the same sensitivity of a conventional electrical PD detection system having a sensitivity of 10 pC. Repetitive voltage impulses were found to cause a high disturbance level in both the acoustic emission sensor and the ultrasonic camera. The noise was ascribed to vibrations induced by the electrodynamic stress due to the impulsive charging current. However, working on the AE sensors in the frequency domain, it was possible to highlight frequency ranges where the PD signal exceeded the disturbance, thus enabling PD detection. The same was not possible for the ultrasonic camera.