Acoustical technology applications in large high voltage motors

Acoustical technology has many valuable diagnostic-type of applications. Many of these acoustical techniques are ideal for applyication in large high voltage motors, and in this paper these different methods are described and evaluated. The subject is introduced with an outline of partial discharge (PD) acoustic measurements, with emphasis on how to locate discharge sources in hydrogenerator stator bars. In a completely different application, an ultrasonic technique is described in which sound velocity measurements in stator bars are used for detecting insulation degradation. Another valuable acoustical application is the detection of mechanical changes of a stator bar, such as groundwall delamination. This method is used as a means of early detection of incipient failures of large electric machines. Attention is then drawn to a novel acoustical technology which is used to assess the aging extent of stator insulation in generators. A related subject which is also discussed is the noise signature coming from the motors during the start-up, normal operation and immediately after switch off. Finally, a description is given of an old application of acoustics which is receiving renewed interest, the detection of loose stator wedges