Ultrasonic emissions from nonceramic insulators with defects

This paper documents the results of an investigation into the frequency distribution and magnitude of ultrasonic emissions (UE) from nonceramic insulators (NCI) with defects that result in partial discharge activity. The objective of the investigation was to obtain more complete knowledge of the acoustic energy emitted by defective NCI so that the technique may be optimized for in-service inspection of defective NCI. The range of measurement frequency was 10-160 kHz, but most of the emissions occurred in the 30-50-kHz range and were only slightly affected by defect types. The magnitude of the ultrasonic emissions increased proportionally with increases in partial discharge magnitude, but discharges internal to the rubber weather-shed material were almost impossible to detect because of the attenuation by the surrounding polymeric rubber material