Twenty five years of experience using digitally enhanced processing for on site partial discharge measurements

The introduction of extruded cable systems at 11 kV began in CEGB power stations in the mid 1960s. By the end of the decade, there had been several failures associated with damage and there was a need to be able to audit remaining circuits. These cables were installed in relatively short runs (<1 km) and linked station switchgear with auxiliary equipment. As such, a conventional sample earthed partial discharge circuit could be used-i.e., a coupling capacitor, measuring impedance, detector and a test transformer. However high levels of interference, mainly broadband radio reception, prevented a conventional detector from being used with a sensitivity much better than 100pC. The solution adopted was to apply correlation analysis to extract the data from noise. The added bonus was that the output was a printout particularly suited to contractual testing. Later applications took the technique into areas of phase related analysis and used to provide insight into processes occurring. Whilst the technologies used have long been superseded, this paper is presented as a historical footprint and a description of practical advances which have been made using digital techniques