New methods of partial discharge measurement for the assessment and monitoring of insulation in large machines

New online partial discharge (PD) measuring techniques for the assessment and monitoring of the insulation in large rotating machines are introduced. These nonintrusive and flexible techniques use purpose-built high-voltage high-frequency current transformers (HVHFCT). The PD signal from the CT is sent directly to a digital oscilloscope for measurement and analysis. The HVHFCT is also suitable for live-line PD measurement, in which the CT is temporarily placed outside the machine, greatly simplifying PD measurement. The CT characteristics and their applications are presented and discussed. The authors have also investigated an online or live-line PD calibration method for quantitative PD measurement. Thereby, even the first PD measurements from different machines can be compared. The calibrator can also be used to evaluate the performance of existing online PD monitoring devices. The calibration methods, and their performance, are described and discussed