Temperature and load correlated on-line PD measurements on a Danish 6,4MVA Power Generator

Monitoring of the PD level of a 10kV, 6.4MVA generator in a Danish Power Plant over a couple of years has caused increasing concern about the generator´s VPI insulation condition. This paper presents an analysis of the PD activity in the generator with an advanced PD monitoring system. The measurements were performed as on-line measurements during normal operation as well as during the start up and shut down sequences. Winding temperature and the generator load were recorded simultaneously with the PD measurements. A correlation has been established between the temporal development of PD intensity and factors like winding temperature and load level. Analyses were performed on the PD development with respect to pulse magnitude and frequency, including advanced pulse shape analyses, in order to determine PD-origin and characteristics. A comparable high PD level was recorded which, combined with experiences from early types of generators with global VPI insulation, led to the decision that the generator should be refurbished. The results described and analyzed in this paper are based on the service period with the original insulation until refurbishment.