NDLI: Investigation and diagnosis of a 184-MVA air-cooled generator heavily affected by slot partial discharge activity

Content Provider	IEEE Xplore Digital Library
Author	Belec, M. Li, S. Nguyen, D.N. Lepine, L. Guddemi, C. Lessard-Deziel, D. Schwartz, T. Lamarre, L.
Copyright Year	2007
Description	Author affiliation: IREQ, Inst. de Rech. d'Hydro-Quebec, Varennes, QC (Belec, M.)
Abstract	For many years, partial discharge (PD) activity has been used in air-cooled generators as one of the important indicators of degradation mechanisms in stator winding insulation. Up to a certain level, these degradation processes are slow. Under normal operation, PD measurement and trending can generally indicate that not only electrical but also mechanical, thermal or ambient (contamination) degradation processes are occurring. Partial discharge activity in air-cooled generators also produces ozone so that the presence of ozone inside and around the generator enclosure is indicative of PD activity. In some cases, the ozone concentration produced by sustained PD activity can reach such levels that it becomes a health hazard for plant personnel. Hazardous levels were recorded in 1991, after 12 years of operation, inside the enclosure of the four 184-MVA hydro generators at BC hydro's peace canyon (PCN) generating station, revealing a situation that was probably active for some years. Results from annual PD measurement performed using PDA (partial discharge analysis) techniques showed an asymmetry in favor of positive discharges that can be the result of slot discharges. Phase resolved partial discharge (PRPD) measurements combined with ozone measurements taken all around the rear perimeter of the generator core were used to confirm the nature of the PDs. Since one of the generators was scheduled for a complete stator winding and core replacement in 2006, an exhaustive investigation was performed before and after replacing the stator. Some stator bars were removed from the slots for visual inspection and extensive laboratory testing. This paper presents results of the on-line PD and ozone measurements, together with findings from visual inspection and laboratory investigations of the retrieved bars. These results were analyzed collectively in order to establish the root cause of the insulation problem as well as the deterioration mechanism of the generator stator winding. Finally, a new pre-installation testing procedure is recommended to prevent such a costly insulation problem from occurring again.
Starting Page	85
Ending Page	90
File Size	1981248
Page Count	6
File Format	PDF
ISBN	9781424404469
DOI	10.1109/EEIC.2007.4562594
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2007-10-22
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Partial discharges Pollution measurement Partial discharge measurement Thermal degradation Insulation Stator cores Stator windings Phase measurement Inspection Laboratories
Content Type	Text
Resource Type	Article

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