NDLI: Insulation characteristics of epoxy insulator with internal void-shaped micro-defects

Content Provider	IEEE Xplore Digital Library
Author	Ueta, G. Wada, J. Okabe, S. Miyashita, M. Nishida, C. Kamei, M.
Copyright Year	1994
Abstract	Presently, an increasing number of gas insulated switchgear (GIS) has been operated for longer than 30 years, which is generally considered their service life. The degradation in solid insulators is considered to be one of the key factors determining the service life of such highly aged GIS in terms of insulation. Under normal circumstances, GIS insulators have outstanding electrical performance and insulation failure is considered unlikely within the design life of 30 years or so, provided the units conform and have passed the partial discharge (PD) test. However, assuming operation beyond 30 years, the insulation characteristics must be clarified in case ultra-microscopic defects undetectable via the PD test are present inside insulators. Accordingly, in the preceding study, micro-defect models in three types of shape (void, crack, and delamination) with an apparent PD of 1 pC in an actual 550 kV-GIS spacer, were designed and produced. Of those three, the present study covered void-shaped defects and obtained breakdown voltage-time (V-t) characteristics through an electric field (EF) acceleration test. These V-t characteristics were extrapolated to evaluate the breakdown risk in 30 to 50 years operation, which is considered the design life of GIS. As a result, void-shaped defects of about 1 pC were evaluated as highly unlikely to cause any problem according to the 50% value of the V-t characteristics. Given the relatively large dispersion among the breakdown times in the EF acceleration test results, a study was subsequently conducted with this dispersion taken into account. The probability of breakdown within 50 years was evaluated at less than 0.1%, assuming an operating EF of 4 kVrms/mm. Furthermore, when considering the location parameter that does not result in breakdown within a certain period, the probability of breakdown was considered to be much smaller. In fact, since the declining gradient of the V-t characteristics is considered smaller in the long time region, evaluation by extrapolating the V-t characteristics in the present study is considered sufficiently safe. The Vt characteristics obtained have made it possible to evaluate the period to breakdown and the breakdown risk where ultra-microscopic voids are present.
Sponsorship	National Natural Science Foundation of China (NSFC) Region Centre Ville de Tours Conseil General D'Indre et Loire ABB IEEE Sandia National Laboratories TOSHIBA
Starting Page	535
Ending Page	543
Page Count	9
File Size	578022
File Format	PDF
ISSN	10709878
Volume Number	20
Issue Number	2
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2013-01-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Partial discharges Insulators Gas insulation Acceleration Shape breakdown voltage-time (V-t) characteristics Gas insulated switchgear (GIS) epoxy insulator micro-defect void partial discharge (PD)
Content Type	Text
Resource Type	Article
Subject	Electrical and Electronic Engineering

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