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Significance of defects inside in-service aged winding insulations / Sumereder, C. in IEEE transactions on energy conversion, Vol. 23 N°1 (Mars 2008) 

Public ISBD [article]  in IEEE transactions on energy conversion > Vol. 23 N°1 (Mars 2008) . - pp. 9 - 14 Titre : Significance of defects inside in-service aged winding insulations Type de document : texte imprimé Auteurs : Sumereder, C., Auteur ; Weiers, T., Auteur Année de publication : 2008 Article en page(s) : pp. 9 - 14 Note générale : Energy conversion Langues : Anglais (eng) Mots-clés : Weibull  distribution;  electric  breakdown;  insulation  testing;  machine  insulation;  machine  windings;  mica Résumé : This study aims to gain insight into the consequences of local defects in stator winding insulation; therefore, optical (microscopic) inspections and voltage-endurance tests have been carried out on in-service aged generator bars. In this context, generator bars with mica-bitumen insulations and generator bars with mica-epoxy insulations were investigated. The mica-bitumen insulations had been in service for 43 years in a 12 kV hydro-generator. The generator bars with mica-epoxy insulation had been dismantled from two identically constructed 10.5-kV generators after 35 and 36 years of service. The time to breakdown values obtained from the voltage-endurance tests were evaluated using a Weibull distribution. Apart from the scale parameter, Weibull exponent of this distribution allowed for the identification of early failures. The voltage-endurance tests carried out on replacement bars for these generators did not yield any early failures; such failures, however, were detected on both types of the in-service aged insulations. In particular, these occurred at high levels of electric stress and at delaminations between the copper conductor and the groundwall insulation. It is concluded that the interpretation of the measured time to breakdown values and their scatter depends on the level of electric stress. En ligne : http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=4428276&sortType%3Das [...] [article] Significance of defects inside in-service aged winding insulations [texte imprimé] / Sumereder, C., Auteur ; Weiers, T., Auteur . - 2008 . - pp. 9 - 14. Energy conversion Langues : Anglais (eng) in IEEE transactions on energy conversion > Vol. 23 N°1 (Mars 2008) . - pp. 9 - 14 Mots-clés : Weibull  distribution;  electric  breakdown;  insulation  testing;  machine  insulation;  machine  windings;  mica Résumé : This study aims to gain insight into the consequences of local defects in stator winding insulation; therefore, optical (microscopic) inspections and voltage-endurance tests have been carried out on in-service aged generator bars. In this context, generator bars with mica-bitumen insulations and generator bars with mica-epoxy insulations were investigated. The mica-bitumen insulations had been in service for 43 years in a 12 kV hydro-generator. The generator bars with mica-epoxy insulation had been dismantled from two identically constructed 10.5-kV generators after 35 and 36 years of service. The time to breakdown values obtained from the voltage-endurance tests were evaluated using a Weibull distribution. Apart from the scale parameter, Weibull exponent of this distribution allowed for the identification of early failures. The voltage-endurance tests carried out on replacement bars for these generators did not yield any early failures; such failures, however, were detected on both types of the in-service aged insulations. In particular, these occurred at high levels of electric stress and at delaminations between the copper conductor and the groundwall insulation. It is concluded that the interpretation of the measured time to breakdown values and their scatter depends on the level of electric stress. En ligne : http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=4428276&sortType%3Das [...]