92_repetive_epoxy - 754 IEEE Transactionson Energy...

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754 IEEE Transactions on Energy Conversion, Vol. 7, No. 4, December 1992. INVESTIGATION OF THE EFFECT OF REPETITIVE VOLTAGE SURGES ON EPOXY INSULATION G.C. Stone' R.G. van Heeswijk R. Bartnikas Ontario Hydro University of Waterloo IREQ Toronto, Canada Waterloo, Canada Varennes, PQ, Canada Abstract - ?he aging of epoxy elsctrical insulation by unipoh, rep& voltage swges has been investigated to determine whether such surges can precipitate premature fi high voltage motor windings and gas insulated switchgear spacers. A fuu factorial statistical test was devised performed on 180 pure epoxy insulation specimens to examine the effmt of wltage magnitude, polarity surge repetition mte on we unjtlfed epoxy specimens containing a needle-plane elecSmde pmeby. All factors interactions were determined haue a [email protected]@ant effmt on life, life prediction equations were estimated Increasing wltoge magnitude or repetition mte, decreased or increased ljfe, respectively. Aging was found otxur at as low a stress 2 MV/crn An important conclusion is that gmdd aging epoxy does occur under repem wltage surges. Based on a realistic number of surges with typW wltage amplitudes which can normally occur from uacuum switchgear during service. gmdual deteriomtion the epoxy turn insulation in motor stator windings passible in some situations. Situations where surge aging mag occur are ialentjfwr INTRODUCTION Voltage surges have long been known to cause failure of the solid electrical insulation in high voltage equipment such as motors, generators, cables, transformers and switchgear. However, it has commonly been assumed in the past that as long the insulation does not break down during a surge, there is little or no lasting effect on the insulation. That is, in the absence of direct evidence to the contrary, it has been assumed that there is no measurab!e deterioration or aging of the insulation due to repeat application of voltage surges. Since most equipment is exposed to only a relatively few large surges (eg. such as those caused by lightning or power system switching) over its lifetime, the assumption of no effective aging is probably valid in most situations. Over the past decade, it has become apparent that certain types of electrical equipment might be exposed to many thousands or tens of thousands of relatively large voltage surges over its lifetime. In particular vacuum switchgear, * Canada. Now with Iris Power Engineering, Mississauga, Ontario, 92 WM 067-9 EC the IEEE Electric Machinery Committee of the IEEE Power Engineering Society for presentation at the IEEE/ PES 1992 Winter Meeting, New York, New York, January 26- 30, 1992. Manuscript submitted August 30, 1991; made available for printing December 6, 1991. A paper recommended and approved by which is now becoming a popular means of switching high voltage motors, can readily create several hundred voltage surges per switching-on event, as compared to the single surge usually accompanying the conventional air-magnetic switchgear operation 111.
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92_repetive_epoxy - 754 IEEE Transactionson Energy...

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