- перевод в СНТД / prestressing

There is nothing original in the proposition that mechanical stress has a controlling influence on the propagation of electrical trees in insulating materials.

Over a quarter of a century ago, Billing and Groves and later Arbab and Auckland were discussing the effect of externally applied mechanical stresses-for example by bending-on tree growth.

In a simple bending experiment, it is immediately obvious that tree growth is accelerated in regions of tensile stress and retarded where compressive stress is present.

The effect of internal stresses on electrical tree growth, determined by photo-elastic techniques, was also reported by Champion, et al. and David, et al. in 1992 and 1994, respectively.

Whereas the above were concerned with laboratory specimens, similar conclusions have also been drawn from more practical applications, such as in cables, in numerous publications from Densley in 1979 through to Ildstad and Hagen in 1992.

Общеизвестен факт, что рост дендритов в изоляторе можно контролировать при помощи внешнего механического воздействия давлением.

Более четверти века назад Биллинг и Гровс, а позже и Арбаб и Окланд рассматривали вопрос использования внешнего механического давления на рост дендритов например, при изгибании.

В простом эксперименте с изгибанием сразу становится очевидным увеличение роста дендритов в зонах с загрузкой при растяжении и уменьшение роста дендритов в зонах с нагрузкой сжатия.

Влияние внутреннего давления на рост дендритов, определенное с помощью оптических методов определения напряжения, было описано Чемпионом и др. и Дэвидом и др. в 1992 и 1994 годах соответственно.

В то время как все вышеуказанное проходило в лабораторных условиях, подобные выводы были обнаружены на практике, например, в теории кабелей, в многочисленных публикациях от Денсли в 1979 году до Илдстада и Хагена в 1992 году.

The theoretical analysis of the mechanical aspects of tree growth began with Zeller, et al., who attributed the growth of filamentary cracks to electrostatic forces, a process they named electrofracture. This theoretical approach has been developed subsequently by Hikata, et al. and Fothergill.

On the basis of this approach to an understanding of the physical processes, there is a strong temptation to interpret electrical tree growth in terms of fracture mechanics, but the analogy must not be pushed too far. Certainly, it is possible to draw a direct correlation between treeing characteristics and the mechanical properties of insulating materials. A preliminary study of tree inception and growth in materials of greatly differing mechanical properties revealed that the mechanical characteristics of the material were paramount. It was proposed that the residual mechanical stress developed under alternating voltage application produced fatigue cracking in the inception phase. Since crack formation is determined by, among other things, tensile strength, it followed that this parameter would influence the tree initiation time. This view was supported by measurements of the tree inception times of polyester resin and an elastomer (PL-3). The tree inception time in the elastomer was less than 30% that of the polyester resin, which had a tensile strength five times greater than that of the elastomer.