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This paper presents an evaluation of the performance of different methods for estimating the parameters required for the application of the Disruptive Effect Model to the analysis of the breakdown characteristics of 15 kV distribution insulators subjected to lightning impulses. The tests involved the application of both the standard (1.2/50 μs) and non-standard lightning impulse voltage waveshapes (1.2/4 1.2/10 3/10 μs) and 7.5/30 μs)of positive and negative polarities. The obtained Vxt characteristics are compared with those predicted by the Disruptive Effect Model using the most common procedures for estimating the parameters necessary for its application, including a novel method which is presented in the paper. An analysis of the results relevant to the various procedures shows that the parameters obtained according to the proposed method lead to a better agreement between theoretical and experimental results. [ABSTRACT FROM AUTHOR]

Abstract: Cable lines impart attenuation and distortion to overvoltages coming from overhead lines. In particular the attenuation is an important factor for the insulation coordination of a cable line and consequently for its reliability. The evaluation of such attenuation needs the utilization of numerical programs and their utilization, although it becomes an obliged step, is not an easy task without a specific skill. In this paper a simplified method is proposed which is based on the results of a specific numerical program, in order to evaluate the overvoltage attenuation introduced from cable lines for both the conductor screen (insulation stress) and screen to ground (jacket stress) modes of propagation. Although such method introduces some approximation, it is a useful tool in order to have both a first and conservative evaluation of the overvoltage stressing the cable line insulation when the impinging overvoltage to the cable line is known. [Copyright &y& Elsevier]

The partial discharge (PD) pulse burst characteristics of a transformer type synthetic organic ester fluid were compared with those of an equivalent transformer type mineral oil. Wide and narrow bandwidth measurements were carried out to determine simultaneously the apparent charge transfers associated with the overall PD pulse burst as well as that of the individual discrete pulses within the PD pulse burst. The PD pulse burst behavior was found to be similar in both insulating liquids. The discharge cavity formation times ranged from 0.5 to 1.5 μs, while the charge transfers associated with the PD pulse bursts in the liquids were found to extend from approximately 5 to 30 pC. [ABSTRACT FROM AUTHOR]

Presents a study that examined the aging process of mineral oil-impregnated-high density kraft paper capacitor bushing models subjected to voltage switching surges. Effects of the removal of electrical impulse stress over a finite time period; Thickness of the insulating system of the model capacitor bushing; Implication of the partial discharged inception stress characteristics for the doubled insulation specimen.

An innovative theory—derived from the “enlargement law”—about how to compare the breakdown performances of power cable insulation compounds is illustrated and applied herein. This theory enables the selection between two different compounds candidate for the insulation of power cables via dielectric strength tests performed on cable models. In particular, compound performances are investigated vs. cable length looking for the so-called crossing length, i.e. a crossover point between the performances of the two compounds, such that one of the two performs better above this length, and conversely the other below it. The application of this theory consists in a comparison between two EPR compounds, based on lightning impulse breakdown tests realized on mini-cables, and shows that the crossing length depends strongly on cable size and voltage rating. Therefore, the practical selection of the best compound must consider the typical installation lengths of real cables. Finally, the relationship between crossing quantities and failure probability is analyzed, highlighting that while crossing length does depend on failure probability, crossing strength and breakdown voltage do not. Thus, since crossing strength depends mainly on compounds Weibull parameters, it is the key for comparing the intrinsic breakdown characteristics of competing compounds. [Copyright &y& Elsevier]

This paper presents the results of the application of a novel method to estimate the parameters of the Disruptive Effect Model for the prediction of the volt–time curves of 15 kV insulators. Besides the standard lightning impulse voltage waveshape, four non-standard impulse waveshapes (namely 1.2/4 μs, 1.2/10 μs, 3/10 μs, and 7.5/30 μs), of both polarities, were adopted in the tests. The measured volt–time characteristics of a 15 kV class pin-type insulator were compared with those predicted by three different procedures related to the Disruptive Effect Model: Darveniza and Vlastos, Hileman, and the one recently proposed by the authors. The results show that for some impulse waveshapes and polarities, the methods by Darveniza and Vlastos and by Hileman do not predict insulator breakdown for the lower voltage levels. On the other hand, a relative good agreement is found between theoretical and experimental results for the calculations performed using the method proposed by the authors. [ABSTRACT FROM AUTHOR]