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The condition assessment of oil–paper insulation is a vital issue in transformer management. To investigate the effect of moisture content on the accuracy of the prediction model, accelerated ageing experiments were performed with different initial moisture content (IMC) in laboratory condition. Two types of multi-parameter lifetime prediction models, e.g. with and without consideration of IMC, were presented for comparison purpose. The authors found that a better accuracy for its prediction results could be achieved by establishing the prediction models with the consideration of IMC. Besides, models considering IMC have better economic feasibility than that without considering IMC(non-IMC) as its total cost is cheaper according to life cycle cost (LCC) calculations. In addition, failure probability based on the proposed prediction models was also calculated as a direct indicator for evaluating the oil–paper insulation status. [ABSTRACT FROM AUTHOR]

This paper presents an experimental work investigating the failure data of oil-impregnated paper under pulsating DC voltage. The failure data of the oil-impregnated paper specimens were obtained through constant voltage stress tests; the Weibull distribution was used to estimate the statistical distribution of failure data. The exponential function (EF) and the inverse power function (IPF) were used to modify the Weibull distribution of failure data, so as to obtain two dual-variable Weibull failure distributions (WFDs), which were used to analyze failure data of oil-paper specimens obtained under pulsating DC and individual DC and AC voltages. Their adequacies were evaluated by using failure data obtained through the constant stress tests under various voltages. Both EF-modified and IPF-modified WFDs show more adequacy for failure data of oil-paper insulation under DC and pulsating DC voltages than AC voltages. The EF-modified WFD was more adequate than IPF-modified WFD in estimating the statistical distribution of failure data. [ABSTRACT FROM PUBLISHER]

Abstract: Graphene oxide (GO) paper is a promising candidate for novel applications in energy storage systems such as electrical batteries, supercapacitors and multi-layered composites where the material undergoes deformation mechanisms. In particular, the strength of graphene oxide paper is critical in such applications and is defined by the interaction between the GO sheet constituents of the paper. The deformation behavior and tensile strength of focused ion beam (FIB) fabricated GO micro-beams was measured using in situ atomic force microscopy (AFM). GO sample deformation and failure was dependent on both the size of the micro-beams and the environmental testing conditions. Specifically, the failure stress of GO paper micro-beams tensile tested in air was found to increase when compared to testing in vacuum. This environmental dependent tensile strength of GO paper is attributed to water promoting stress transfer between GO sheets within the paper for higher strength during air testing while vacuum conditions remove water, leading to poor stress transfer between GO sheets for lower tensile strength results. A two-parameter Weibull distribution is introduced to quantify the micro-beam size dependent strength, which is attributed to interfacial defects determining GO paper failure strength. [Copyright &y& Elsevier]