Fracture Toughness As An Alternative Approach To Quantify The Ageing of Insulation Paper In Oil

Abstract

Oil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. The fast-developing electric power industry demands superior performance of electrical insulation materials which has led to the development of new materials whose measurement of the degree of polymerization has found some practical difficulties. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires the use of alternative methods to the degree of polymerization to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130ºC during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load-displacement curves obtained for different ageing times at the ageing temperature of 130°C was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined.

Prevention of Post Traumatic Radioulnar Heterotopic Ossification Recurrence Using Acellular Human Dermal Matrix: A Case Report and Review of Literature

“…ADM is known to neovascularize in the human body. [7] This property makes ADM more resistant to infection, so ADM is recommended for repair of contaminated abdominal hernias. Some ADMs have been approved by the FDA for use in certain surgical procedures, such as hernia surgery, to reinforce tissue at weak sites.…”