From the editors´ desk

This issue has five articles. The first is ???Study of ´Code Absence´ in the IEC Three-Ratio Method of Dissolved Gas Analysis,??? by Zhi-xiong Liu, Bin Song, and En-wen Li of Wuhan University, China; Yuan Mao of the Hong Kong Polytechnic University, Hong Kong; and Guo-li Wang of the National Engineering Laboratory for UHV Engineering Technology, China. This article discusses the fault codes for various fault conditions according to the IEC three-ratio method and, in particular, the fault type with code 011, which has not been defined and is referred to as ???code absence.??? On occasion, in the inspection of transformers, code 011 will be encountered, which can be due to one of four types of faults, namely, partial discharge, low temperature overheating, high temperature overheating, and arc discharge. Regression analysis shows linear relationships can correlate H2, C2H6, and C2H4 to CH4 for the same fault type, but the slopes of the linear relationships are different for different fault types. Among them, partial discharge fault can be expressed most accurately for code absence. The second article is ???Aging Assessment of Dielectric Vegetable Oils,??? by Juan Carcedo, Inmaculada Fern??ndez, Alfredo Ortiz, Fernando Delgado, Carlos J. Renedo, and Carmen Pesquera of the University of Cantabria, Spain. In this article, mineral and two different vegetable oils and Kraft paper aging are analyzed after having been thermally accelerated and aged at 110, 130, and 150°C. Physical, dielectric properties, moisture content, acidity, dissolved gases, loss factor, and DC resistivity for the different types of oil and the moisture content and degree of polymerization for Kraft paper are reported. As such, this is a comprehensive study on the aging of vegetable oils compared with mineral oil under different working conditions.