Characteristics And Mechanisms Of Aging Of Oil-paper Insulation In Power Transformers

Power transformer is the key equipment in power system and stands an extremely important position. It is of great significance to guarantee transformer operation reliably. The life of transformer is limited to the life of its oil-paper insulation. It degrades as the time goes by, and eventulally its capacity of exposure to short-circuit current has been significantly lowered and becomes a hidden threaten to system security. Therefore, studying the aging characteristics and mechanisms of oil-paper insulation, through accelerated aging experiments and onsite experiences, can provide information and references for transformer insulation condition-based assessment and also lifetime forecasting.On the basis of summarizing the domestic and international oil-paper insulation aging research results, the mechanisms that how the main factors affecting oil-paper insulation aging function and how the main chemical characteristic parameters change are analyzed. Through thermal accelerated aging experiments, the correlations of main chemical characteristic parameters and the relation of such parameters with aging time are studied, the aging mechanisms and dynamics are discussed, the generation rate of those characteristic products are also analyzed. The main conclusions are:1. Compared to ordinary Kraft paper, Munksjo paper has good thermal stability and lower furfural output. The types of oil and paper are needs to be considered when using furfural for oil-paper insulation aging estimating. The attention value of furfural in oil should be formulated based on its corresponding oilpaper insulation types.2. Compared to 25# transformer oil, BIOTEMP oil has higher saturated moisture content. This leads to its rapid aging and correspond to higher value of acid number, it may cause serious corrosion to transformer internal metal components. BIOTEMP oil can effectively inhibit oil-paper insulation aging when using with ordinary Kraft paper but without tangible results when using with Munksjo paper.3. In the process of oil-paper aging, cellulose bond scission rate is not strictly random, the degradation rate decreased exponentially with aging time. The remaining life will be shorten when using the random-scission model for lifetime prediction, due to it ignores the decline trend of degradation rate in the latter part of aging.4. Generation rates of characteristic products are consistent with the change of bond scission rate of cellulose, when samples were in mid-end life and aged further, the generation rate decreases almost exponentially.