Abstract
The thermal aging property of oil-paper insulation is a key factor affecting the service life of transformers. In this study, nano-Al2O3 was added to insulating paper to improve its anti-thermal aging property and delay the aging rate of the insulating oil. The composite paper containing 2% nano-Al2O3 had the highest tensile strength and therefore was selected for the thermal aging test. The composite and normal papers were treated with an accelerated thermal aging experiment at the temperature of 130 °C for 56 days. The variations of the degree of polymerization (DP) and tensile strength of the insulating papers with aging time were obtained. The characteristics of the insulating oil, including color, acid content, breakdown voltage, and dielectric loss were analyzed. The results revealed that compared with a plain paper, the composite paper maintained a higher DP, and its tensile strength decreased more slowly during the aging process. The oil-impregnated composite paper presented a lighter-colored oil, less viscosity changes, and a considerably lower quantity of thermal aging products. In addition, nano-Al2O3 can effectively adsorb copper compounds and keep part of the acid products and water away from the thermal aging process. This characteristic restrained the catalysis of copper compounds and H+ in the thermal aging reaction and reduced the thermal aging speed of both the insulating paper and the insulating oil.
Highlights
The power transformer is the core of power transmission and is one of the key units of equipment for power systems [1]
The insulation performance of the insulating oil can be recovered by changing the oil, whereas the insulating paper cannot be replaced during the operation
Accelerated thermal aging tests revealed that the doping of nano-Al2 O3 can effectively delay the degradation of the degree of polymerization (DP) and mechanical properties of the insulating paper in the aging process and delay the thermal aging rate of the insulating oil [22]
Summary
The power transformer is the core of power transmission and is one of the key units of equipment for power systems [1]. To extend the service life of power transformers, scholars have studied the performance of cellulose-insulated paper for a long time. The addition of ZnO and TiO2 to LDPE and epoxy resin, respectively, effectively improved the volume resistivity, breakdown, and dielectric properties of composites [15,16,17]. Our previous study on nano-Al2 O3 doping on the insulating paper focused on the mechanical, dielectric, and breakdown properties [19]. Accelerated thermal aging tests revealed that the doping of nano-Al2 O3 can effectively delay the degradation of the degree of polymerization (DP) and mechanical properties of the insulating paper in the aging process and delay the thermal aging rate of the insulating oil [22]. The mechanism of the influence of nanoparticle doping on retarding the aging rate of oil-paper insulation was put forward, and verified by the test result of content of copper in oil during the aging
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