The Study for Overload Operation Limit of Fully Assembled Transportable Nitrogen gas Cushion Type Distribution power Transformer Aihara Y.1, Tsukao S.1, Yamaguchi M.2, Honjo T.2, Sano T.3, Tsumur A.H.4 1TEPCO Power Grid Inc 2Takaoka Toko Co. Ltd 3Meidensha Corp 4Daihen Corp., Japan Online published on 6 February, 2020. Abstract In recent years, TEPCO Power Grid has mainly focused on replacement of aged transformers instead of new installation because the power system has become matured and the power demand has decreased in the network. In order to achieve efficient and systematic transformer replacement work, it is necessary to shorten the outage period and reduce the replacement work cost. For this reason, distribution power transformer that is transportable under fully assembled condition is developed as it omits the on-site assembly and field tests process as well as permits reuse of the existing foundation. The size and weight restrictions on roads, bridges and transport trailers in Japan are more stringent than those in the other Asian countries. Therefore, the transformers need to be designed to be compact so that it can obtain transportation approval from regulatory authorities as well as fits into the substation. Based on the aforementioned considerations, hermetically sealed with nitrogen gas cushion type transformer which is lighter in weight and smaller in overall dimension is adopted. Hermetically sealed with nitrogen gas cushion type transformers are commonly applied in general industries in Japan such as factories which do not require overload performance. However, for distribution power transformer in TEPCO Power Grid, it is necessary to be designed for overload operation in the event of neighbour transformer failure. In order to determine the performance of hermetically sealed with nitrogen gas cushion type transformers under overload condition, model tests were conducted to check the characteristics of nitrogen gas pressure, moisture content in the insulation paper for windings and air bubble generation temperature. As a result of the study, the air bubble generation temperature can be improved by increasing nitrogen gas pressure. Therefore, it is possible to produce hermetically sealed with nitrogen gas cushion type transformers with overload capability by designing the nitrogen gas pressure according to the overload specification. Based on the above study, it is possible to produce hermetically sealed with nitrogen gas cushion type transformer which meets the overload requirement of TEPCO Power Grid. In this way, the intention to transport the transformer under fully assembled condition can be achieved. Top Keywords Oil-immersed transformer, Overload operation, Air bubble generation temperature of the insulation paper for windings, Hermetically sealed with nitrogen gas cushion, Moisture content in the insulation paper, Fully assembled transportable. Top |