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The main function of transformer is to change voltage level. Then electric power can be delivered to the load centers, and the voltage level can be properly adjusted to be applied to facilities. There are two main types of power transformers, one is oil-immersed transformers, which has the advantages of good insulation properties, good thermal conductivity, and high reliability; another one is epoxy resin transformer, which has the advantage of good moisture/fire resistance, small size, and easy maintenance. The semiconductor industry is key industries in Taiwan, and it is a highly load-density, high power quality, and high energy-consuming industries. In addition, Taiwan is narrow and humid, so the epoxy resin transformer is broadly adopted due to the good moisture/fire resistance and the small size. The reliability of epoxy resin transformer and the operating efficiency of the semiconductor industry is closely related. Therefore, not only the server routine test of epoxy resin transformer in factory is very important, but also the maintenance strategy is also one of the means to maintain the high reliability of the transformer. However, past observations indicate that the traditional maintenance strategy could not meet the needs of the semiconductor industry; there are still sporadic incidents of transformer. Therefore, the semiconductor industry introduces various on-line insulation diagnostics, and the maintenance strategy is gradually changed to condition-based from time-based maintenance strategy. The condition-based maintenance shows good performance. However, the risk of cost and testing costs differs between different industries, and the adopted maintenance strategy is also different. Thus, this study takes real cases as examples to identify the relationship between costs and risks. Then the operators can determine their own maintenance strategy, which best suit for their conditions.
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