A two-stage overload strategy of oil-immersed transformers considering operation risk

Recently, the incentive to improve transformer utilization driven by increasing power demands and financial pressure of new equipment investment is more and more strong. Existing study focus on overloading constraints like hottest-spot temperature (HST) and failure rate, but the transformer operation risk is rarely considered in overload strategy making. This paper firstly proposes an operation risk analytical method of oil-immersed transformers, to evaluate the transformer loss, power grid enterprise loss and society loss during overloading. Considering the operation risk, a two-stage overload strategy is presented. In stage 1, the security constraints including HST, failure rate and the proposed risk are discussed to obtain a preliminary strategy; in stage 2, benefits and costs of overloading are calculated to analyze the economy of strategies between preliminary strategy and full-loading, and the profit-optimal strategy will be chosen as the final strategy. The validity of proposed overload strategy and influence of transformer service time on strategy making is demonstrated through case study.