Replacement of aging power transformers considering system risks under multi-level load

With an increasing number of installed power transformers have entered aging stage, the retirement timing becomes a major issue for power utilities because of their huge reinvestment cost and key roles in the reliable power supply. In this paper, a cost-benefit analysis method is put forward to decide the replacement decision-making problems for aging power transformers by considering system risks under multi-stages of the load. First, load factors under each load level are derived from the standard optimal load flow results. Then, annual expected energy not supplied (EENS) is calculated with non-sequential Monte-Carlo method. Last, risks decrease benefit and net reinvestment cost is considered to make a good decision of retirement for aging power transformers. The IEEE 24-bus reliability test system is employed to demonstrate the effectiveness of this method, and several interesting conclusions are obtained from case study results.