I. Introduction
Operation of power system equipment under overloading conditions more often occurs in developing countries due to less transmission and generation resources. Overloading of a power transformer will accelerate its insulation aging, which reduces its physical lifetime and increases depreciation cost. Furthermore, the increased failure risk of transformer due to overloading may cause frequent interruptions and cascading outages in power systems. Therefore, it is essential for system operators to understand possible failure risk of transformers and its impact on reliability at each bulk load point in power system operation.