A Practical Methodology for Determining the Retrofit Prioritization of Aged GSU Transformers

Generator Step-Up (GSU) transformers are critical equipment in composite generation and transmission systems, yet they are prone to aging failures due to long-term exposure to multiple stress factors. Therefore, the reasonable prioritization ranking of these aged GSU transformers is essential for timely and cost-effective retrofitting to ensure system reliability. In light of this issue, this paper presents a practical methodology that considers both the transformers’ contributions to system risk and their structural vulnerability when determining the retrofit prioritization of aged GSU transformers. First, the analytical formula for the unavailability of transformer aging failures is derived for system risk evaluation. Proportional sharing theory is then applied to calculate the allocated risk value for each GSU transformer, characterizing its contribution to system risk. Subsequently, the electrical betweenness of each transformer branch is calculated to represent its structural vulnerability within the system topology. On this basis, the fuzzy entropy weight (FEW) algorithm is employed to calculate the weights for both the system risk contribution index and the structural vulnerability index, establishing a comprehensive index that can be used to rank the retrofit prioritization of aged GSU transformers. Case studies are conducted on the IEEE RTS-79 system to illustrate and validate the effectiveness and practicality of the proposed retrofit prioritization ranking methodology.