The Influence Mechanism of Substation Transformer on Total Supply Capability (TSC) of Distribution Networks

The total supply capability (TSC) quantities load supply capability of a distribution network under specific security criteria. This paper develops and utilizes several quantitative tools, including the TSC curve, active transformer capacity, and boundary decomposition, to investigate the impact of transformers on TSC. It is found that the TSC curve remains unchanged if the transformer capacity is no less than the active transformer capacity, with only the feeder boundary taking effect. Otherwise, the TSC curve decreases due to the binding mixed boundaries, becoming deeper as the transformer capacity decreases. These rules and mechanisms are validated through case studies on urban distribution networks, enhancing the theoretical foundation of TSC and holding practical significance for security analysis. For instance, if the substation transformer capacity is larger than the defined threshold, security analysis can be simplified by ignoring transformer capacity constraints, and the transformer upgrade can be deferred in practice.