Graph Theory-Based Topology Derivation for Diverter Switches of Vacuum-Type OLTCs

Vacuum-type on-load tap changers (OLTCs) are widely adopted in ultra-high voltage converter transformers to perform frequent voltage regulation without interrupting the load current. The diverter switch topology is the key basis of switching procedures and mechanical design for OLTCs. Due to the lack of an effective topology derivation method, the acquisition of diverter switch topologies with symmetrical features remains a long-standing challenge. In this paper, the diverter switch topology is abstracted as a weighted graph with designated external nodes based on graph theory. Meanwhile, a computer-aided topology derivation method is developed to obtain diverter switch topologies with given components. Specifically, according to proposed electrical criteria and transition function criteria, all possible topologies are enumerated to screen out feasible diverter switch topologies, among which structurally symmetric topologies are further identified. Graph generation, screening and identification are implemented with MATLAB code. The proposed method for automatic topology derivation can also be applicable to the structure design of other intricate power equipment.