Optimal Transmission Switching as a Remedial Action to Enhance Composite System Reliability

Increasing redundant paths in transmission grids has always been thought to be a tool to enhance service reliability. However, network equations by intertwining power flows through redundant paths impose more limits on systems with more redundancy. Accordingly, autonomous removing of a few lines may relief capacity limit violations in some contingency events thereby enhancing service reliability. This paper aims to study impacts of manual removing of transmission lines on composite system reliability. For doing so, the existing model is extended to consider optimal transmission switching (OTS) as a remedial action. The model minimizes total damage cost imposed by load curtailments. The extended model is formulated in mixed integer linear programming (MILP) format that can be easily solved via commercial solvers. The model is applied to likely contingencies wherein violations in capacity limits are encountered. Then, the results along with occurrence probability of the contingencies are taken into use to calculate load point and system oriented reliability indices. Simulation results on the modified reliability test system (MRTS) demonstrate great enhancements in service reliability when OTS is realized.