Reliability verification of a high voltage grid for urban operation

Operational challenges arise in urban high-voltage grids when maintenance and construction require the disconnection of multiple lines while ensuring high grid reliability. For this purpose, ewz, the distribution system operator of the city of Zurich, developed an optimization tool to evaluate the operational reliability of their planned 150 kV target grid. The tool employs a security-constrained DC optimal power flow model to analyze numerous line disconnection scenarios efficiently, identifying critical cases where line capacities are exceeded under the N-1 criterion. It supports the evaluation of strategies to mitigate critical cases, including leveraging grid flexibilities to reduce load, redistributing loads between substations, and reinforcing the grid. Results show that critical cases occur in less than 1% of the scenarios, and the proposed mitigation strategies can significantly reduce this number. The tool enhances planning and grid operation by identifying critical lines, facilitating simultaneous line disconnection scheduling, and proposing measures to improve reliability. This approach ensures that Zurich’s target grid meets the highest operational requirements, providing a robust framework for maintaining flexibility and reliability in the face of urban grid challenges. The tool’s ability to solve power flow cases within reasonable timeframes makes it an asset for grid operators.