Worked on the PowerGridModel/power-grid-model repository to establish the foundation for a new Power Grid Model project using C++. Focused on creating the initial project skeleton and branching structure to support future development. Enhanced error handling by refining transformer error messages, ensuring unique and sorted transformer IDs to address duplicate reporting issues. Expanded unit testing coverage to include complex transformer scenarios, such as three-winding transformers with multiple edges, improving reliability and clarity in error reporting. These efforts laid the groundwork for rapid feature delivery and reduced regressions, emphasizing robust error handling and comprehensive test coverage as core development practices.