Reactive power boosting strategy for hydrogenerators: framework and evaluation using Nordic machine data

Modern power systems face operational challenges due to the integration of variable renewable energy, necessitating enhanced reactive power support from synchronous generators. In this study, we propose a comprehensive reactive power boosting strategy (Q-strategy) framework, addressing technical and economic challenges via four pillars: (1) Q-boost defines reactive power limits for continuous/dynamic states by leveraging thermal margins under insulation thresholds (155 °C); (2) Q-model, a capacity twin model (CTM) combining a lumped-parameter thermal network and saturated field current models, enables online hot spot temperature management without finite element analysis; (3) Q-energy optimizes reactive energy delivery by integrating thermal endurance models with aging and start–stop cycles; and (4) Q-value formulates costs for reactive power services, accounting for losses beyond grid codes and lifetime depreciation. The results demonstrate a 57% increase in continuous reactive power capacity, with smaller generators incurring higher costs (up to 1.33 $/Mvarh) than larger units. The proposed framework exploits hydrogenerators’ slow thermal time constants by using authentic historical machine parameters and operational statistics from Nordic installations. To isolate the machine’s direct electro-thermal boundaries and localized voltage-support capabilities without confounding multi-bus network variables, system-level validation is conducted on a single-machine, two-bus power system topology subjected to extreme contingency events and localized load profiles. An online temperature controller ensures safe operation under extreme conditions while aligning with real-world load patterns. The Q-strategy offers a cost-effective alternative to FACTS devices, balancing grid resilience with economic feasibility in high-renewable grids.