Study on Operational Stability of the Hydro-Turbine Governing System for Three-Turbine Shared Tailwater Tunnel

As a key power source for peak regulation and frequency control, hydropower units frequently adjust their output to maintain grid stability. In shared tailrace tunnel systems, hydraulic coupling between units significantly influences system stability. This study investigates a three-unit system with a common tailrace tunnel, establishes its mathematical model, and employs linear stability analysis to examine its stability characteristics under small disturbances. The research focuses on the impacts of total power output and power allocation strategies on system stability. Key findings reveal that (1) the stable domain of each unit decreases with greater penstock water inertia, and the instability of any single unit propagates through hydraulic coupling, causing system-wide instability; (2) the control parameters of individual units primarily affect their own stability, with negligible cross-unit impact, and the system’s overall stable domain is determined by the unit with the smallest stability region when uniform parameters are adopted; (3) increasing the total power output reduces system stability, and equally distributing power among units is more conducive to stable operation than concentrating it on a single unit. These results provide a theoretical basis for the optimized dispatch and stability control of multi-unit hydropower systems with shared hydraulic structures.