Abstract: With the increasing penetration of renewable energy sources in power systems, requirements for system stability have become more stringent. Hydropower units play a crucial role in maintaining stable grid operation owing to their excellent regulation capability. As more pumped storage stations and large-scale hydropower plants come into operation, multi-field coupling－among hydraulic, mechanical, and electrical subsystems that share the same water conveyance systems－has become increasingly significant. Abnormal operation of a single unit may propagate its influence to the entire system via both electrical and hydraulic channels. However, the coupling mechanism between hydraulic interconnection and electrical interconnection remains yet unclear, and previous studies lack effective means for analysis of the dynamic characteristics of a hydro-mechanical-electrical coupled system. To address these problems, this study develops a steady-state and transient co?simulation method for the hydropower plant penstock system and the power systems, based on the alternating iteration concept and a partitioned solution approach, achieving coordinated boundary-consistent solutions between the hydraulic and electrical subsystems. On this basis, we construct a coupled transient simulation framework applicable to multi?unit shared penstock layouts. Integrating an IEEE 39-bus power network with two hydropower plants comprising four generating units, we examine the dynamic responses of the system under various disturbances—including three-phase short-circuit faults, load adjustments, and turbine load rejection. The results demonstrate our new method captures the interaction characteristics in the hydro-mechanical-electrical system with a good accuracy, effective and useful for stability analysis and control strategy design of such complicated systems.

Key words: water conveyance system, power network, hydro-mechanical-electrical-grid coupling, steady state simulation, transient process