Contribution of Large Synchronous Turbogenerators to RoCoF Mitigation in Low-Inertia Grids

This paper proposes to focus on the following items:

Grid Stability and Rotating Inertia

One of the fundamental aspects of grid stability is the provision of kinetic energy. Historically and traditionally, the electrical grid has relied heavily on synchronous generators from coal, nuclear, gas or hydro power plants, which naturally offer kinetic energy due to their mechanical properties. Rotating inertia is essential for limiting and damping frequency variations in order to maintain grid stability during fast fluctuations in power supply and demand. However, the massive introduction of non-synchronous power park modules lacks this intrinsic kinetic inertia, leading to challenges in managing the Rate of Change of Frequency (RoCoF). Impact of Non-Synchronous Generators on RoCoF

Historically, RoCoF was not a significant concern for system stability of large interconnected systems because grids operated predominantly with synchronous generators.

As renewable energy sources increasingly contribute to the power grid supply, the current absence of inertia from inverter-based technologies can impact grid frequency variation rates when there is an imbalanced situation between power supply and power demand.

The current shift therefore necessitates a re-evaluation of grid dynamics. The reduced inertia in systems dominated by renewable energy production can lead to large RoCoF changes during major imbalances, affecting the grid's ability to maintain stable operations.

Despite these challenges, turbogenerators offer a positive effect by providing essential support to the grid. Their inherent ability to provide kinetic inertia and frequency support aids in limiting rapid frequency changes and thus mitigating their adverse effects. By remaining connected during major network incidents (such as system splits or generating unit trips), turbogenerators help to stabilize the network, thereby reducing the RoCoF observed during these severe events.

This capability is crucial in preserving grid reliability and ensuring a smoother transition to increased reliance on non-synchronous power sources.

Turbogenerators and RoCoF withstand Capability

The capability of turbogenerators to provide inertia and also appropriately address the power imbalance during RoCoF events ensures immediate support to the grid, mitigating the adverse effects of load variations.

Assessing the RoCoF withstand capability of turbogenerator units requires advanced simulations, as full-scale large RoCoF tests are currently impractical. Simulations allow for evaluating the ability of turbogenerators to adapt to varying frequency profiles and identify possible mechanical and electrical limitations. By modeling different scenarios, the appropriate behaviour of a given unit to support and withstand the grid transient can be demonstrated.

Future Outlook

As the global energy transition progresses, continued research and development are vital to optimize grid performance, ensure its stability and in the worst-case scenario prevent the grid collapse, while taking into account benefits and challenges posed by both turbogenerator units and non-synchronous generators.

The ongoing discussions around RoCoF mitigation and withstand capability of turbogenerator units and non-synchronous generators highlight the need for collaboration across industry, academia, and regulatory bodies. By fostering innovation and advancing simulation techniques, the energy sector can develop robust solutions to ensure a stable and reliable grid supporting the transition to a sustainable and low carbon energy future.