Voltage Stability Assessment and the Need for Multi-Time Scale Dynamic Simulation

Real power systems exhibit dynamics that evolve across various timescales, with some phenomena occurring quickly while others unfold slowly. Historically, encapsulating all these dynamics within a single model has been impractical due to limitations in computational efficiency and modeling requirements. Therefore, when developing models for fast components, slow states are typically treated as nearly constant during rapid transients. Conversely, when simulating slow phenomena, fast states are assumed to be constant and thus neglected. This approach relies on time-scale decomposition, effectively achieved through an analysis known as singular perturbation. Long-term voltage stability serves as a pertinent example where, for practical reasons, transmission system operators often neglect fast dynamics and rely solely on static methods. This paper challenges this paradigm by demonstrating the risks associated with overlooking fast dynamics in long-term phenomena. The need for multi-timescale simulations is highlighted, particularly in modern networks that experience increasingly rapid dynamics.