Synchronisation Control Action for Very Low-Frequency Oscillations

Very low-frequency oscillations have been occurring on power grids with a high concentration of hydro generation and islanded grids with a lack of AC interconnection. These oscillations can persist in an ambient form or be triggered by a transient event before growing to the extent that threatens system stability. When a severe event occurs, it is important to identify the cause and have practical control actions to restore power system stability. Firstly, this paper demonstrates that synchronising a generator with a positive damping torque component can restore positively damped conditions. Simulations on a modified 2-Area system are evaluated with DIgSILENT PowerFactory. A transport delay is added to speed feedback of a GAST model governor to simulate a spontaneous negatively damped very-low-frequency oscillation with the appearance of being self-excited after a generation load imbalance. Secondly, a 300 mHz 0.08 Hz very-low-frequency oscillation on the Irish electrical grid is analysed using the governor based dissipation energy flow method. Dissipation energy flow is used to illustrate how the synchronisation of 2 generators successfully returned Ireland’s power system to positively damped conditions.