This paper presents an approach for studying Very Low-Frequency Oscillations (VLFOs) between 0.03 and 0.08 Hz that have been observed on Irelands All-Island transmission system. Previous work by Ireland's TSO has found that the occurrence of the VLFO is linked to the generation dispatch of synchronous machines with governor control. This study verifies previous research by Ireland's TSO and analyses sensitivities such as inertia, system frequency and online generator status that causes an increase in VLF mode magnitude. This paper's results are based on 1-second resolution system frequency, metered generation and power system metric data from 1/1/2018 to 1/10/2020. This analysis demonstrates that the VLF oscillatory mode's stability is highly correlated if governors that consistently provide positive damping torque to the VLF mode are not synchronized. The findings from the study are demonstrated on several events on the Irish system using PMU data. The governor-based dissipating energy flow method is used to validate the relationships found from the generator status and system frequency case study.

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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 distributed energy flow method. Dissipating energy flow is used to illustrate how the synchronisation of 2 generators successfully returned the Irish power system to positively damped conditions.

This paper presents a novel and cost-effective solution for detecting the islanding condition at embedded generators using an innovative new type of phase angle detector, the "quasi-PMU". The method works by checking the synchronism of the embedded generator with respect to a robust reference location. The method is low cost, effective, and easy to configure using a modern broker based "one-to-many" solution for the telecommunications needs. The new "quasi-PMU" is validated against appropriate IEEE compliance standards and shown to be effective in detecting the islanding condition using data obtained by an experimental study and through simulations. The islanding detection method presented in this paper is particularly suited to grids with increasingly large dynamic events and frequency excursions arising from lowering system inertia. The authors' design gives the system operator confidence for consistent operation of embedded generation protection. The method is affordable, reliable and is ready for immediate implementation.

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