Capability of synchronous machines to ride through events with high ROCOF

Abstract

© 2019. The Author(s). The transition of power grids to implement large amounts of nonsynchronous renewables reduces the inertia in the power system. Therefore, the rate of change of frequency (ROCOF) after a fault of given energy is higher in low inertia grids than in grids with mainly synchronous machines operating. Standard faults for the design of existing synchronous machines assume fixed frequency grids, in which an electrically close fault happens. It is not tested, if the machines can ride through transient disturbances with high ROCOF. For ROCOF values of up to 1 Hz/s as foreseen for the upcoming grid code of the Republic of Ireland and up to 2 Hz/s for Northern Ireland, a thorough verification, if generators are capable to ride through such events is necessary. For this study, ROCOF frequency traces provided by the transmission system operators (TSOs) of Ireland were first benchmarked with a full-grid model and in a second step impressed on a model of generators connected to the power grid via a step-up transformer to study transient stability and nonlinear response of the generator. This paper focusses on the ability of nine different synchronous machines to stay connected to the transmission system during severe ROCOF events without losing synchronism.