Extending the operational capacity for HVDC exports on the power system of Ireland and Northern Ireland

摘要

The power system of Ireland and Northern Ireland is an independent synchronous system with HVDC interconnection to Great Britain (GB) via two HVDC interconnectors. The Moyle and East-West interconnectors provide a combined capacity of 1000 MW power transfer between the island of Ireland and Great Britain. The Irish system is currently undergoing significant change due to increased penetration of non-synchronous renewable generation. Policy objectives aim to have over 40% of total electricity consumption from renewables by 2020 with 37% coming from wind power plants. This will result in significant challenges for the transmission system operators (TSOs). One such challenge is managing interconnector flows to and from Great Britain and ensuring that system stability is maintained for all scenarios. A greater level of power export from the island of Ireland to GB has been observed at times of high wind generation. This poses a number of challenges for the system operators. System inertia is lower at times of high wind which makes the system frequency susceptible to larger changes in the event of a large energy imbalance. In addition, with power being exported to Great Britain there is a risk of an exceptional high frequency event if one of the interconnectors trips. Concerns related to exceptional high frequency events resulted in the TSOs introducing an export limit of 300 MW for an individual HVDC interconnector. The TSOs have recently engaged in a project to extend the export limitation to the full capacity of 500 MW for each of the HVDC interconnectors. To do this, the TSOs carried out analysis aimed at developing operational practices to ensure secure operation of the power system during times of high export. This paper outlines the analysis and subsequent actions undertaken by the TSOs to extend the HVDC export limit on the island. In particular, the paper presents study analysis which has led to the development of an 'Over Frequency Scheme' (OFS). The OFS is designed to sequentially shed generation across the island to prevent extreme over-frequency conditions.