Sub-synchronous Resonance in the Irish Grid


EirGrid operates and develops the electricity system in Ireland. With a commitment of meeting 70% of Ireland’s electricity demand​ from renewable resources by 2030, EirGrid is making significant developments to its grid to ensure the wind and other renewable generation in the west of Ireland is transferred securely and efficiently to the east. One such development is EirGrid’s plan to install series capacitors to increase power transmission capacity and stability of the 400kV lines from the Shannon Estuary in the west of the country, to Dublin in the east.


Whilst the installation of series capacitors can bring significant benefits to an electric power system, their installation needs to be carefully considered. One well-known issue is that they can create a sub-synchronous resonance (SSR) between the capacitors and any nearby generators. This could potentially result in equipment fatigue and/or damage. As EirGrid’s first series capacitor project, the utility recognized the gravity of introducing new technology and understanding its potential grid-wide implications.


Investigating SSR requires specialist studies that a utility would normally only carry out if and when the need arises. As the proposed installation represents EirGrid’s first series capacitor project, the utility engaged the services of PSC. PSC undertook detailed power system studies of the Irish electricity network and its generators to fully evaluate the SSR implications and pass on the knowledge to EirGrid’s engineers.


PSC’s role was to:

  • Work with EirGrid to obtain generator models required for the study of SSR
  • Create models of the network and generators for studying SSR in PowerFactory and PSCAD
  • Develop a tool for performing the SSR studies in PowerFactory, and assist EirGrid’s staff in the operation and use of the toolkit
  • Undertake SSR power system studies in both the time domain using PSCAD, and the frequency domain using DIgSILENT PowerFactory
  • Develop an evaluation criterion for assessing SSR impacts in the Irish grid issues and PSC has been supporting EirGrid in mitigation plan discussions with local generator companies.

Additionally, as EirGrid continues to develop the series capacitor project, PSC has been assisting EirGrid in its discussions with series capacitors vendors. PSC has collaborated with EirGrid to create a vendor specification for the level of SSR mitigation required, and the system studies a vendor must produce to prove the mitigation.




Transmission and Distribution



“The SSR specialist studies provided by PSC engineers helped us better understand and plan for the implications associated with adding series capacitors to our network.”


Technical Lead, EirGrid