Ireland's EirGrid on Dec. 18 submitted a planning application to An Bord Pleanála under the Strategic Infrastructure Act for the Meath – Tyrone 400kV Interconnection Development, which will facilitate cross-border sharing of electricity and ensure the long-term secure supply of electricity for the North East.

The route being submitted for planning approval runs from Woodland, Co. Meath to Lemgare, Co. Monaghan and includes a proposed new substation at Moyhill, Co Meath. This route was defined in earlier route selection studies as Route 3B from Meath to Cavan and Route A from Cavan to Tyrone.

In the course of examining options for this project and for the development of the transmission system generally, EirGrid has carried out extensive technical and economic analysis and has reviewed international practice and experience. One of the issues frequently raised is the possibility of developing an underground cable solution. Having carried out detailed analysis and having reviewed a wide range of international material, EirGrid has concluded that with the current state of technology it is simply not practical to develop an underground solution for this project today.

“Internationally there is a reasonable level of experience of underground development at lower voltages,” said Tomás Mahony, Project Engineer, EirGrid. He adds: “However at 400kV, the voltage required for this project, many of the technical challenges have not been overcome and there are no underground cable developments anywhere in the world at this scale and voltage. EirGrid concludes that attempting to develop this project on an underground basis would at best be a high-risk experiment, which may well result in failure, could waste many hundreds of millions of customer’s money and would jeopardise security of supply to the north-east region and indeed to the electricity system throughout Ireland.”

The analysis carried out by EirGrid includes a study by PB Power, which looked at the engineering, environmental and cost issues associated with undergrounding a project of this nature. The report concludes that overhead power lines are the cheapest and most secure option for the planned power lines in the North East. These findings are very much in line with a wide range of reports carried out internationally by transmission system operators and government authorities, including the Ecofys report commissioned by the Department of Communications Energy and Natural Resources.

EirGrid also commissioned Tokyo Electric Power Company (TEPCO), which has installed and operates the longest 500kV underground cable in the world at 40 km, to examine the potential for installing high voltage underground cable in the Irish system, ignoring cost and environmental issues.

The TEPCO Report confirms that there are a number of serious technical challenges involved in installing an underground cable of this type and length. EirGrid concludes, based on a review of the TEPCO report and other inputs, that there are huge risks which would accompany a project on this scale.

TEPCO is one of a suite of reports being published in conjunction with the submission of the planning application to An Bord Pleanála.

“EirGrid does not intend to propose an underground solution, which is clearly technically inferior, would cost at least hundreds of millions of Euros more than an overhead line solution and which ultimately may well fail, thus putting security of electricity supply at significant risk,” Mahony said.