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New study suggests twin underground system cheaper in long run

Wednesday, 15th October, 2008 9:20am

Story by John Donohoe
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Campaigners opposed to EirGrid"s plans to build a network of electricity transmission pylons across Meath have published a report claiming that an underground system would be cheaper, more reliable and quicker to repair.

The North-East Pylon Pressure group (NEPP) last week published its own independent study comparing the merits of overhead lines and underground cables as part of its campaign to resolve major questions about the EirGrid proposal to string 140 kilometres of high power lines across the county.

The report, carried out by a leading German firm of consultants in electricity generation and transmission, Askon Consulting, based in Leipzig, recommends that EirGrid"s proposed power lines should be put underground all the way from Meath to County Tyrone.

The Askon experts say that parallel underground alternating current (AC) cables are cheaper over the longer term as well as more reliable in operation and quicker to repair. The report recommends using two parallel underground systems consisting of three aluminium cables, 1.4 metres beneath the surface. The maximum total area required would be 7.8 metres wide and 1.4 metres deep.

NEPP says that the Askon study is the first and only project-specific analysis of the comparative merits of underground cables and overhead lines for the proposed North-South interconnector.

'Askon framed their study entirely within EirGrid"s published benchmark criteria - affordability, reliability, safety, efficiency and security,' a spokesperson said. 'Unlike the Government"s Ecofys report - which was just a desktop, theoretical exercise - the Askon Consulting experts made an extended site visit to Ireland and their report is specific to a viable route and to the conditions in the north-east of Ireland.'

The author of the study is Professor Friedhelm Noack of the University of Technology, Ilmenau, Germany, who is one of the world"s leading experts on high voltage and low voltage electricity grids. Askon is part of the Altran Group, which employs 17,500 people in 20 countries. The study runs to more than 250 pages and is divided into two reports.

The study by the German experts also highlights that developments in high-voltage underground cable technology over the past 20 years have made it a viable alternative to overhead lines.

Compared with the proposed single overhead line, the decisive advantage of a parallel underground cable system is that it is operationally available for longer and is more secure and reliable in a national electricity grid.

The proposed single 400kV overhead line does not meet the internationally recognised criteria for assessing operational performance and reliability in a national grid (the so-called 'N-1 Criterion") in the event of a single component failing, but a parallel underground cable system does, Prof Noack argues.

In the case of a forced or planned outage, no electricity can be transmitted through an overhead line, but a parallel underground cable system can immediately take most of the load from a damaged cable.

Overhead lines fail much more than underground cables, the report states. Statistical data and statistical reliability analysis confirms that the probability of an underground cable failure is very low. The chances of both underground cables being unavailable are 1 in 100,000 years.

No 400 kV underground cable anywhere in the world has failed. Even if failures occur, they are quick to locate and fix; taking days rather than weeks. Outages caused by lightning strikes cannot occur in underground cables, Askon goes on.

While the investment cost of constructing an underground system is three to four times higher than overhead lines, over the 40-year life-cycle of the lines, this difference is cancelled out by much higher losses of electricity in overhead lines. Electricity losses in an overhead system are nine times higher than underground, the report says.

An underground system will save approximately six to 11 megawatts of generating capacity, thus saving investment and running costs and reducing the carbon footprint.

There are other considerable real economic costs that must be added to the cost of overhead lines - for example, loss of value in both housing and agricultural land. Taking these into consideration means undergrounding is the lower cost option, Askon argues.

On behalf of NEPP, Dr Colin Andrew said: 'The Askon report provides us with the conclusive results we need to influence the policy and decisions of the Minister for Energy, Eamon Ryan, to inform Government policy and to win the support of all the political parties. In that way, the proposed electricity transmission project may be completed in the only way that serves the national interest - underground. The time for research and talk from politicians is over. Now, the people of the north-east demand action.'

Dr Udo Hass of Askon added: 'Our report clearly demonstrates that there is an unanswerable case for implementing the proposed North/South transmission system as an underground cable option.'

Reacting to the report, Tomás Mahony, EirGrid project engineer, said the company will carefully study NEPP"s report and that the project team would be available to meet with the group to discuss it in detail. 'It is important people remember what international experts, EcoFys, said in their independent report on electricity transmission infrastructure published in July,' he pointed out.

'The report said nowhere in the world are there underground cables of the lengths required for the proposed 400kV power lines. Underground cables of the length we need are not technically feasible to build. No-one has done it anywhere else in the world and 97 per cent of similar transmission lines in Europe are overhead. Underground cables can be unavailable for periods of 10 to 100 times longer than overhead lines which would result in a less secure power supply,' Mr Mahony said.

He said it is EirGrid"s role to ensure the needs of the country are met with a safe secure and reliable power system. 'We cannot take the risk of putting in place unproven technology. It is our crucial responsibility for the development of Ireland to ensure that we have a secure system in place which creates the economic environment for local regions in terms of attracting industry thus creating jobs. This is critical infrastructure for the development of the north-east.'

Simon Coveney, Fine Gael"s spokesperson on Communication and Natural Resources welcomed publication of the report. 'This report is a major contribution to this discussion and should be taken seriously by the minister and by EirGrid when making future decisions on electricity grid infrastructure across the country,' he said. 'Fine Gael will be studying the report in detail, in the context of the need to upgrade Ireland"s electricity grid infrastructure.'

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