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NETWORK / 19 /JUNE 2017 D I G G I N G D E E P E R Running power cables deep below the ground offers operational as well aesthetic gains. While the use of undergrounding is becoming increasingly important to networks as they remove overhead lines from specific sites, a growing number of projects are digging deeper in order to transmit greater amounts of power. In these cases, networks are constructing tunnels deep below the ground so they can run high-voltage cables over long distances and transmit greater amounts of power to meet increasing demand. Completed in June 2016, three separate tunnels were successfully constructed beneath London by UK Power Networks to allow it to install state of the art 132Kv cables along a 5.7km route between south-east London and the City. Costing a total of £27 million, the project enables the network to transmit an extra 400Mw of power into the capital. Enabling it to continue to meet growing demand for power in the city, the project also built in space for extra capacity to be installed in future years. Progressing at a rate of 23 metres per day, a 91-tonne tunnel boring machine named Fionnuala was used to complete the final 3km stretch of tunnel that will connect substations north and south of the river. Removing the need to carry out works above ground along the entire route, the approach further reduces disruptions during its operational life with the cables remaining accessible when in need of upgrade or repair. Explaining the value of the project, Normal Kotecha, director of capital programme and procurement at UK Power Networks, says: "London's power needs are increasing all the time, and we are constantly investing in new infrastructure to ensure we maintain reliable electricity supplies. This essential project will increase the resilience of electricity supplies for residents and businesses for years to come." Offering the potential to take power transmission tunnelling to even greater levels, National Grid's proposal to construct a tunnel 13 miles long under Morecambe Bay would see a total of £1.2 billion invested to avoid any above-ground works being carried out in the southern part of the Lake District National Park. A key part of the proposed connection to join the planned Moorside nuclear plant in Cumbria to the grid, the tunnel would link up with an existing substation in Heysham in Lincolnshire. Also featuring 14.5 miles of underground cable, and 74 miles of overhead lines, the overall project would stand as the biggest investment in the country's electricity network for more than 50 years. However, due to ongoing concerns over the certainty of the nuclear plant being constructed, the National Grid has decided to pause the project. Such works have been enabled through the RIIO regulatory arrangement, with each network putting forward proposals to protect such areas by undergrounding their power lines and agreeing funding through Ofgem to pay for the work, with any added costs being absorbed through customer bills. By means of this mechanism, projects across the length and breadth of the UK are currently under way already or in consultation. Having agreed a total allowance of £7.7 million across its four licence areas for the eight year period, Western Power Distribution is in the process of completing undergrounding works to remove pylons from the Gower and Wye Valley and the Brecon Beacons National Park among other areas. Like WPD, Northern Powergrid is following through on its commitment by undergrounding 2km of cables in the north Pennines at a cost of £350,000. Beyond the extra costs they bring, the replacements will bring some benefits to the networks. Through a combination of being based on more modern technology and by offering shielding from both the elements and the interference of wildlife, the burying of the cables will bring operational improvements to the areas which they supply. Steve McDonald, head of programme delivery at Northern Powergrid, explains that the programme investment will result in the creation of a "new modern underground cable network to improve the quality and reliability of electricity supply for the local community". However, the shi" beneath will also bring new issues. In addition to the complexity and disruption of digging up ground to bury the cables, any faults in lines once installed will require excavations to first locate the fault and further works to fix them once located, driving up both costs and disruptions. Overall, though, the relative pros and cons of overhead compared with underground on individual projects are probably less of an issue than the fact that neither side of the debate is likely to be entirely satisfied. Those who campaign against pylons have already called for the practice of undergrounding to go beyond areas of natural beauty, while networks can only manage the extra costs up to a certain degree. Resolving this imbalance will be the main challenge, but SSEN and other networks are attempting to resolve it amicably, by involving those affected, and asking them to choose which pylons should go. N