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Scottish interconnector to take 12 months to replace

By: Tom Russell 23/10/2020 SSEN

Cables General Interconnectors

Following a recent fault to the 33,000-volt subsea electricity interconnector connecting Lewis and Harris to the Scottish mainland, Scottish and Southern Electricity Networks (SSEN) Distribution is now starting a project to undertake an end-to-end replacement of the subsea cable.

On Friday 16 October at 10.28am, SSEN was alerted to a fault on its network which temporarily interrupted power supplies to 13,600 customers on Lewis and Harris. Engineers immediately worked to restore supplies from Battery Point Power Station, with power restored to all homes and businesses by 12.26pm later that day.

Investigations, including location testing from each shore end, confirm a fault on the 32km cable, which runs from Ardmore, Skye to Beacravik, Harris around 15km from the shore on Skye. Based on the depth of the water at the fault location, which is over 100m, a repair has now been ruled out and a full replacement is required.

SSEN has initiated the procurement process to source a replacement cable, is reviewing the availability of cable-laying vessels and has undertaken preliminary engagement on marine licensing consents. The network operator is also reviewing all options to assess if the replacement will be undertaken on a like-for-like basis, or if the network can allow for a cable with greater capacity, whilst also meeting acceptable restoration timescales.

SSEN’s priority is to restore the network to normal operation as soon as possible. Whilst it is too early to determine specific timescales, SSEN expects the replacement project to take between 6-12 months given factors including cable procurement and manufacture, securing necessary permissions from statutory authorities and suitable weather conditions for cable installation.

In line with established procedures, Battery Point and Arnish Power Stations on Lewis will remain in operation for the duration of the fault alongside on-island renewable generation.

SSEN has increased deliveries of fuel via sea tankers to its on-island supplier to transport directly to the power stations. Further contingency measures are also in place, including the sourcing of large back-up mobile generation sets, to provide additional security of supply to homes and businesses on the islands.

As a result of the fault, there will be restrictions to electricity generation export during the period. SSEN remains in close contact with generators on Lewis and Harris to manage any generation constraint and will look to minimise disruption wherever possible. This includes undertaking a network study to understand any options to further increase the allowed generation.

An end-to-end subsea survey of the Skye to Harris cable was undertaken in August 2020 which did not identify any material concerns requiring attention. Further investigations are ongoing to determine the root cause of the fault, including to rule out any instance of third-party damage.

Mark Rough, Director of Customer Operations at SSEN, said: “We’d like to reassure our customers that our well-established resilience plans are in place to maintain power supplies to local homes and businesses as we source and install the new cable. Our power stations are designed and maintained to carry out full operations and play a crucial role to keep the power flowing during this type of situation.

“To maintain system stability, there will be restrictions to generation export until the network is restored to normal operation. We remain committed to exploring options and solutions to maximise the amount of renewable generation that can run and are undertaking one-to-one conversations with affected generators on Lewis and Harris as a priority.

“We have been engaging with local stakeholders throughout the week and met with Comhairle nan Eilean Siar this morning to provide a full update. A further meeting has been scheduled for next week to provide an update on progress.”

For more information on interconnector projects worldwide, click here

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Scottish interconnector to take 12 months to replace

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