Broken subsea cable

Up to a year to replace broken Lewis and Harris electricity supply cable

22 October 2020

Many electricity cables run underwater to island communities

A brand new submarine cable is required to secure electricity supplies for Lewis and Harris.

Installing a replacement could take up to a year said SSE.

The existing 33,000-volt link from the national grid to the northern part of the Western Isles was knocked out on Friday, resulting in a major power cut.

The fault has been pinpointed to a section in the middle of the Minch, half way between Skye and the Bays of Harris.

Scottish and Southern Electricity Networks (SSEN) Distribution confirmed it has is launching the process for an end-to-end replacement.

Based on the depth of the water at the fault location, which is over 100 metres, 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.

SSEN said it reassured the local community that there is no impact to the supply of electricity to homes and businesses as a result of the fault. 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.

As part of these plans to ensure a continued supply of electricity to customers, 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 this August and 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 know how important a safe, secure and reliable supply of electricity is to our customers and we’re acting as quickly as possible to progress this significant cable replacement project.

“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.”