Ocean Kinetics - The Engineering Experts

Letters / A fact check of SSEN’s cable reliability claims

In the midst of the current Public Relations barrage by SSE, comments were made by SSEN Transmission project director John Scott about the Shetland – Caithness sub-sea HVDC cable and forecasts of 99.8 per cent availability were made.

Subsea cable very reliable, says project director

The following information may be of interest about recent issues surrounding subsea cables.

The confidence of the SSE spokesperson may be somewhat misplaced. At least [subsea cable supplier] NKT are very experienced in repairing cables!

Caithness – Moray HVDC Cable:

SSEN Transmission quote: “In our experience with the Caithness to Moray cable – the most directly relevant one, which we installed in 2018 – we had no issues at all with the cable being damaged or being out of service.”

The actual facts about this cable:

Scottish Hydro Electric Transmission Plc (SHET) have developed a High Voltage Direct Current (HVDC) electricity transmission link between Caithness (Noss Head) and Moray (Portgordon), collectively known as the Caithness HVDC Reinforcement (C‐M) project. NKT commissioned the cable which was laid in late summer 2017.

In early 2018, information became available that suggested there was a fault in the (offshore) installed cable. The location was identified as being at KP 13.158 (approximately 13 km from Port Gordon landfall). A cable repair and associated activities were undertaken by NKT in early 2018.

Further to these works it is now understood that a new Marine Licence for a series of additional works associated with identified areas of cable faults and required cable remediation is needed. The cable eventually became operational later in 2018 but has yet to operate at full capacity as output from Viking is planned to go through this cable as well.

Western Link HVDC cable outages:

A fault in the southern land cable on 19 February 2019 resulted in an outage until 22 March. A further extended outage from 6 April 2019 was caused by a fault in the undersea cable.

A third outage commenced on 10 January 2020, leading to Ofgem investigating. A fourth outage lasted from 15 February  to 13 March 2021. Results of the Ofgem investigation have yet to be made public.

These outages resulted in significant constraint payments having to be made to wind farm operators.

BritNed HVDC cable outages:

Press Release 8 July 2021: NKT completes offshore repair of the BritNed interconnector. For the second time this year, NKT has repaired the 450 kV HVDC power cable system BritNed after an outage due to a fault with the cable system caused by external impact.

Orkney – Pentland East cable:

This cable was replaced in late 2020 and the announcement of the completion of the work was welcomed with much publicity from SSE and others. However about 2 months later it was very quietly announced that the new £30 million cable had unexpectedly failed.

There is no word on whether or not it is to be repaired, as the old one was reconnected, at considerable expense. We can only assume that the cable failure was catastrophic.

Western Isles:

A cable to the Western Isles failed in October 2020 which resulted in considerable inconvenience and cost to local renewable energy generators. It has taken until August 2021 to get the cable replaced.

Offshore wind:

Concern over outages in cables connecting the UK’s offshore wind farms to the onshore network have been laid bare by the company that owns the link to Gwynt y Môr wind farm, which argues that a series of repair outages required following a cable failure in October 2020 should be underwritten by consumers because insurers are leaving the market.

The company notes that the cost of insurance has risen 40 per cent in the past two years and many insurers have declined to provide cover. Offshore wind farm cables have been under the spotlight for outages to repair cable problems, due to manufacturing faults, accidents and other issues.

In April this year, wind farm operator Orsted said it had put aside £350 million to repair or replace cables within its wind farms that had been damaged due to interaction with the sea floor.

It seems clear that subsea cables are very unlikely to be as reliable as SSE would have us believe. It is comforting to know that Lerwick Power Station will still remain ready to power up at a moment’s notice.

Frank Hay

Note: SSEN Transmission has been contacted for a response.