Improving the reliability of the “Nordbalt” electricity link between Lithuania and Sweden
The 450 km-long “NordBalt” link between Lithuania and Sweden was the world's longest offshore electricity transmission cable at the time of the project. However, High Voltage Direct Current (HVDC) technologies are developing rapidly. Currently, the longest HVDC cable runs between Great Britain and Denmark - the “Viking Link” (740 km). Nevertheless, diagnosing potential faults in cables of this length remains a major challenge for professionals today.
According to Mindaugas Kripas, the Head of “Litgrid” High Voltage Direct Current Interconnection Division, without automatic fault detection equipment, the preliminary location of a cable fault is calculated mathematically using existing data from the inverter’s control system, which is not accurate.
In this case, it can take up to two weeks to accurately detect and repair a fault at sea. The cost of renting a vessel for this purpose would be €200 thousand per day. Finding and fixing a fault in a land-based cable could take up to one week, and one day of “NordBalt” inactivity could cost up to €85 thousand.
“The equipment, which would not only immediately make us aware of a fault, but also the exact location of the fault, would be an effective investment that would allow us to shorten the time needed to fix a potential fault and reduce operational costs and potential losses,” says the representative of “Litgrid”.
In order to make high voltage direct current links such as “NordBalt” as reliable and affordable as possible, European Association of Transmission Operators ENTSO-E recommends the installation of automatic cable fault location equipment.
This is particularly relevant as “Litgrid” prepares to build a second offshore cable, “Harmony Link” with Poland, which will stretch from Darbėnai to Žarnowiec and cover about 330 km.
According to M. Kripas, as the number of underground and submarine cable lines in the world grows, so do the methods for locating cable faults. An innovative approach can help to identify the most appropriate strategy for cable lengths such as “NordBalt”.
An analysis of the solutions currently offered by different manufacturers, such as an underwater structure protection system and an acoustic sensing system, has shown that these systems are more useful to protect against failures caused by third parties. And while one of the alternatives was designed to detect various types of faults in real time, it consists of two devices that would need to be installed at both ends of the connection.
The “HiRES Locator” manufactured by “Highvolt”, a German manufacturer, was found to be the best option: “It is a universal device that records and analyses faults for both underground and offshore cable diagnostics.
However, the manufacturer recommends this device for 200 km long cables, so we decided to run an experiment to see if we could use it for the “NordBalt” cable. At the other end of the link, in Sweden, we will simulate a fault to see if the equipment can detect and locate the fault. If the trial is successful, we will consider buying the equipment and working with it.”
