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Denmark at risk of having all its submarine cables sabotaged at the same time


At the beginning of October, two Russian frigates and a few other Russian ships were spotted near the Danish island of Læsø. The Danish inspection ship “Thetis” was quickly dispatched to the location to patrol. Why would Russians be there just days after the sabotage of the Nord Stream gas pipelines near Bornholm.

Did they have malicious intents related to the important submarine cable laid on the bottom of the Kattegat between the town of Vester Hassing in Jutland and Lindome in Sweden?

The media rode a wave of fear, which grew even bigger when a fault on the submarine cable between Bornholm and Sweden soon after caused a blackout in Bornholm.

Although a couple of diesel generators could temporarily keep Bornholm running, the outage was a reminder that Denmark is highly dependent on its submarine cables and can suddenly end up in a major crisis of historical proportions if the cables are affected by faults or exposed to sabotage.

Growing vulnerability

And there is good reason to be nervous about what might happen next. At least that is the opinion of Claus Leth Bak, who as a professor at the Department of Energy Technology at Aalborg University researches electricity transmission systems and high-voltage engineering.

The Nord Stream sabotage clearly demonstrates that there is a “colossal risk” of easily performed sabotage of the infrastructure on the bottom of the sea, whether it be gas pipelines or submarine cables.

“After all, we are going to base an increasingly large part of our energy supply on electricity and gas that comes to us from the sea. We are becoming more and more vulnerable because we have critical infrastructure out there,” Claus Leth Bak says and points out that it is easier to sabotage cables unseen at sea because one can operate in the dead of night far out in the Baltic Sea or in the Skagerrak.

“If it’s possible to sabotage a gas pipeline, as we have seen happen recently, it’s just as easy to sabotage a power line,” he says and continues:

“The attack on Nord Stream has proven that those who did it were experts. They knew exactly what was needed. So they can, of course, also find the submarine cables at the bottom of the sea. There are maps that have been made available in order to avoid sailing over them, and they can be searched with magnetic-field-sensitive equipment.”

“Submarine cables are much easier to destroy by detonation, as not much explosive is required to make them short circuit. So, a coordinated attack on several submarine cables at the same time is a likely scenario—of course, because those who want to sabotage our power supply possess enough knowledge to know that a SIMULTANEOUS attack is critical.”

“The more you think about it, the worse it looks. Gas pipelines are extraordinarily strong structures of several-centimetre-thick steel + usually an outer concrete layer. It takes far more to blow up a gas pipeline than a submarine cable.”

Denmark has connected its power grid to several neighbours, such as Norway, Sweden, England, Germany, and the Netherlands. Is it a utopian scenario to imagine all cables being damaged simultaneously?

“No, not at all. Especially not in light of what we’ve seen with the gas pipelines. If you can blow up a gas pipeline on the seabed, you can do the same with a submarine cable to Norway and Sweden,” Claus Leth Bak says and continues:

“If the submarine cables that connect Denmark with the neighbouring countries are attacked in a joint action, we will very likely have a blackout in Denmark.”

Von der Leyen wants “stress tests”

This threat has now been recognized by the President of the European Commission, Ursula von der Leyen—a threat that applies to all member states.

A few days after the attacks on Nord Stream, she asked all member states to initiate stress tests of their critical infrastructure—stress tests which will be carried out by the authority responsible for the relevant link in the infrastructure.

Von der Leyen did not elaborate on what she meant by stress tests. And apparently, the responsible authorities have not yet been informed about it either. In general, there is not much that Energinet can say about it as the responsible authority for the submarine cables.

Energinet’s vice director Claus Winther reminds that Von der Leyen’s order is still quite recent.

“We are awaiting further details from the European Commission on what it expects us to do in addition to what we are already doing,” Claus Winther says to Gridtech.

Gridtech: Does Energinet have specific emergency procedures for what should happen if the power grid experiences a brownout or a blackout due to failures, sabotage, terrorism, or accidents? If so, what do they include?

“We have emergency procedures, but I cannot describe them for security reasons,” Claus Winther says. He says that the Danish power grid is designed to be able to cope regardless of which of its N components go down. Here, N covers all components of the electrical system, such as power plants, HVDC links, transformers, AC links in the form of overhead power lines and cables, and much more.

“The Danish power grid is arranged according to the N-1 principle, which means that it will be able to cope regardless of which of its N components goes down. Because the grid is so robust, it will also often be able to handle larger outages equivalent to N-2 or perhaps even more. We have historically handled situations worse than N-1 without it having been necessary to activate brownout,” Claus Winther says.

Is there an emergency plan for N-N?

“We continuously train for different scenarios,” he says and elaborates that the training consists of many elements, such as simulations and tabletop exercises that can take place internally in the company or encompass the entire sector.

“The incidents that the grid can handle are constantly changing and we constantly keep an eye on it. But we have procedures for brownout and black start, i.e. starting from scratch,” he says.

But blackout is not necessarily N-N—it could be N-3, if it e.g. includes the three most critical components?

“Geopolitically, Denmark is in a new situation. We have not built our infrastructure for times of crisis, but we are well prepared for different scenarios,” Claus Winther says.

Restarting the power grid is not straightforward

If a fault or a sabotage ends in a blackout, Energinet has to try to re-establish the power supply with whatever is available, Professor Claus Leth Bak says. And it will happen in several parallel stages since the Danish grid is split into several units, with Jutland and Zealand each having its own grid, DK1 and DK2, which are connected via the Great Belt, while Bornholm has its own small grid, which is connected to Sweden.

“DK1 would probably be brought to life via the overhead power line from Germany, if it is not also sabotaged. Zealand has cable connections to Sweden, but the cables across the country could be blown up by saboteurs at the same time.

And if these cables are gone, then there is nothing else to do but to start up the power grid as was done in the old days, that is, with the help of old power plants,” Claus Leth Bak says and points to the Nordjylland, Studstrup, Skærbæk, and Asnæs power stations as possible candidates for black start. In addition, there are older power plants that have been taken out of operation, but which may be able to be put back into use.

“Starting an old power plant is not something you can just make happen. You can’t just press a button. It can take several days, maybe weeks. It depends on how long they’ve been out of service,” Claus Leth Bak says.

Small steps

Either way, we would have to restart a completely dead power grid one piece at a time, wire by wire by wire, component by component. Otherwise, such a large transient builds up that whatever it is that powers the grid will not be able to handle it.

“Every time you connect a new component, there are some surges in the system. And if you connect too many at the same time, the surges become so large that the generators and other sources used to restart the grid cannot cope, and the entire grid becomes unstable during the recovery,” he says.

The reason we have to be so careful is that the transmission system is a meshed network. The lines are not drawn linearly from A over B to C, but between many nodes, which together form meshes with several lines to one node. It must be started carefully and gradually loaded. It must be connected piece by piece.

“Energinet has detailed plans for what to do if it happens and in what order. I know this because I myself worked at a power station many years ago. There are various operating instructions for how to bring the grid back to life if dies due to a specific reason,” Claus Leth Bak says.

A lifeline

While Jutland is relatively robust thanks to its HVDC submarine cables to Sweden and Norway—plus a connection to Germany—and Zealand also has a cable to Sweden, Bornholm is vulnerable because the island has no transmission network. Bornholm is normally only connected to Sweden with a single cable. If it is disconnected either due to fault or sabotage, there will be no power supply on Bornholm, and it will have to be re-established with Bornholm’s own power plant and diesel generators until the cable is repaired. There is no emergency solution.

Claus Leth Bak says that he and his colleagues are currently researching how wind farms can be used to restart a dead power grid. Such a solution could perhaps be suitable as an emergency solution on Bornholm, if the power grid could, for example, receive artificial respiration from the Kriegers Flak offshore wind farm—a solution that still needs to be worked on, since it turned out that the wind farm cannot be easily connected to Bornholm’s AC grid.

Such a manoeuvre requires a converter station.

“When you connect HVDC to -AC, it is often a connection to a large grid such as DK1 or DK2. But when it comes to the small grid on Bornholm, there are some technical challenges in connecting to HVDC plants. And as far as I know, those problems have not been solved yet,” Claus Leth Bak says and expresses hope that solutions to the biggest technical challenges will eventually come.

Critical condition

The scenario in which all submarine cables are taken out simultaneously is perhaps difficult to imagine. But it can still happen, Claus Leth Bak assures. Because the power cables were laid at a time when there was no war in Europe and there was less focus on security.

“If someone wants to attack us like that, they could undoubtedly succeed. In that case, Denmark would lose power and enter a critical state. It would have unimaginable consequences,” he says and continues:

“The latest Nord Stream incident is a game changer that forces us to rethink how vulnerable our energy infrastructure actually is. This applies to everything from electricity to gas and plants—whatever we need to be able to supply ourselves with energy.”

Illustration: Privat