Masts failed and prevented emergency calls: How the people of Bornholm lost mobile phone signal due to power outage

Mobile phone masts rely on electricity to provide coverage. Therefore, things went awry on Bornholm. Illustration: josefkubes / BigStock

When Bornholm was hit by a prolonged power outage in February, the first inhabitants already lost their mobile coverage within an hour.

This is evident from a statement from the telecommunications companies to the Regional Municipality of Bornholm, which the Engineer has received.

The more than six-hour-long power outage started when an anchor of a ship severed a submarine cable to Sweden on the morning of 26 February. The power outage also affected the mobile phone masts and Bornholm Police has confirmed that the lack of mobile coverage made it difficult to get hold of the public-safety answering point.

The first connection is lost

Both Telia and Telenor, which share masts through the TT network, as well as TDC have installed backup power devices that can supply power for two hours on most masts. But before the first hour had passed, three of TDC’s masts were out of commission.

This meant that around seven percent of the telecommunications company’s total 17 000 customers lost their mobile coverage. By the time two hours had passed, the power was out on 12 masts and about 28 percent of the customers were disconnected.

“There are a few facilities, including some indoor facilities, that have not installed backup power devices and therefore lost coverage faster than the two hours,” confirms Youness Quriou, vice president of TDC NET Operations.

It was even worse for the customers of telecommunications company 3, whose masts only have backup power that lasts between 30 and 60 minutes. Therefore, after the first hour of the power outage, all 20 of the company’s mobile phone masts were out of service.

Here is the supplied material on how the power outage hit TDC’s masts.

Illustration: Bornholms Regionskommune

“We have the same standard for backup power in the whole country, so we ensure that all our masts throughout the country can be used if power goes out. We cannot predict where a power outage will occur geographically, and therefore we cover the entire country with the same emergency preparedness,” reads an email from 3, in which the company also points out that it is the authorities’ responsibility to ensure a stable power supply.

Two mobile phone masts left

In a Danish context, the power outage on Bornholm lasted a very long time. When the connection to the rest of the power grid is cut on an island like Bornholm, the local utility company is responsible for keeping the island running until the cable is in operation again. To avoid overvoltage in the power grid, the local energy sources must be started up slowly.

The graph submitted by the TT network shows the number of hours the masts were down.

Illustration: TT-netværket

The consequence on Bornholm is that more and more masts ran out of backup power during the power outage, and customers all over the island using all telecommunications companies lost the connection.

It is not clear from the material that the TT network has submitted to the municipality when the various masts failed. In the very last hour before power returned, only two masts were still in operation on the whole island. Both masts belonged to the TT network and were located in Rønne.

“It is our understanding that power returned at different speeds and thus the need for our backup systems was also different. This means that the time that an individual site was offline depends on how fast the power came back on and whether the backup system had enough reserves left to be able to stay online,” writes Jesper Mølbak, network expert at Telenor in an email to Ingeniøren.

Hardware fault at TDC

Even when the local utility company Bornholms Energi & Forsyning had its energy sources up and running and the power had returned to the island, there were still problems with mobile coverage.

Namely, there was a hardware fault on six of TDC’s masts, and while the rest of Bornholm’s population had regained coverage, 10 percent of TDC’s customers still did not have a signal.

“It is correct that six of our sites were affected by a hardware fault, which required new equipment, and that a technician had to be transported to Bornholm to solve the problem. For security reasons, we are unable to elaborate on the hardware fault. All sites, including those with hardware faults, were up and running again just 18 hours after the submarine cable was severed,” Youness Quriou explains.

Telecommunications companies promise improvements

Bornholm is particularly vulnerable to prolonged power outages due to its dependence on the submarine cable to Sweden.

Thus, the telecommunications network is also more exposed, and this is not the first time that a power outage has put the island’s telecommunications out of service. Namely, there is no requirement that the mobile phone masts must be secured against prolonged power outages in the agreements on spectrum licenses that the state enters into with the telecommunications companies.

Therefore, the emergency services on Bornholm have set up a working group, which is to find a solution so that the people of Bornholm do not lose the connection to the public-safety answering point during potential future power outages.

Both TDC and the TT network are also set to find a solution to the problem. Both point out that the local utility should put mobile phone masts first as critical infrastructure so that they are among the first to receive electricity after a power outage.

Bornholms Energi & Forsyning has, however, previously explained to Ingeniøren that it does not prioritize vital consumers when restoring the power. To avoid an overvoltage, the power is sent to the parts of the island where the demand matches the restored capacity.

Critical infrastructure such as the hospital and the airport are instead kept running by local emergency generators.

The TT network is also considering the possibility of upgrading several sites to have first priority, just as the two that stayed online in Rønne and had backup power for a longer period of time. However, the telecommunications company also points out that it will be extremely costly if the telecommunications companies themselves are to be responsible for maintaining the connection in all conceivable situations.