Although some parts of the network are already electrified, the project will see the conversion of up to another 1,300 km of the Danish main line. Denmark’s governmental rail body, Banedanmark, is overseeing the electrification of the railway. The contract to carry out the works was awarded to a consortium of rail supplier Siemens Mobility and infrastructure contractor Per Aarsleff. The electrification programme began in 2014 and is due to be completed in 2029, when the current electrification contract expires. The electrification programme itself is mainly state-funded.

Part of its scope is to electrify Ringsted-Femern Banen, which is an infrastructure project for a new double-track railway from Ringsted to Rødby. This project is financed through Femern, as a part of the Fehmarnbelt connection project, a new 18 km road and rail tunnel expected to be completed in 2029 that will open up a new corridor from the Mediterranean area all the way to Scandinavia. This corridor will serve as a physical connection between Germany and the eastern part of Denmark, which also allows for faster transit to Sweden and further North.

Preparatory works before electrification                  
Electrification of the existing railway carries with it several issues that either need to be analysed or to be performed before actual electrification can begin. Banedanmark refers to these as preparatory works. This includes:

• Studies of possible environmental impacts of an electrified railway.
• Expropriation of necessary land, both municipal and private.
• Infrastructure adjustments: bridges which cross the railway will need to comply with the height of the catenary system being installed. In certain locations the railway track itself will need to be lowered; in other places the bridges will be altered, and in some places new bridges need to be built.

Electrification works                  
The electrification itself is primarily connected to new foundations along the railway tracks. The purpose of the foundations is to hold steel masts that will be installed into them. Subsequent suspensions are mounted on the steel masts, which must carry, amongst other loads, the contact wire, which provides power to the train’s electrical motors. Once all installations are complete, several tests are conducted to decide if the catenary system is ready for commissioning.

In order to disrupt commuters as little as possible, which is always the aim, these works are primarily performed in single-track possessions during the night.

The sections that will be electrified will be supplied with the Siemens SICAT SX catenary system, a further development of an existing catenary system. SICAT SX includes a staggered arrangement of contact wire and messenger wire, in which they do not run aligned, but rather in a zig zag pattern. This makes the installation less sensitive to wind, and this combined with a higher tension force means that the distance between masts can be almost doubled compared to previously installed catenary systems in Denmark.

The SICAT-SX system allows spans of up to 109-metre intervals between masts and 2 km tension lengths, reducing the required electrification equipment. Previous electrification in Denmark only allowed spans of up to 60 metres between masts.

Furthermore, SICAT-SX is also designed to deliver higher speeds – up to 250 km/h, as opposed to existing catenary installation types in Denmark that are only approved for 200 km/h.

Power to the railway                  
In Denmark, the electrified railway operates on 25 kV at 50 Hz. Power is supplied from the public supply network to substations that the electrification programme is building along the railway. The number of supply stations required varies from section to section; for example, two supply stations are planned in the approximately 140 km-long section between Aarhus and Aalborg, which is the current focus of electrification.

The role of the supply stations is to transform the voltage from the supplier’s 132 kV or 150 kV supply to the track’s operating voltage (25 kV). From the supply stations, voltage is fed to the track in both directions. After feeding trains with the required power, the rest is returned to the supply station via the rail.

Prior to electrification, analysis examined future power needs, how train timetables would evolve and the types of equipment that the operators were likely to put in operation. Once all of this had been considered, supply stations and transformers were dimensioned accordingly.

Autotransformers (AT system)                  
The need for supply stations is reduced because autotransformers (AT systems) are also being built. The AT system transforms 50 kV to 2 x 25 kV. An earthing point is inserted in the transformer coil, so that 2 x 25 kV is generated in opposite phases (+25 kV and –25 kV). The positive phase is connected to the catenary system, and the negative phase is led in an independent conductor on top of the masts, whereby the effect (power) can be transmitted close to the train’s position.

Operation of electrical trains is powered by AT systems from both sides. This reduces transmission loss (producing a more efficient transmission of power), which also means that there can be a longer distance between supply stations. This is important, since supply stations are typically placed close to the power supply, but the national energy system limits the number of locations in which Banedanmark can build supply stations.

Interface projects                  
As previously mentioned, the decision to electrify the main line railway has enabled the possibility to increase speeds. However, local topography affects speed increases. To reach the desired speeds, it has therefore been necessary to both renew railway tracks and upgrade the track accordingly.

With the spread of electrified rail track comes an increase in the number of operating trains and total electrical load. In order to ensure that the current line can keep up with the development, a separate modernisation project is working on upgrading and building new distribution stations, as well as sectioning the line into smaller sections with new feeding points for power supply.

• Further reading: Hitachi Rail unveils battery hybrid train for travelling between electrified and non-electrified sections of track.  
• Siemens promotional video about the SICAT SX system used in Denmark: