Rail Baltica is northeastern Europe’s most important project, a high-performance railway line that will extend over 870 kilometres across the three republics, thanks to an investment of 5.8 billion euros and will create nearly 36,000 jobs. The project involves five European Union countries: Poland, Lithuania, Latvia, Estonia and, indirectly, Finland. It will connect Helsinki, Tallinn, Pärnu, Riga, Panevéžys, Kaunas, Vilnius and Warsaw. Described by the Transport Ministers of the Baltic Republics as the great economic recovery project, the truth is that the implementation of Rail Baltica involves a large part of the European railway engineering and construction sector, including Ineco, which to date has been involved in four projects that, in accordance with EU indications, are aimed at achieving technical compatibility of infrastructure, rolling stock, signalling systems and other systems and procedures for their full integration into the European railway network.

A SUSTAINABLE CORRIDOR. The new railway line will bring not only economic benefits, but also significant environmental and social improvements.

The Riga Ring, the most complicated urban stretch

The technical design of the 56-kilometres high-speed section through the city of Riga, the capital of Latvia, is the most complex stretch of the line since it passes through several densely populated municipalities and runs parallel to the rail corridor of the Latvian railways. Ineco and Idom were awarded this contract in July 2019.

The route is divided into three subsections (Design Priority Sections, DPS): Upeslejas-Riga Central (DPS 2); Tornakalns-Imanta (DPS 1) and Riga-Misa International Airport (DPS 3). Each of these has its own identity and completely different characteristics. DPS 1 is the most urban of the three sections, since it passes through the entire municipality of Riga, as well as areas with great heritage value. The route’s only tunnel is located here in DPS 1. DPS 2 passes through Riga and Stopini, which is less urban than the previous stretch. In this DPS, a major railway viaduct will be built over the Latvian railway circuit. Lastly, section DPS 3, the least urban of all, is characterised by intersections with various motorways generating multiple structures at these junctions. The project includes several improvements, including track alignment in order to achieve the highest possible speed in the different sections, as well as improved permeability and safety in the city of Riga by generating more than a dozen pedestrian crossings (in the form of walkways or underpasses) that are suitable for pedestrians, cyclists and people with disabilities. Road traffic in Riga will also be improved, thanks to the design of bridges and road junctions with a higher capacity. The project has a completion time of 24 months and is adjacent to the work recently awarded to Ineco in Northern Latvia.

With more than 600,000 inhabitants, Riga is the most populated city in the Baltic States, and its geographical location makes it a strategic enclave for passenger and freight transport. Located at the mouth of the great Daugava River, a few metres above sea level, the city is one of the most important economic and financial centres in the Baltic region. As a result, in addition to the fact that it is a UNESCO World Heritage Site, this city and its surroundings are a major attraction for the population, and the improvement of its railway network is vital for its economic and social development.

North Latvia, a long route through forests and wetlands

Ineco, in consortium with Ardanuy, will lead the design and supervision of the design during the construction of a 94-kilometre European-gauge stretch, which connects the city of Vangaži, northwest of Riga, and the border between Latvia and Estonia, in a contract worth almost 14 million euros.

The recently-signed North Latvia contract is one of Rail Baltica’s major railway projects and Ineco’s fourth for this ambitious new infrastructure in northeastern Europe, which will integrate the Baltic States into the Trans-European Transport Network (TEN-t).

The preliminary estimates for this section include, in addition to three stations, large and complex new infrastructure such as 36 road viaducts, 3 ecoducts and 16 railway bridges, including the viaduct over the Gauja River, the largest of all of the lines, with a total length of approximately 1.5 kilometres and more than 150 metres wide, for which the consortium will be joined by the firm Carlos Fernández-Casado SL, which is renowned for the design and supervision of large bridges and specialises in structures, some of which are among the longest in the world.

All the work that Ineco is carrying out for Rail Baltica is being
done with BIM technology

The scope of the work is divided into two phases, the design stage, with an estimated duration of 30 months, and the construction supervision stage, with an estimated duration of five years. Ineco will lead the project with the development of the entire railway section, in addition to the complete design of roads and geotechnical works. The entire project will be carried out with BIM, from the initial phases to study solutions and optimise the route, to the detailed design phases that will facilitate the execution of the civil engineering project.

Optimal electrification solutions

The planned substations are similar to this one located in Tábara (Zamora), Spain. / PHOTO_INECO

The study of the energy subsystem for the entire line was Ineco’s first contract with Rail Baltica. Awarded in consortium with Ardanuy, this is an in-depth analysis to assess the best available technologies and a design aimed at reducing life cycle costs.

The purpose of the study was to choose the optimal technological solutions for the different areas of the energy subsystem (traction, catenary and remote control substations), define how to tender the design and construction and specify the implementation strategy. This work gave Rail Baltica basic knowledge that will make it easier for it to deal with the upcoming design and technical assistance tenders.

Energy, step by step:

• Energy demand studies.
• Electricity power analysis and estimate for distribution networks.
• Traction substations, overhead contact line and energy control systems.
• Implementation and procurement plan.

Energy recovery improves the energy efficiency of the electric power supply installation for traction on conventional rail networks and reduces emissions into the atmosphere. Ineco’s first task was to draft the construction project for the installation of a regenerative braking energy recovery unit in the traction substation of La Comba in the province of Málaga, which was put into service in 2014. This is the only installation of its type in service on the conventional network (see ITRANSPORTE 44). The recuperator has made it possible to return more than 1 GWh/year to the power grid, representing an annual savings of more than 12.5% on the energy consumption of the Málaga-Fuengirola line, reducing CO₂ emissions by around 230 tons/year (based on a conversion factor of 0.23127 kg of CO₂ per kWh). The investment is expected to be recouped within a less than 10 years.

The success of this first energy recuperator prompted Adif to install recovery units in other substations. Since 2015, simulations on national gauge have been carried out to identify substations with the greatest capacity for energy recovery. Railway installations have been modelled taking into consideration data relating to rolling stock, traffic grids, geometric railway platform profiles, electrification installation characteristics, driving modes, etc.

The recovery of regenerative braking energy on the conventional network is one of the measures included in Adif and Adif HS’s Energy Saving and Efficiency Master Plans. It is also one of the energy efficiency actions included in the Programme of Subsidies for Energy Efficiency Initiatives in the Rail Sector (Resolution of 30 November 2015, BOE-A-2015-13117) offered by the Institute for Energy Diversification and Savings (IDAE). The funding provided by this body for the exploitation of braking energy covers 30% of the investment. Adif plans to have 12 new energy recuperators in service between 2019 and 2020, and is considering extending the installation of these units across its network, mainly on commuter lines.

Putting 12 new recovery units into service

The first simulations carried out by Adif in 2015 and 2016 on several conventional railway lines identified the substations of Alcorcón, Getafe, Guarnizo, Olabeaga, Martorell and Arenys de Mar as the ones with the greatest capacity for recovering energy and, therefore, the ideal candidates for the installation of recovery units. For these six installations, Ineco prepared the documentation for submitting subsidy applications to the IDAE (successfully awarded in January 2017), drafted the construction projects for the installation of the recovery units and is currently providing the works management and technical assistance. In 2017, Adif carried out a second series of simulations and selected the substations in Tres Cantos, Alcalá de Henares, Pinto, Leganés, Granollers and Castellbisbal. For these, Ineco also prepared the subsidy applications (successfully awarded in February 2018), drafted the construction project and will be providing the works management and technical assistance. It is expected that the first group of substations will be in service by mid-2019, and the second group by 2020.

These 12 recuperators are expected to save some 18.5 GWh/year, which represents a reduction in CO₂ emissions of close to 4,300 t/year and a financial savings of over 1.3M/year. With IDAE’s 30% funding, it is expected that the investment of more than 8M will be recouped in approximately 6 years. New simulations will continue to be carried out in the hope of further extending the installation of recovery units across the entire conventional railway network.

Theoretical basis

When trains use rheostatic or regenerative electric brakes, they transform the train’s kinetic energy into electrical energy. Their engines act as generators, slowing down the wheels and performing the energy conversion. Some of this energy is used to supply the train’s auxiliary services, and the rest, in the case of regenerative brakes, is transferred to the overhead line, increasing its voltage.

The first regenerative braking energy installation in the traction substation in La Comba has made it possible to return 1 GWh/year to the power grid.

Part of the energy fed to the overhead line is used by other trains that require it at the moment that it is regenerated, and the surplus is either sent back to the electrical grid if the traction substations are reversible (enabling a two-way transfer of energy: from the grid to the overhead line and vice versa) or it dissipates in the form of heat in the braking resistors installed on board the trains if the substations are not reversible.

Traction substations on high-speed lines use alternating current (AC), which means that they are reversible. However, substations in direct current (DC) electrification systems, such as metros, trams, conventional railway lines, etc., are not reversible because the change to DC requires rectifiers that only allow energy to flow in one direction, from the electrical grid to the overhead line.

The figure shows the general schematic for the energy recovery installation in the La Comba substation.

In order to make conventional substations reversible, a current inverter (DC/AC converter) must be installed in the substation, along with certain interface elements, such as DC and AC huts, wiring, electrical panels, control and remote control systems, etc. Together, all of these elements make up the braking energy recuperator.

The energy recuperator detects when there is a surplus of braking energy in the overhead line and allows the inverter to operate so that it can convert this electrical energy, in the form of DC present in the overhead line, into AC and feed it into the power grid.

The inverter load cycle

Ineco has collaborated with Adif on the selection of the load cycle of the inverters to be installed on its conventional network. Similar to other units installed in traction substations, such as rectifiers and transformers, the inverter must be a standard unit that can be installed in different substations on the conventional network, and not specifically designed for individual facilities.

Following the electrical simulations that resulted in the selection of the Alcorcón, Guarnizo and Olabeaga substations, information was made available to characterise the recoverable power.

The graph below shows a typical recoverable power profile. The peaks represent pulses caused by train braking whose amplitude, as well as duration and separation in time, is variable.

The parameters that characterise the pulses are: amplitude, duration of the pulses and time between braking.

To determine the load cycle of the inverter, defined as indicated below, the profile of dischargeable power was aligned with a sequence of pulses of constant amplitude, whose value is the RMS (Root Mean Square) of the instantaneous power values.

The inverter’s load cycle is defined based on the following parameters: maximum power (P_MAX), maximum power pulse duration (T₁) and cooling time (T₂).

An inverter with the specified load cycle must be able to permanently transfer every T₁+T₂ seconds a power pulse with the value P_MAX and duration T₁ seconds. To recoup 100% of the energy discharged by trains in the substation environment, the envelope of the inverter’s load cycle should contain all recoverable power profiles. However, the optimisation of the ratio of investment cost/recovered energy, that is, the maximum energy recovered for economically reasonable inverter dimensions, determined that the load cycle of the selected inverter will be determined by the following values: P_MAX= 2.5 MW, T₁= 40 s and T₂= 120 s.

An inverter with this power characteristic was able to recover the following percentages of dischargeable energy for the three simulations carried out for the load cycle determination study: Alcorcón substation > 73.15%, Olabeaga substation > 92.11% and Guarnizo substation > 99.97%.

A larger inverter would have made it possible to recover all of the available energy, but its cost would have made the investment unviable.

Another step in standardising the installation of energy recuperators was identifying the equipment that could be specified with precision, regardless of the specific design of the inverter by the technology company, in order to reduce the scope of supply of this company. This made it possible for energy recovery installations in different substations to differ only in the inverter and the equipment directly linked to its design, mainly DC and AC switchgears and filters, and transformers at the inverter output.

The design of energy recovery installations in conventional substations

Because there is a lack of free space inside substation control buildings, energy recuperators need to be installed in two separate buildings designated as the operations hut and the inverter hut. The operations hut houses the substation interface equipment and the inverter hut, the inverter itself.

An operations hut.

An inverter hut.

General schematic of an energy recovery installation

The general schematic of the energy recuperators to be installed in the substations of Alcorcón, Getafe, Guarnizo, Olabeaga, Martorell and Arenys de Mar (pictured) is different from the one implemented in the La Comba substation because the inverter can be connected in parallel to either one of the substation’s two rectifiers. This means that energy will always be recovered regardless of the mode of operation of the substation. In order to reduce the interface between the recuperator and substation, the recuperator’s connection to the substation has been modified. The new solution consists of connecting the recuperator between the substation’s DC busbar and general AC busbar downstream of the fiscal measurement equipment to allow reading of the energy returned to the grid. For this connection, a step-up transformer must be installed in series with the inverter to adjust the recuperator’s output voltage to that of the substation’s connection.

In the image, the schematic designed for the substations of Tres Cantos, Alcalá de Henares, Pinto, Leganés, Granollers and Castellbisbal and, if there are no new modifications, the one that will be adopted for future energy recovery installations in substations on the conventional network.