Fresh Air for the Gotthard Base Tunnel: Successful completion of the commissioning of the world's most powerful ventilation system

There is no hesitation in using superlatives about the Gotthard base tunnel. «With the fans having an outer diameter of approximately 3.5 m, it is not only the largest but also the most powerful tunnel ventilation system in the world. It has an installed maximum power of 15.6 MW – about as much as 25 Formula 1 racing cars together», says Alwin Larcher, who holds the position of project director for ABB in the Lot C of AlpTransit Gotthard AG (ATG). In 2011 ABB had received the job order for the operating ventilation together with the German TLT-Turbo GmbH. ABB was responsible for the entire electrical equipment of the system, while TLT was responsible as consortium manager for the installation of the giant fans and the associated valves.

Over the years, this major project required intensive efforts for the planning, engineering and installation stages. Early in 2015, ABB and TLT approached the final challenge: the commissioning (IBS). «In the base tunnel, with its gigantic dimensions and the complex interaction of various systems, it was anything but a routine work», stressed Larcher.

This begins already with the medical tests by the Swiss Accident Insurance Institute (SUVA) with respect to the fitness of the employees to work in the tunnel and the required safety trainings by the tunnel operator in order to be allowed to work in the longest as well as the deepest rail tunnel in the world in the first place. In some places, 2,300 metres of rock cover the tunnels, the surrounding rock temperature of which is up to 46° C. The two ventilation centres are located in the shaft head cavern in Sedrun, about 800 metres into the mountain and 800 metres above the road, and in Faido in a portal building next to the 2.8 km long access tunnel to the west tunnel. The multifunction stations, which also include the emergency stations, can be reached only through the northern and southern portals in Erstfeld and Bodio as well as by car via the access adits in Faido. They are around 20 km and 17 km from the north and south portal respectively. The driveways are accordingly long.

«The commissioning was truly outstanding,» Larcher looks back at the most recent past. The commissioning included not only the electrical components for the fans in the ventilation centres but also the integration of their control in the master control system of the tunnel and, for example, also the testing of the tunnel sensor system, which includes more than 80 sensors for temperature, humidity and air velocity in the two tunnels distributed over the entire length of the base tunnel. Also the integration of a fire location detection system in the four emergency stations was masterminded by ABB.

The meticulous documentation of the testing method for the installed ABB components have contributed much to the successful commissioning. «The value of an exact, well-structured description of what was exactly installed where, cannot be overestimated in such a large project with numerous parties involved», emphasizes Larcher.

The components and systems were thoroughly tested, in individual tests as well as in combined tests for ventilation scenarios (scenario manager) or with various key aspects, for example, the volume of air delivery or the event control. It is also exciting that the control of some external systems is triggered via the computer of ABB ventilation, for example, the automatic doors of the emergency exits in the emergency stations.

«The interplay of all the systems in the base tunnel, from the train protection to the sewage system, the lighting and our ventilation as well as a dozen other systems, is crucial for the functioning of this structure of the century anyway», stresses Larcher. The total integration has been addressed in August. From October, the other integral tests of the entire system and all systems involved are performed by the AlpTransit Gotthard AG. Here, test runs with train compositions are also undertaken.

Praise for the successful commissioning also came from AlpTransit Gotthard AG. «After the successful completion of a major part of the tests, which have been carried out since early 2015, I would like to thank all parties involved for their tireless efforts and flexibility», says Andreas Huber, senior construction manager of operating ventilation / lifting devices at ATG.

«This is overall a nice success story for ABB. And as a Swiss, one is naturally proud to have contributed to this project of the century», opines Larcher, who has seen complex large projects through in Australia and in the Middle East. And for his colleague Ralf Rösch, lead engineer, responsible for the control system, and employed at ABB since 1994 in the tunnel industry, it was even a matter of the heart: «As an old tunnel builder, I have put my heart and soul into the project and left my position as head of department temporarily to rest in order to totally burrow into the job», he says with a smile. When it comes to burrowing into the job, one takes the word for it for both of them. The entire project team put heart and soul into the project, because the ABB team involved as well as that of the TLT-Turbo GmbH have remained relatively constant over the years, say both of them and underline the trustful and cooperative collaboration within the consortium.

There was a lot to do, since ABB and TLT tied an extensive overall package for this job order – from the 24 jet fans at the two tunnel portals in Erstfeld and Bodio up to the eight major supply and exhaust fans in the ventilation centres in Sedrun and Faido, as well as the installations in the multifunction stations in the tunnel tubes. The two ventilation centres form, so to speak, the «Lungs» of the entire system and are responsible for the exchange of air inside the tunnel. The supply air fans supply fresh air from the outside – in Sedrun via a 800 m long vertical shaft – that is regulated by shutters and is then distributed in the tunnel. The exhaust air is transported outwards through an own shaft via axial fans with up to 300 km/h (air speed in the fan).

The whole system is designed as redundant for safety reasons. Because in addition to the regular exchange of air, the fans must primarily ensure enough fresh air in the emergency stations in the event of a fire and simultaneously suck the smoke over long exhaust shafts specifically, so that the travellers can get off the train in an emergency and can get to safety. «The <brain> of the ventilation system – and thus the entire programming – is very important here for the precise adjustment of the fans and the shutters in various scenarios», says Rösch. This master control system regulates approximately 50 such possible cases – from normal and maintenance mode up to the event of an explosion.

«The systems have functioned best during commissioning. However, we had to conduct our tests usually at night for security reasons and because of the very high air velocity of the aspirated air», says Larcher. Would the logistics and planning have been the major challenges at all in this project, it would be due to coordination of the own works with numerous other suppliers underground. «In spite of meticulous planning in the office, we had to look for fast solutions on site several times. Sometimes it looked totally different than expected, for example on the construction site», he recalls. The mere delivery by railway carriages and the installation of the fans with a propeller diameter of 2.8 m in the narrow ventilation centres have been a challenge.

This fall, the first trains will run in test mode in part with up to 275 km/h through the Gotthard base tunnel. In mid 2016, the north-south connection will be officially opened – with ABB as the main partner of the festivities named «Gottardo 2016».