Tight cabinets and sockets for the new Gotthard railway tunnel

The high suction and pressure loads in railway tunnels are a major challenge for electrical installation

Gigantic construction project

In only a few months the new railway tunnel through the St. Gotthard Massif will open and cast a shadow over all structures previously built in Europe. Believe it or not, it was driven 57 km through the mountain massif in the Swiss Alps (Fig. 1). It is the world’s longest railway tunnel and its tunnel section with all crossing and connecting tunnels stretch a total of around 154 km. Test trains are current operated in both tunnel tubes at speeds of up to 275 km/h. Then the trains should use the new tunnel at speeds of up to 250 km/h, starting on 1 June 2016 – earlier than originally planned. Therefore, travel time between Milan and Zurich is reduced to less than 3 hours and transport on the Swiss north-south axis can be nearly doubled with 40 million tons of goods. With a cost of CHF 12 billion, it is the largest construction project of a new north-south connection for high-speed trains through the Alps.

Refined safety concept in the planning

With these dimension, nothing was left to chance. Safety was the highest priority. The concept of the new Gotthard base tunnel has two tubes arranged around 40 m apart and connected by crossways around every 325 m. With two double lane changes,

entire trains can switch from one tube to the other, which is applicable for maintenance work or in emergency situations. These track changing points are situated in two so-called multifunction points, which also accommodate parts of the ventilation installations and emergency stop points. They are designed for an emergency stop of a train and are provided as escape and evacuation points for travellers who can be removed from the tunnel with an evacuation train. It is not necessary to cross tracks by means of stairs or lifts on the rescue route to the other tunnel tube. The emergency stop points and their side and connecting tunnels are supplied with fresh air in the event of an emergency. While smoke is extracted from the emergency tube, a low pressure in the emergency stop point is sufficient to keep the escape route clear of smoke. The crossways serve as an escape route apart from the emergency stop points.

High safety standards for products

Similar in scale to the gigantic construction project and its safety concept are the requirements on the products that are used, which far exceed the previously known extent. Deutsche Bahn defined the special safety status inspections for the existing and planned railway tunnel in Germany, which relate to all technical details of the system and the effects to be expected. Especially influential factors are suction and pressure, which act on all components installed in the tunnel. The defined requirements are based on whether the components can survive aerodynamic forces of suction and pressure stresses, remain in their position and continue to function. Equally important is the question of whether the product actually remains tight in light of the high forces or whether the enclosure cover lifts enough for penetration of dust particles and moisture and can result in impairments of the system parts. Ultimately every failure and all maintenance would cause a standstill of operation in a tube, which would result painful delays in operation with respect to the use of the line as expected and thus result in lost profits. The client, “AlpTransit Gotthard AG” has defined stricter standards and established the highest requirements on the service live of all products that are use. Even the tunnel does not assume these extreme dimensions in Germany, similar relationships apply and are already taken into consideration in the planning. There is no standard or directive for these extremes, therefore a requirement catalogue was developed from the findings in prior tunnel projects, which should be used for all tunnel projects. 

Challenge for electrical installation

The components for electrical installation are primarily located in 176 crossways (Fig. 2) between the two tubes. The boundary conditions could hardly be more difficult, because the entry of a train into the tub at a speed in excess of 160 km/h compresses the air and the air pressure increases accordingly. Although the airflow of the train from the cross passages are largely prevented, the pressure or negative pressure of the air compression penetrates nevertheless into the cross passage and applies a stress of up to +/- 1 t/m² on the surfaces of the installed hollow elements. It must also be ensured that all equipment can mechanically withstand this pressure change and the high protection rating IP 67 (dust and waterproof) remain intact. Like the Lötschberg base tunnel already commissioned in 2007, two long-term partners participated in the Gotthard base tunnel. Switch cabinet specialist Swibox AG of Balterswil (Switzerland) provided the cabinet concept and the management of the project, and Pfannenberg GmbH of Hamburg, specialised in the cooling systems, handled the construction of the cabinet climate control required for construction. Swibox AG developed a completely new cabinet system with a sealed cable interface in the cabinet base for the Lötschberg base tunnel in 2003, which was designed for a pressure load of +/- 5 kPa or 500 kg/ m². Since the Gotthard base tunnel increased the requirements to +/-10 kPa or 1 t/m², the complete system must be fully revised and tested. The solution is based on clever interior cabinet supports for which a patent application was filed. 2880 of these cabinets have been developed by Swibox for the Gotthard tunnel and installed in the crossways. 

Air-conditioned cabinets

However, there remained the additional challenge in tunnels of environmental air. Large temperature differences of -20°C to +40°C, maximum air humidity of 100%, ferrous debris from the brakes and rails and copper from the catenary in the environmental air increase the risk of corrosion considerably. A special climate control concept was needed. This was the task of the Pfannenberg company. In this case, the state of the art was surpassed once more with the development of an entirely new concept specifically for the Gotthard tunnel. It underwent extensive testing as a complete system together with the switch cabinet from Swibox in a testing laboratory developed for such projects and successfully competed 200,000 pressure changes of +/- 10 kPa. The overall testing procedure was conducted by a neutral inspection authority and monitored by the Swiss Accreditation Service for standards (SAS). In addition to the cooling units form Pfannenberg, which are now used primarily in the mountain interior (environmental temperatures of up to + 40°C), heaters were also needed in the portal areas (environmental temperatures as low as -20°C). These heaters ensure that the temperature in the switch cabinet does not drop below the dewpoint. The dewpoint is the temperature of humid air that must be undercut with a change in pressure so that the water in the air is separated as condensate. The relative air humidity at the dewpoint is 100%, which means the air is fully saturated with water vapour. 

Sealed junction boxes

The components installed in the travel tubes (Fig. 3) are exposed to even greater soiling and aerodynamic influences. For example, the escape route lighting is installed here must be fused individually to ensure that only one luminaire fails when damaged and the power supply to the remaining luminaires remains intact. With a tunnel length of 57 km, there is a great deal of cable, junction boxes and automatic control units, so the possibility of rapid, safe installation was a key factor in the choice of supplier. The choice ultimately came down to Rapid-Box (Fig. 4) from German enclosure specialist Spelsberg. The enclosure system was developed specially for safely installing uncut conductors of up to 50 mm² (Cu). The safe junction takes place with a 2.5 mm² conductor or via CEE socket (3-pin or 5-pin) in the enclosure cover. Fuses and sockets are supplied pre-wired. Installation at the junction takes place without the need to separate the main or supply line (Fig. 5). This technology enables flexible installation that is capable of extension even after commissioning. The main terminal can also be used as a connecting terminal for two cut conductors. With the use of CEE sockets, equipment such as luminaires can be connected and maintained quickly and efficiently. Installation takes no more than 15 minutes, so the system drastically reduces work. This quick installation is also a key advantage in regard to maintenance times, which have an immediate effect on the availability of the system. Therefore, assembly time and costs, as well as cyclical maintenance costs - e.g. for replacement or extension of junction boxes - are reduced. In addition to tunnel systems, other structures with long stretches of cable, such as industrial halls or high-rise buildings are ideal applications for the new system. The Rapid-Box has a modular design in order to offer the right solution for every feasible application. There are two basic versions: The standard variant in accordance with EN 61439-2 (VDE) and the variants for fire protection installation with functional integrity in E30, E60 or E90 in accordance with DIN 4102 and EN 1363, which is also used in the Gotthard tunnel. Individual components of the Rapid-Box can be combined individually according to the concrete task. For example, sockets in the cover or cable screw couplings on the enclosure are available. There is a possibility of external earthing and various automatic circuit breakers. All switching device combinations are VDE and MPA-certified. You can also choose which terminals are used. The maintenance-free, raised terminal block can be variably fitted for 1 to 5-pins. The spring-mounted sheathed nut for feed-through wiring assures fault-free operation even when exposed to heavy vibrations. The junction itself takes place via a spring-type terminal. Various cross-sections and rated currents can be accommodated here, so the interior of the Rapid-Box can be assembled precisely to suit the task. The variable equipment of the cover factors in customer wishes. Seven different seal sizes, including bush, are available depending on the conductor diameter. The enclosure is extremely durable and UV-resistant and can withstand extreme stress from weather conditions or dirt, so installation in corrosion-prone areas like the Gotthard tunnel is also possible. The low-smoke properties of the material also assure minimal release of harmful substances and smoke development in the event of a fire. The new Rapid-Box can be installed on ceilings, walls and cable trays. The attachment points are arranged on the outside of the enclosure, so the Rapid-Box can be installed without the need to open it. Covers and screws are also captive, so installation by hand is especially easy – a major advantage when working on a ladder or above your head. The Rapid-Box was certified throughout Europe: The switch device combination conforms to EN 61439, the fire resistance testing in EN 1363 compliant. In order to fulfil the extremely high safety standards of AlpTransit Gotthard AG, the Rapid-Box underwent additional testing before installation. It was especially important that the protection rating is also retained in consideration of high pressure and suction loads. A practical laboratory test provided certainty: Even after 200,000 cycles in which the Rapid-Box was subjected to a pressure of +/-10 kPa, the enclosure and its silicone seal remained stable and no pressure loss was detected even after 30 minutes. Therefore, the strict requirements of the Swiss tunnel builders were fulfilled and the Rapid-Box could be used. The described system of junction boxes is universal and highly versatile in use, not only in the lighting of escape and rescue routes, as mentioned in the example, but also in distribution systems for mobile devices with the use of standardised plug connections for maintenance tasks or for rescue forces. 

Resume

The safety requirements for construction and operation of railway tunnels are especially strict. In the new Gotthard base tunnel, with the world’s longest tunnel at over 57 km, requirements were increased further. Since trains will pass through the tunnel at speeds of 250 km/h, all installed components are subjected to enormous draught and suction forces. There are also dramatic temperature differences, high air humidity and extreme dust loads. Special solutions assure reliable functional integrity and protection of all components: Climate control systems from Pfannenberg in high-density switch cabinets from Swibox and junction boxes from Spelsberg satisfy demanding tests and guarantee safe operation under extreme conditions with retention of highly variable flexibility.

Summary

Tight cabinets and sockets for the new Gotthard railway tunnel

The environmental conditions that are prevalent in the tunnel are different than the conditions outside. These special conditions have not been regulated by standards. In order to safely ensure operation and offer a high security level, it is necessary to recognise and take these extreme conditions into account. The article describes these extreme influences on electrical systems and the example of the Gotthard tunnel project and illustrates experience gathered thus far.