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Two competent partners - one solution: electrical enclosure manufacturer and thermal management specialist develop a concept that withstands the alternating pressure load in tunnels 

 

The Gotthard Base Tunnel impresses with many outstanding figures:
It is the longest railway tunnel in the world at 57 km and its tunnel run, with all the transverse and connection tunnels, stretches over 154 km. From 2016, passenger trains should have a top speed of 250 km/h, reducing the traveling time e.g. between Milan and Zurich to under 3 hours and should almost double the haulage capacity on the Swiss North-South Axis to 40 m tons of goods.

Looking at these figures, it becomes clear that the safe and smooth operation in the tunnel must be guaranteed at all times. In order to achieve this level of safety, the technology used in the tunnel must always be up to date; this applies not only to the whole system, but also to the individual components. The most important components here are Pfannenberg's electrical enclosure climate control units, which are situated, in the 176 cross passages amongst other places.

Pfannenberg and Swibox - a time-tested team

Two long-term partners have joined forces once more for the Gotthard Base Tunnel project: Pfannenberg, a medium- sized company with its headquarters in Hamburg and specialist for the thermal management and process cooling of electrical enclosures, and the company Swibox, also an expert in the area of customized electrical enclosure manufacture with its headquarters in Balterswil in Switzerland.

At the beginning of the cooperation, standard products from Pfannenberg's comprehensive portfolio of products were installed in the Swibox switch cabinets. The first time the two companies developed a climate control concept for a specific customer was 2003, during the "Lötschberg Tunnel" project. This concept was designed especially for the challenging demands of railway tunnel applications. 

Electrical enclosures withstand every alternating pressure

The largest technical challenges were the high requirements to the system of protection of the electrical enclosure, IP65, and also the high alternating pressure load which is caused by the trains passing through.

When entering the tunnel, the train pushes the air ahead of it, causing overpressure until the train passes by the cross passage where the electrical enclosures are standing.

As soon as the train has passed, the overpressure transforms suddenly to a corresponding under-pressure

Fig : 1 cross passage Lötschberg Tunnel with electrical enclosures and climate control units

All the electrical enclosures and the installed cooling units are exposed to the load of this alternating pressure of up to +/- 5 kPa. It had to be ensured that all devices can withstand this alternating pressure mechanically, simultaneously implementing the high system of protection.

It was possible to meet these requirements, thanks to the mechanical unit construction (Figure 3: Swibox electrical enclosure with Pfannenberg DTGT cooling units without top cover) developed especially in cooperation with the company Swibox. This construction ensures a leak-proof separation of the surrounding (outer wall of the unit) and the inside of the electrical enclosure (unit inside), also under pressure load. A special feature here is the developed pressure body inside which the components of the inner cooling circuit are housed. Therefore, it was not enough to use reinforced sheet metal: the selection of a suitable material and the increased material thickness in combination with specially installed stiffening plates led to the desired compressive strength.

Climate control concept of electrical enclosures does not only mean cooling

Another challenge in tunnels is the ambient air. Large temperature differences ranging from -20 °C to +40 °C, maximum humidity of 100%, and ferrous abrasion of brakes, rails and contact lines in the ambient air increase the risk of corrosion and show how different a tunnel application is compared to standard applications.

Therefore, a special climate control concept had to be established for specifically this application. It becomes clear that it is not just about the cooling of the components when you look closely at the task of thermal management and process cooling of electrical enclosures again. It comprises an extensive protection for the electronic components against damaging ambient influences such as dust, moisture and temperature.

Naturally, protection plays a special role, but also other factors can be influenced by thermal management and process cooling such as the length of service life of the electronic components for example. Many developers and design engineers are aware of the fact that climate control of electrical enclosures is necessary, but often not where the actual requirement comes from. Here it is helpful when one looks at the technical data of frequently installed components closely, especially cost intensive components like controllers. The technical data includes information on minimum/maximum operating temperature, humidity, and condensate but also on other critical parameters like the dust pollution.

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