Safely through the Gotthard Tunnel

ALPTRANSIT GOTTHARD AG, as the principal, placed the order for the railway facilities in the Gotthard Base Tunnel with Transtec Gotthard as the prime contractor. Balfour Beatty Rail GmbH is a shareholder in Transtec Gotthard, and for its part appointed ABB to secure the 50 Hz tunnel infrastructure with gas-insulated medium voltage panels of type ZX0 and protection devices of type REF542 plus. The 16 kV switchgear and protection devices are predominantly installed in the tunnel system and function there under difficult climatic conditions with minimized maintenance.

With a length of 57 km, the Gotthard Base Tunnel will remain the world’s longest railway tunnel for decades. The futuristic flat trajectory line will be part of the New Railway Link through the Alps, leading to an improvement in rail transit times between Switzerland and Italy, and therefore between northern and southern Europe.

The new routing of the tunnel permits the use of qualified freight trains, which can be twice as heavy as today’s freight trains and reach a maximum speed of up to 160 km/h in the tunnel. Passenger trains will run through the tunnel at up to 250 km/h. These new dimensions in transit capability are achieved by a lower gradient and greater curve radii than in the existing mountain line.

The tunnel system consists of two parallel single-track tunnels, joined every 325 m by a 40 m long connecting gallery. Trains can change tunnels at two multifunction stations in the system, which also serve as emergency stops with evacuation facilities.

The connecting galleries, which also function as escape routes between the two tunnels, accommodate the electrical power supply systems for the tunnel infrastructure. As conditions in the tunnel are severe, gas-insulated ABB switchgear systems of type ZX0 from Ratingen are used. This switchgear, with a panel width of only 400 mm, is notable for its extremely compact design. With up to six panels grouped together in a fully functional switchgear block, it is possible to replace the complete unit in an extremely short time if a fault should occur. This functionality is of central importance to the operation of the Gotthard Base Tunnel: If it is necessary to enter a connecting gallery, rail traffic has to be stopped. As the prevailing ambient conditions in the galleries are aggressive, with salt ingress, brake dust, soot particles and abrasion from the rails and contact wires for example, the high voltage section of the switchgear is accommodated in the standard gas-tight welded enclosure and in addition the corresponding low voltage compartments have IP 65 protection, totally precluding the ingress of dust or water jets. The protection requirements are also related to strong pressure fluctuations in the galleries. As the trains pass the gallery entrances at up to 250 km/h, the pressure fluctuations in the area of the switchgear amount to ± 10 kPa. The ZX0 switchgear system with low voltage compartments was therefore subjected to a corresponding pressure test. For a period of 47 days, the system was exposed to 200,000 load cycles of rising and falling pressure for 10 s each. The passing of this endurance test demonstrated the optimum suitability of the switchgear for these unusual ambient conditions.

But that itself is not enough. The connecting galleries are also escape routes. Therefore, the requirements for internal arc classification and safety (see also page VIII) are significantly more stringent than, for example, in a transformer substation with restricted access. Although it is almost impossible for an arc fault to occur in gas-insulated switchgear, the safety of passengers must be ensured even in such an improbable event. The special pressure relief system in ZX0 ensures that the hot gases emerging in the case of an internal arc do not present any danger to persons in the gallery.

For optimum integration of the medium voltage switchgear in the protection system of the AlpTransit Gotthard project, ABB Switzerland is supplying the matching protection technology in the form of the REF542 plus unit. The protection units are installed in external control and protection cabinets and connected to the switchgear by special cables. The multifunctional protection and control unit REF542 plus has been on the market for over ten years, has proven its capability tens of thousands of times, and has been provided with innovative software adapted to meet the specific requirements in the tunnel. The units are spread along the entire length of the tunnel. They fulfil their fundamental task in the tunnel environment with the newly developed multi-stage distance protection: the nature and location of a fault are transmitted to the tunnel I&C system without delay, so that defective parts of the network can be systematically shut down.

The monumental AlpTransit Gotthard project is to go into operation in 2017. At present, 90 % of the excavation work for the Gotthard Base Tunnel has been completed. With the ZX0 medium voltage switchgear and the use of the enhanced REF542 plus protection unit, ABB is ensuring a maximum of quality and reliability for the safe and speedy transport of millions of passengers and tonnes of goods through the Gotthard Base Tunnel.

AT A GLANCE: Schematic diagram of the tunnel system with the two individual tunnels, the two emergency stops and the connecting galleries every 325 m.

Tunnel length:		57 km
Total length of all tunnels and shafts:		152 km
Excavated to date:		135 km
Start of construction:		1996
Commissioning (prospectively):		2017
Max. train speed:		250 km/h
Travelling time Zurich – Gotthard – Milan:	Present:	3 h 40 min
	Future:	2 h 40 min (further reductions conceivable)
Trains per day:		> 200
Freight traffic capacity:	Present:	20 million t/a
	Future:	approx. 50 million t/a
Peak altitude:		550 m above sea level*
Expected final cost:		SFR 9.67 billion

* At the same level as the city of Berne. For comparison, the peak altitude of the existing mountain line is 1150 m above sea level.