Technology & Breakthroughs

Siemens engaged in unique project

In order to ensure their traction power supply in the event of a partial system failure or unforeseeable network operating conditions, Swiss Federal Railways (SBB) has commissioned Siemens’ Smart Grid division to design and supply mobile 15-MVAr reactive-power compensation systems that can be deployed anywhere within the SBB rail network on demand.

The order was placed following a public invitation to bid. The project will result in the first mobile reactive-power compensation systems for a traction power supply in the world. Installed, for example, on rail cars, these systems can be quickly moved anywhere within the SBB traction power-supply network and deployed directly where needed. They will provide reactive-power compensation, improve voltage quality, and increase the stability of the network.

The order volume is 9.3 million Swiss francs ($9.8 million). The first two units, which will be located on the south side of the Simplon Tunnel, will be commissioned at the end of 2015. A third unit is earmarked for the network area Neuhausen am Rheinfall, Switzerland. Siemens and SBB also agreed on an option for delivery of an additional four mobile reactive-power compensators worth about 10 million Swiss francs.

The first mobile reactive-power compensation containers will be deployed on the south side of the Simplon Tunnel. This 20-km-long tunnel links Switzerland and Italy and is an international transit route for freight and passenger traffic. The compensators, which are installed in 40-foot-high cube containers, will stabilise the traction voltage in the network and improve power quality. The mobile containers are connected to the overhead contact line by cable via a plug-in connection. The containers can be connected to the network control system via a telecontrol interface. Auxiliary services can be powered with either 15 kV/16.7 Hz via the traction power supply or with 400 V/50 Hz via the national grid. Each container contains gas-insulated medium-voltage switchgear, power converter technology, a cooling unit as well as protection and control technology.

The Sitras SVC Plus (static var compensator) reactive-power compensation systems operate on the basis of voltage-sourced converter technology. Similar to the Siemens frequency converter Sitras SFC Plus, the core element of the reactive-power compensators is the modular multilevel direct converter technology. As a result, the voltage waveform generated by the system is virtually sinusoidal. The power converter consists of a large number of series-connected power transistor modules (IGBT) and capacitors – hence the name multilevel voltage-sourced converter. These series-connected modules act like a controllable voltage source that builds up the sine-wave voltage. This enables the low-frequency harmonic filters needed in existing solutions to be eliminated, which considerably reduces the space required for the entire system and allows it to be installed in containers.