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05.02.2009 
Siemens is to supply a new type of static frequency converter to power the metro rail
network in Nuremberg. Not only is the 60-megawatt plant smaller, quieter and more environmentally
compatible than the systems currently available on the market, but it also saves energy on
account of reduced power losses. The order for the new Sitras SFC plus static frequency
converter has come from E.ON Kraftwerke GmbH. The solution is to be installed onsite at
the Franken Power Plant in Gebersdorf, Nuremberg. It is the first order for a static
frequency converter of this new type.
Frequency converters for traction power supply are required to run trains, which operate
at a different power frequency that that of the conventional three-phase network. Instead
of operating at 50 Hertz — the frequency of the three-phase current supplied to normal
consumers — trains require single-phase power at only one-third of the frequency (16.7 Hertz).
A converter is therefore needed to reduce the frequency.
The order from E.ON comprises a turnkey container solution for two static frequency
converters — each with an output of 30 megawatts — including transformers, control and
instrumentation technology, and safety and control systems. The plant is scheduled to
go into operation in 2011.
The most innovative aspect of the Sitras SFC plus is the multilevel converter concept,
which features a modular system of semiconductor components and capacitors installed in
series — a feature that incrementally provides the required voltage in small steps.
Compared to the frequency converters for traction power supply currently on the market,
the new system operates with a greater number of voltage steps, which in turn means a reduction
in the switching rate of the individual modules. Given that each switching operation
results in losses in the semiconductors, the use of the multilevel converter concept
cuts the overall energy losses of the converter by around ten percent. Likewise, noise
emissions also fall, which means the system can be operated near residential areas.
Last but not least, the new system requires around 20 percent less space, because it
boasts a more compact design than conventional solutions. As a result, plant operators
save on land and building costs.
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