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A medium-frequency transformer as used in the Pett demonstrator.
The locomotive operates under 15kV 16.7Hz electrification. The pilot installation was completed in mid-2011, and certification by the Swiss Federal Office for Transport (FOT) was achieved by the end of the year, enabling the locomotive to start shunting at Geneva Cornavin station in February. Pett has nine cascaded modules, eight for operations and the ninth for redundancy. The unit has 1.2MW nominal power and can supply 1.8MW peak for short durations. The dc output voltage is 1.5kV.
The overall weight is 4.5 tonnes, including cooling. Compared with traction transformers of the same power rating, Pett not only replaces the actual transformer but also the low-voltage rectifier. The main aim of the pilot is to study the feasibility of this technology.
Weight optimisation
Weight optimisation was an additional consideration. The power density (expressed in kVA/kg) of today’s transformer and rectifier combinations is in the range of 0.2-0.35. Future Pett generations under development will exceed this by a considerable margin, achieving values of 0.5-0.75. Further advantages include:
IRJ September 2012
improved energy efficiency from ac input to dc output from 88-90% to more than 95% compared with today’s average efficiency of a 15kV 16.7Hz standalone traction transformer which
is in the range of 90-92% reduced EMC and harmonics, and lower acoustic emissions.
All these factors make Pett ideal to
provide a small, lightweight but powerful converter that can be accommodated on the trains of tomorrow, and is suitable for operation in close proximity to passengers. As most large transformers tend to be stationary, traction is probably the application that stands to benefit most from reducing the transformer’s weight, and hence the area where this innovation must occur first. Although Pett is currently installed in a shunter, its real potential lies in multiple-units. Pett’s compact size means it can easily be fitted under the floor of the train or on the roof, maximising the space available for passengers while reducing the train’s power consumption. IRJ This article was written by Max Claessens, Drazen Dujic, Francisco Canales, Jürgen Steinke, Philippe Stefanutti, and Christian Vetterli from ABB.
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