Frequency dictates the size of a transformer’s iron core, which in turn influences the radius of the copper windings and therefore the amount of copper used.
As frequency increases, it’s possible to reduce the core size. ABB has used insulated gate bipolar transistor (IGBT) power semiconductors to increase the frequency to several thousand Hertz before using a compact medium frequency transformer.
While this sounds like a simple approach, ABB had to overcome significant technical challenges to develop the PETT because many aspects differ from conventional low frequency technology, including using alternative materials for the core and windings, as conventional materials would have led to greater losses at the higher frequency.
ABB also had to develop a solution around the limitations of existing semiconductor technology and so the PETT features a series cascade of converter modules so that the unit can be scaled to the required duty.
The PETT delivers significant weight and size savings as well as much improved power density and reduced noise levels.
On trial in Switzerland
As part of ABB’s long-term partnership with SBB (the Swiss Federal Railway), a pilot PETT installation is currently under trial
on a shunting locomotive for use on the
15 kV AC and 1.5 kV DC (direct current) lines at Geneva main railway station. In service since February 2012 and weighing in at a total of 4,500 kg, the pilot PETT has 1.2 MW nominal power and can supply 1.8 MW peak for short durations.
Despite its current service, the PETT’s real potential lies in powering multiple unit commuter and high speed trains.
“The innovative use of power semiconductors in a core component such as traction transformers opens up new opportunities for rail markets around the world, and should be extendable across a range of other applications,” said Markus Heimbach, head of ABB Power Products’ Transformers business.