Under AC power supply, the electrical system of a modern electric locomotive has the following four basic elements:

1. the transformer (supplying a higher-frequency AC with a more manageable lower voltage and creating galvanic isolation),
   
2. the rectifier (a group of semi-conductors that turn the AC into DC),
   
3. the inverter (another group of semi-conductors to turn DC into a variable voltage, variable frequency [VVVF] AC, necessary to regulate output),
   
4. induction motors.

Of these, the part most resistant to size reduction is the transformer: for a defined input frequency and maximum power, its mass and size is pretty much a given. (For example, when Siemens developed a triple-voltage and slightly smaller cross-section variant of its standard 6.4 MW dual-voltage loco, it had to save mass and space on the transformer, reducing power to 6 MW.) Higher frequency means smaller mass. (For example, the first Thalys trains, which had transformers optimised for North France's 50 Hz system, had a limited top speed under 16.7 Hz in Germany.)

Swiss electronics giant is now trialling a new solution that reduces transformer size: ahead of the transformer, there is a second converter, one in which the high voltage is dealt with by switching the semiconductors in series. This converter supplies constant voltage constant frequency AC power, but of increased frequency, to a small medium-frequency transformer. ABB claims that this solution actually creates a better waveform (said differently, less harmonics that disturb other systems), significantly increasing converter efficiency.

The prototype under trial since February is built into a Swiss shunting locomotive, but ABB envisages its primary use as underfloor equipment in EMUs. I think it will be useful to further improve electric locos, too: the weight saved could be used to combine multi-voltage electronics and a last-mile diesel engine (not possible presently), or install a more powerful last-mile diesel engine (those in the first generation prototypes discussed in the diary range between 180-230 kW), or, in combination with permanent magnet electric motors, further boost maximum power (and thus acceleration at higher speeds).

_{*Lunatic*, n.
One whose delusions are out of fashion.}