The Swiss Electric-Steam Locomotives.

Updated: 7 Jan 2010
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A unique- and apparently lunatic- locomotive scheme was to generate steam by electric heating. This appears to make no sense; having gone to all the trouble and expense of electrifying a railway line, to use the power to run a steam engine with its less-than-impressive efficiency, rather than simple electric motors, seems demented.

It was not. There was (as usual) a good reason.

Left: One of the Swiss electric-steam tank engines.

The Swiss Federal Railways had a highly electrified system during the Second World War, but retained little 0-6-0 tank engines for shunting. Due to war conditions coal was in short supply, but hydro-electricity remained plentiful. Therefore some of these small steam locomotives were converted to raise steam by electric heating. Power was taken at 15 kV, 16.6 Hz from overhead lines by a pantograph, and fed to resistance heating elements in the boiler, via two transformers rated together at 480 kW. Water feed was by normal steam injectors. These unique locomotives also retained the capability of being fired by coal in the usual way.

Left: Another view of the electric-steam tank engine.

Left: And another view. The chimney seems to have been extended in this photo.

When I first published this page I found it strange that power was distributed at such a low frequency; one obvious objection to 16.6 Hz distribution is that all the transformers would be three times the size of those for a conventional 50 Hz system. The answer is that due to the state of electric motor technology at the time, electric locomotives used serial wound commutator motors as traction motors. They were essentially DC motors running on AC. Without using electronics, it is difficult to control the speed of an AC induction motor. As Fehér Tamás, one of my correspondents, put it: "About 18Hz is the highest frequency where sturdy-built DC electric motors can be run safely with minor modifications. There will be occasional sparks and arcs at the commutators, but it is tolerable. Go over 20 Hz and you will have frequent circular-fire shorts on the current feed brushes, quickly destroying the motor."

I would like to thank all those who wrote in to point this out to me, and I can only offer my apologies for taking so long to update this page.

Left: This is engine E 3/3 pictured in 1942.

Left: This was clearly taken at the same time as the picture above.

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