Three-Phase AC Traction

In the history of german diesel locomotives there are a number of oddities and things that seem reasonable, but were just never built in mass. The west-german six-axle diesel locomotive is one example — for every major diesel locomotive generation, someone built a prototype of a heavy six-axle diesel, but DB never bought any. Another one would be the three-phase AC traction phase.

Most diesel locomotives have their motor turn a generator which produces electricity, and are then more or less identical to an electric locomotive past the transformer. The other way (besides normal mechanical transmissions, which can’t transmit as much power but have proven popular for DMUs) is with a hydraulic converter in between, a method that is somewhat less efficient but weighs less. German diesel locomotives are usually diesel-hydraulics, although the GDR imported a lot of diesel-electrics from the soviet union.

In the time when three-phase AC traction got popular, though, it seemed that this new and more efficient technology would displace diesel-hydraulics in Germany, with most diesel locomotive producers switching to this system. During that time, HGK seems to have bought millions of diesel-electric road switchers from MaK, such as DE85 (NVR number 98 80 0272 023-9 D-HGK) here, passing through Cologne West station.

The funny thing is that it somehow just… ended. DB never bought any three-phase AC diesels (in fact, it is a long time since they bought any new diesel locomotive at all), MaK went back to diesel-hydraulic only, many other locomotive builders folded or were bought, and the main new player, Voith, literally invented diesel-hydraulic technology and will probably not touch electric transmission with a ten-foot stick. The technology has easily prevailed in electrics and hence the modern and quite successful diesels which are based on electrics (Siemens ER20 and Bombardier TRAXX DE) are diesel-electric with three-phase AC as well, but the huge road switcher and switcher markets are almost completely hydraulic right now.

Things are looking interesting for the future. DB has recently ordered a huge batch of diesel-hydraulic road switchers from Voith (which should start delivery soon), but they also tendered a request for new road locomotives, without specifying the desired technology, so anything goes there. At the same time, Schalker Eisenhütte, recently decided to get into the mainline locomotive market — with a diesel-electric AC road switcher.