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What is the reason for employing lower frequency power for traction usage? LorenzoB 18:14, 12 September 2007 (UTC)
A bit beyond my technical knowledge, i'm afraid. Pickle 00:37, 13 September 2007 (UTC)
Depends on the distribution system, but much of it has to do with the characteristics of AC motors. On a DC distribution system, the AC to DC conversion was once commonly done using rotary converters, which run in synchronism with the AC input, and it was apparently less stressful on the machinery to have it running at 25 hertz than at 50 or 60 hertz. Once all of the substations go to solid-state equipment, though, this advantage is eliminated, and it's not uncommon to convert to local mains frequency and eliminate the separate traction network.
On AC distribution systems, the motors on the rolling stock might need a lower frequency in order to start effectively from a stop, depending on how they are built and connected. The lower frequency means less difference between a dead stop and synchronous speed, so again, potentially less stress on the equipment. My trusty Standard Handbook for Electrical Engineers fails me on the details, but does point out the common application (in 1941) of 25 hertz systems in the United States, and 15 and 16 2/3 hertz systems in Europe. --Morrand 22:25, 10 November 2007 (UTC)
And because wound traction motors can be built to run on low-frequency AC, giving the good characteristics of a series DC motor but allowing generation by alternators and transmission step-up and step-down by transformers. Electric motor #Universal motorsMeggar 01:26, 11 November 2007 (UTC)
Please take a photograph near Mehedeby in Sweden, where HVDC Fenno-Skan 2 crosses traction powerline Gävle-Tierp. This is the only crossing point of HVDC powerline and single-phase AC powerline in the world.