Sunday, May 27, 2012

Trains! Trains Everywhere!

     Though I am a biomedical engineer and view the biomedical technology field as the most interesting to me, that title cannot stop my continuing fascination with trains.  Trains are essentially one of my now-not-so-secret childish fascinations.  Madrid has a model train museum just south of Atocha, off the Delicias metro stop, so if anyone wants to join me there this Saturday afternoon, admission is free!
     Speaking of trains, Madrid has a gigantic subway system and a substantially developed light-rail network.  Both of these commuter train systems are also complimented by the Spanish passenger train system that has a large presence in the Principe Pio metro station and even continues out past Segovia, where we visited on Saturday.  I also spotted some tracks whilst on the lookout from the Alcazar castle.  My real technological interest with these trains though, is in how they are powered.
     One of the first details that I noticed about the metro lines in Madrid was the single suspended bar that carries the electricity needed to power the trains.  Obviously the metro trains are electric powered, as it would not be very practical to have huge quantities of exhaust pumped out from a diesel engine into a confined tunnel, but what I found curious was the fact that it was only a single bar that carried the power. My first familiarization with electric powered trains was with the light rail system in San Diego, California.  These trains, also electric powered, run while connected to not one, but two powered lines suspended above the tracks.  Even with my limited engineering knowledge as a young child, it was not hard to figure out that the electricity came from one wire, went to the train, and then through to the other wire, thus making a complete circuit.  Later I would come to understand that having two wires meant that the whole train ran in series with the power supply, but such a case is completely nonexistent here in Madrid!  I saw the single power rail and instantly wondered how the train worked without having both rails.  
     After some speculation that occurred in the Nuevos Ministerios metro station with Steven, Evan, Allen, and myself, we came to the conclusion that the trains run as closed circuits in parallel with the powered rail.  At this realization, everything about the metro's power situation was made perfectly clear!  The powered rail contained an extremely high voltage at its source and thus provided a large DC current for the purpose of powering the train.  One hydraulically driven power connector arm on the first car and one hydraulically driven power connector arm on the last car provide the two connections necessary to run the trains in parallel with the source voltage.  Additionally, the fact that Madrid's metro runs on a suspended rail instead of the three rail system of New York and London means that the Madrid metro can run at even higher voltages of most other subway systems, allowing for greater efficiency in power transmission due to less loss of voltage due to the natural resistance of the power rail itself.  Furthermore, the fact that the trains are all in parallel with the rail means that they operate at the same voltage as the rail itself, with current being split between the rail and the trains.  Such a setup is advantageous for two reasons, the first being the fact that the voltage through the train is held constant at all times, preventing damage to the train, and the second being the fact that the trains will only have enough current pass through them at any time to power the train and all excess will remain flowing through the rail, allowing for greater efficiency in transmitting the power through one rail to all the other trains on the circuit.  For safety, the other two metal rails provide a ground for the trains themselves, as the steel wheels are in constant contact with the steel rails and the static charge buildup on any one particular car is instantly dissipated into the ground rails.
   Thus, my childhood curiosity has been satisfied.  I'll admit that I think of this group discovery most times that I see the suspended third rail, so feel free to call me out on it.  The offer to go to the train museum with me this Saturday is still on the table!  The website is available here.  Thanks for reading, and have a nice day.

1 comment:

  1. Sorry for all the edits, I had trouble with the title not having a line break.