Electric Train Power Supply Circuit

Discussion in 'General Electronics Chat' started by howartthou, Feb 2, 2010.

  1. howartthou

    Thread Starter Active Member

    Apr 18, 2009
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    Hi

    In Australia, as in most countries I expect, the power to electric trains comes from an overhead power line that feeds power through a spring loaded arm on the roof of the train.

    So thats one side of the current, in through the spring loaded arm, but where is the other side? :confused:

    If power on the arm is the positive side are the railway tracks the negative side? :confused:

    If so, does current travel back along the railway track to the power source in order to complete the circuit? :confused:

    Also, how does the circuit connect from the spring loaded arm to the railway track without electrifying the whole shell of the train which is made of metal? :confused:

    If not, where is the negative side of the circuit and how does it connect to the original power source to complete the ciruit? :confused:
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    I am not a train technician but I can say that the return path is the railway. The spring loaded arm can be isolated from the metallic locomotive (ie mounted on a palstic base) and connect it with a wire to the trains electric system. If the metallic locomotive frame is connected to the negative side of the supply which is also grounded there is no problem of electrification.
     
  3. howartthou

    Thread Starter Active Member

    Apr 18, 2009
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    Thanks Mik3, so do you uhink the current runs back down or up the railway track to the power supply?

    Is so it would have a long way to travel to get there I suppose...
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    It wouldn't have any further distance to travel through the rails than it would travel through the overhead lines.
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    I am not sure, but I believe the current provided to the train is AC and it is rectified (where they need DC) on the train. Therefore, if the current is AC, it oscillates back and forth in the track.
     
  6. Duane P Wetick

    Active Member

    Apr 23, 2009
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    See the French TGV rail speed record on U-tube (357 mph). They have a camera on the brush as the overhead sweeps back and forth.

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
    Last edited: Feb 3, 2010
  7. howartthou

    Thread Starter Active Member

    Apr 18, 2009
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    Thats quite amazing, its a wonder that train isn't airborne at that speed...

    Yeah, that makes sense that the current would go up and down to and from the power source if its A/C.

    What I am not clear about is that if the tracks are overloaded with electrons looking for a home wouldn't you get electrified if you lay accross the tracks making contact with both sides?

    Or is it like holding a live wire but somehow not being part of the circuit?
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
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    Both tracks would be at ground potential. Power from the overhead.
     
  9. howartthou

    Thread Starter Active Member

    Apr 18, 2009
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    Thanks Bill, I should know this but still not past the confused stage in my learnings.

    It makes sense that you need to contact the plus and minus side of the circuit to get electrocuted and since both tracks are the minus (ground) side and the overhead line the plus side, you would need to hang off the overhead line and touch the tracks at the same time, then you would be fried ;)
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Like a roman candle!

    But as long as you weren't grounded, no big deal. Check out this video........ http://www.youtube.com/watch?v=4SX6Ucbb1l8&feature=related
     
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