How is electric power transmitted to trains with the overhead cable?

Question

Since the overhead cable is only one contact, and any circuit needs to be closed, where does the current flow out of?

Answer 1

The circuit has the live power on the overhead cantilevers and is grounded by the rails which complete the circuit. This way there is no live power and ground right next to each other that humans or animals can be killed by.

Ironically, every locomotive is electrically powered. Most locomotives are diesel electric because a traditional transmission won't work. Basically the power is fed from a huge diesel motor into a huge generator. The power goes through a drive which controls the power. Then it goes to multiple traction motors simular to electric trains.

Correction: Every diesel locomotive is electrically powered, China still runs steam powered locomotives...

Answer 2

Both correct.

As for my 2 cents worth, the overhead power supply line is called the 'catenary' while the device that picks up the power on top of the locomotive is called the 'pantograph'.

Answer 3

the power goes thru the pantograph in to the traction motors ,it is used and it grounds out thru the rail curcuit. it is very little voltage .it the train were to derail then the wheels would become the route that eletricity would ground into the earth  and not the rail  instead ,then you can be eletrocuted if you touch the train and the ground at the same time

Answer 4

Everybody here is right, the power goes from the overhead catenary wires, thru the pantograph and the train, and out thru the rails and back to the power company.

This also means that, if there's a broken rail between the train and the power company, the power won't flow and the train will stop.  If there's a train derailment or accident that damages the rails, there will be a gap or the rails may not be grounded well, making the rail (compared to the surrounding earth) energized.  So, if you step on a rail that is broken or that is damaged, the power going thru the train will also try to go thru your BODY and will kill ya - 25000 volts (on the Amtrak Acela lines) is no picnic, so stay at least 3 feet away from the rails.  They are ALMOST always safe and well-connected, but why take a chance?

Answer 5

The circuit is completed by the track.

Answer 6

The current flows back through the rails and the ground.

(The 0V-potential is often called 'ground' because in many technical applications it is the ground, literally.)

A comment to Marc-Robertson: In the US most engines are diesel-electric, but in other countries (specially in Europe) there are also diesel-mechanic and diesel-hydraulic engines - see http://en.wikipedia.org/wiki/Diesel_loco...