Unlike AC return currents that generally follow a path that matches the transmission line,
DC currents can flow through the entire earth. In essence, the electrodes are completely decoupled.
That does mean they’re susceptible to some environmental issues though. They create
magnetic fields that can affect compass readings and magneto-sensitive fish like
salmon and eels. In ocean electrodes, the current can cause electrolysis,
breaking down seawater into toxic chemicals like chloroform and bromoform. And, stray
electrical currents in the ground can flow into pipelines and other buried structures,
causing them to corrode. This is also a problem with some electric trains that use
the rail as a return path.
You may have heard that electricity takes the path of least resistance,
but that’s not really true. Electricity takes all the paths it can in accordance with their
relative conductivity. So, even though a big steel rail is a lot more conductive than the earth,
return current from traction motors can and does flow into ground, sometimes corroding adjacent
pipelines, and occasionally interfering with buried telecommunication lines too.
@imhotep
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