I'm a 1st year EE student and i'm trying to get my head around earthing systems at the moment and could do with some help.
The first thing that i'm struggling to understand is how current establishes itself through the earth in the case of a Single Wire Ground Return system.
In the schematic above, i understand that the high potential top wire will allow electrons to be 'shuffled' back and to toward a place of lower potential, i.e. ground. I'm having a hard time explaining however, how a force exists between the ground below the load on the right, and the ground connected to the transformer winding. In a conductor within a copper wire for example i understand how the electrons are 'pushed' and 'pulled' in a specific direction, but how do the two grounded points 'know' that the other exists, and therefore that there is a complete circuit, without a wire?
My next question is most likely answerable from the first, but in an AC system, why is it the case that current requires a return path to the transformer as opposed to simply ending with the ground after the load?
Thanks for any help - sorry if the diagram is not so realistic!