Underground river of lightning? This question has been asked before but not the same way. A generator uses a magnet to push electrons down a wire to my house and turn on my light. Then those electrons take the expressway back to the plant to complete the circuit. I get the idea. What baffles me is that what happens when a tree hits the power pole and the electrons take the short ride to the ground? Does the power plant just lose those electrons? Does it make new electrons? I know that when people wire the main neutral to the copper plumbing in their house, their appliances still run. Every single electron that has ever entered their house has left through the dirt. Are they still there piling up? Or are they Travailing through the ground back to the power plant like an underground river of lightning? Is it dangerous then to go into a basement near a power plant? I jest but the question is real.      
 A: Electric current travels in a loop: it goes from one pole of the generator, through the circuit, and back to the other pole of the generator. As a result, the electrons never "pile up" anywhere. If a powerline falls to the ground, electrons then travel from that point back to the generator, instead of taking the longer trip through your house.
Electrons are everywhere: in the generator, in the wiring, in the ground, etc. So the electrons that "leave" the generator are not the same as the ones that travel through your house. What happens is that the electrons at the poles of the generator move slightly. Their movement in turn pushes electrons in the wiring, which push some electrons further along along the wire, etc. 
So far I've talked about electrons "travelling", but that is a grandiose word for what they are doing. In the entire circuit, all the electrons move very slowly. Inside a wire, their speed is of the order of millimetres per hour. Outside the wire, in the ground, their speed will be even less, as there are far more electrons available, and less movement by more electrons produces the same current.
This whole situation is made more complex by the fact that the generator does not produce a DC voltage, but AC. As a result, the electrons in the wiring will be pushed one way for a 100th of a second. In that time they travel far less than a micron. In the next 100th of a second they travel back, and they keep doing that 50 times per second (50 Hz). Hence, with AC, the electrons from the generator will never even get outside the generator housing, no matter how long you wait.
