Electronic – Does some current return to the power company through ground

Your question contains one very common misconception, and that is that large amounts of current flowing through ground is normal.

In this diagram, notice the lack of a particular path for current flow into or out of ground. As long as everything remains balanced and a power line isn't touching the earth or a tree, there is no path for current to travel through ground (except some minor leakages).

Here is a wye connected four wire system. Notice how the ground is connected directly to the neutral point in the center, and the neutral (N) line has no coil. In this system, the neutral line is the return path for all single phase loads - that is, anything that is connected from a phase to the neutral. Phase to phase connections are still available, of course. But current flow through ground is still not normal.

Which is a great thing - if you put a current transformer on the ground connection, you now have a high reliability mechanism to detect if the system is grounded. This is a standard feature on the power grid.

Now, lets say a high voltage power line has been broken and is laying on the ground. At 500 KV, there is definitely going to be some current flow through the earth. And as with all current flow, voltage drops when current flows across a resistance. Starting from the 500 KV at the end of the line, and reaching zero back at the nearest system ground connection, means that there can be a huge difference between one foot and the other in that vicinity. In the industry, we call this step voltage differential, and it can be lethal. It's the reason why you may have heard that you need to shuffle away from lightning strikes and power lines, rather than walk; that keeps your feet close to each other and prevents a current flow from leg to leg.

On the off chance that a line has been downed and grounded, the current flow will radiate away from the point of earth contact to whatever path is most favorable for current flow. If the topsoil is recently wet, it will tend to stay there. If everything around is fairly dry, there may not actually be much current flow at all, and it will radiate in nearly every direction as the voltage charges the ground. It will flow through ground water, if it can get there.

As far as the difference between AC and DC grounding events, the physical characteristics of DC make it more likely that it does not find a good path back to the nearest system ground, which makes it more likely to have a potentially lethal step voltage differential.

I've been reading about this phenomenon after reading your question and the paper you posted . I can't see how that much current could be travelling through ground unless a similar percentage of Minnesota either uses SWER or is wired incorrectly. If that's not the case then the statement must be false.

Claims of current travelling through plumbing is a problem with incorrect wiring for sure. If there is a solid connection from the neutral at the service, to the transformer in the street, to the transformer in substation and back to the plant then it must be lower than 59%. However there is a parallel path through ground rods connected to transformers throughout the grid and at services. I can't see it accounting for such a large percentage of current though.

I measured the resistance between 15 and 25 KOhms through 1 foot of damp soil with my multimeter. (Curiously it was rising steadily like I had my meter on a capacitor and then would drop and restart at different values with no particular pattern). Compared to the resistance of utility wires it is obviously very high.

I have seen (I'm an electrician) a single phase 100a service lose the neutral in the meter socket. The customer called because the screws connecting sections of the baseboard heater (hot water) were glowing red. All of the power being used in the house was travelling through any path to ground it could find.