This is a follow-on question to an earlier question of mine; I think it deserves its own question, though.
I am trying to learn as much as I can about how current in a power grid (transmission and distribution) returns to the substations, power plants etc.
In researching this, I came across the claim that in Minnesota in 1995, 59% of the power returns from the consumer to the substation through the ground rather than the neutral wire. On the face of it, I find this number hard to believe, and am looking for an explanation.
The source was given as "Hendrickson, R.C., Mike Michaud and Alvin Bierbaum. 1995. Survey to Determine the Age and Condition of Electric Distribution Facilities in Minnesota: Report 1: Analysis of Overhead Distribution Feeder Testing Data. Minnesota Public Utilities Commission. May 18, 1995" but this does not appear to be available online.
I can think of a few potential explanations:
- Is SWER widely used in Minnesota? I found some mention in passing that SWER is used somewhere in the upper Midwest, but not where, specifically.
- Three-phase distribution systems out of perfect balance without a neutral wire would also cause ground current.
Are there any other explanations?
Best Answer
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.