Another thought that came to mind about this is the cost of wire versus the total cost of the line.
Using SWER cuts the wire costs in half, but doesn't change the number of poles needed. If the second wire is a multi-grounded neutral, there is no cost of insulators for this wire.
In the Australian outback, I can imagine the cost of poles or towers is higher than in rural North America where wood poles are easier to come by.
But this would argue against SWER versus traditional two wire since the savings would be a smaller percentage of the line's total cost.
I suppose it depends on how sensitive Moose are to stepping potentials. I am sure there are potentials in the earth for the distance between the moose feet. Based on the elaborate NEC requirements for equipotential grounding for agricultural buildings to prevent cows from not giving milk I would hypothesize that the cathodic protection systems can cause a problem even at the realtive low voltages. It should at least deserve a stimulus grant for study. The Agricultural people at the University of Alaska recently got a stimulus grant of 1/2 million dollars to study a foreign weed called white sweet clover that has invaded Alaska. The electrical engineering department should get the same amount of money to study the effects of cathodic protection systems on moose (hint).
It wasn't the farmers who did this-the utility would run a 6900V hot wire and at each service point the transformer was (and still is) connected from this to ground. The ground current would follow the line but its spread would be dependent on soil conditions. I am going from recall in the late
40's, early 50's when rural electrification was new and growing at a great rate. Your NZ paper indicates 1947 which is in that period- and the practice was used by North American utilities such as the then Calgary Power and Canadian Utilities in Alberta and Saskatchewan. If I recall correctly, the first such rural system in the region was installed about 1947 in Swalwell, Alberta. (I am assuming that you are familiar with these names -guessing from your service provider) However, the practice didn't last long (to the mid 50's or so) before a return wire was installed (in parallel with the ground path) so potential problems were recognized.
I hope that I didn't imply that the farmers used the ground as neutral. ----- Don Kelly (also P.Eng retired) cross out to reply
As I recall, the ground wire when used is typically mounted on a small metal bracket which is cheaper than an insulator. As for questions regarding the cause of stray voltages- I recall that courts in Wisconsin agreed with the farmers. The effect of ground currents will depend on the location of the line with respect to the farmers buildings -noting that AC ground currents follow the line and the effective spread of current is dependent on soil conditions. Certainly Tom Horne's comments are not to be ignored although I am not fully convinced at this time I must admit that other than studying an analysis about 30 years ago, I haven't been involved with this problem - nor have I heard of it being a problem in the area where I lived.
All First off let me apologize for the confusion I've caused by hijacking a thread that was about single wire ground return rural utility distribution into a discussion of stray current on two or four wire Multi Grounded Neutral (MGN) distribution.
Don What made me a believer that this problem was real was the absolute intransigence of the utility that was providing power to the two ranches; or dairy farms if you prefer; were I had to solve the problem. A company doesn't stonewall that fiercely unless they have something to hide. The fact that production went up sharply on both farms when the neutral was opened at the service point and that I could measure current flows as high as fifty amperes on the neutral with the farms service disconnecting means open was all I needed to see to convince me that the problem currents were originating on the Multi Grounded Neutral (MGN) of the utility.
At the first farm I installed an isolation transformer. The problem disappeared and production went up by more than 25%. With that as evidence the farmer filed suit against the Utility and they settled out of court. The farmer was so delighted with the change in the animals that he gave me a several hundred dollar bonus back when that was pretty serious money. When I opened the Neutral in order to confirm the source of the current the stock became positively playful. When his wife saw the change she broke down in tears. The problem had been getting worse over the course of two years. The utility eventually found and repaired a bad neutral splice but they still tried to deny any responsibility for the losses to the affected farms.
At the second farm as soon as I confirmed that the current was coming from off premise I got the local Delegate / Assemblyman involved and through them the Public Utility Commission. When the PUCs Electrical Engineer witnessed my testing he turned to the utility's representative and said two words. Fix it! The utility twerp turned to me and said what do you want to see. I said a service open Neutral current in excess of one ampere was unacceptable. They got it down to under one ampere and made the farmer whole based on his production receipts from the milk transport company. By settling promptly they kept the lawyers and punitive damages out of it. Amazingly enough after the second farm all I had to do was call the utility to get a real EE out to any site I was having a utility problem with whether or not that property was agricultural. As for the business office twerp I had to start with in both cases all further calls from me were referred directly to the engineering section.
None of this is meant to say that the on premise wiring was never at fault because I fixed several of those as well. Watching a dairy cow trying to dip water out of her stalls watering cup with her tongue without touching the metal cup is a uniquely painful experience. Grounding electrodes do corrode when they are bathed constantly in urea. Ground faults on old two wire branch circuits are not necessarily self clearing. My point is that it is not always the secondary wiring that is the source of the stray current.
When I took myPE exam, it was the first time in a long time when it had no problem on symmetrical components in a long time. In many ways, that is now passe. At UCLA now, for example, AFIK, there is not even a mention of symmetrical components or even three-phase in the EE course.
Undergraduates now get at least one intensive course in linear systems which includes much of linear algebra and matrices. The symmetrical components reduces to a subspecialty of eigenvalues and eigenfunctions using complex functions including the operator corresponding to the cube root of -1.
Is this a good trend. I do not know. It may be a good mathematical background with much application. On the other hand, most of the students are not likely to know how to use a soldering iron. Color code--what is that. Being a radio amateur these days would seem to be unrelated to be preparation for electrical engineering. Figuring out what to dow with a wound rotor induction motor is not going to be a career enhancer.
Actually, as I understand cathodic protection used on mothballed Navy ships, you don't need very much current at all. The idea is to apply just enough voltage to counteract the voltage created naturally by the dissimilar metals in an 'electrolyte'. You could *theoretically* tune it to exactly counteract this potential so no galvanic current flows and no corrosion occurs.
I mean, the stuff the Navy used to protect ships in long term storage was in the mA range. Too high a current and your electrode corrodes away faster than the hull would rust if you have nothing at all. Then you just have a bare wire touching the water line and less protection.
I'd imagine the same is true for this set up, you want a small potential developed to counteract the natural galvanic action, but it doesn't have to be any sort of massive current.
I think that your response was directed to another thread -re symmetrical components rather than single wire earth return. In the last 40 years, there has been a change in EE curriculum such that many schools don't deal with the "power" side. There are still schools that do still include such things as power systems, symmetrical components, etc in both the US and Canada. Still important but low on the glamour scale. Do any engineering schools, with or without 3 phase, deal with the use of soldering irons- did they, even in the '50's? It seems to me that this was something you picked up. If you want a bad trend- some even replace circuits labs with "virtual labs" or computer simulation of a circuit.
Somehow, I never considered symmetrical components in terms of eigenvalues and eigenfunctions but simply as linear transforms from one set of coordinates to another set (and not necessarily keeping power invariance as in direct/quadrature axis models for machines). Of course much of the utility of symmetrical components is that except for untransposed lines, mutual coupling between the sequence impedances of an element are 0 or too small to worry about. It is interesting that Fortesque's original paper is now summarized in a fraction of the printed space- it originally took about 1/3 of the year's AIEE transactions- a very long paper .
I indeed erred and got my strings crossed, I am reposting.
My comments on linear systems still stand. Your comment about ". . . but simply as linear transforms from one set of coordinates to another set (and not necessarily keeping power invariance as in direct/quadrature axis models for machines)." reminds of something from a Moliere play that included "Here I have been speaking in prose all these years and didn't even know it." The use of matrices and tensors in engineering goes back a long time. That IS the essence of linear algebra, Civil engineers developed Mohr's circle because they did not study tensors. The in-phase and quadrature components of impedance allow the use of a tensor idea without actually using the term. In fact, until discussing tensors here, I did not realize the use of in-phase and quadrature impedances were indeed tensors on the cheap. Were you ever exposed to the concepts of Gabriel Kron?
In symmetrical components you deal with a vector with three complex components, each describing the amplitude of one of the phase sequences. In this case, the three eigenvalues are the cube roots of -1. Much of what is now done at an undergraduate level was at a graduate level in my day.
As an undergraduate, I did not really know much about tensors. When it really gets down to understanding piezoelectricity, you have to understand that dielectric constant is a tensor as is the elasticity in (frequency control) crystals.
I got a fair amount of machinery labs as an undergraduate. Not much soldering in electronics or radio. I learned to solder fairly quickly with a part time radio shop job when I was in high school. At the time I could not personally afford an electric soldering iron. For about 30¢ I got one I could heat in a gas flame on the kitchen range. Needless to say, my first soldering attempts did not wet the conductors.
I've noticed that a lot of the 'on-line campuses' are going this route. Of course not all on-line schools are the same caliber, but 'virtual labs' provide some amount of 'hands on' even in the on-line schools.
Not the same as burning your finger with a real soldering iron, but somewhere in between real physical labs and just classroom/book learning.
Single wiring with combined earth and neutral used used to be allowed in British domestic installations provided that earthed concentric wiring (eg single core mineral-insulated copper-clad) was used and it was from a private supply not connected to the public mains.
On the distribution side it (and electric tramlines) used to cause havoc with telephone wiring, so was probably ceased c. 1920 if it was ever used.
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