Single Wire Earth Return

wrote:


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.
Bill
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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 .
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Don Kelly
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<snip>
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 ofcoordinates to another set (and not necessarily keeping power invariance asin 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.
Bill
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snipped-for-privacy@shawcross.ca wrote:

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.
daestrom
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J.B. Wood wrote:

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.
Thoughts?
daestrom
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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.
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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. -- Tom Horne
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Don I won't say that the effects poor secondary wiring never gets blamed on the power company but why does the power company get to say that the problems that the Multi Grounded Neutral system causes with livestock are actually caused by the multiple ground points on the farm when that was the acceptable wiring practice for decades. The power company's use of a Multi Grounded Neutral is not causing the problems that large animal veterinarians have documented but individual grounds on the Neutrals at each building on the farm does cause such harm? The reason I don't buy that is that when I have broken the Neutral pathway from the utility by opening the Neutral at the meter base the stray currents disappear. That was on two different dairy farms in widely separated locations. Mind you that turning off all power to the farm didn't make the stray currents disappear but opening the Neutral at the service point did. And when I temporarily installed an isolation transformer the stray current stayed gone. After ruining a dairyman's livelihood for almost six months he's supposed to except their explanation of a bad connection on the neutral and eat his losses? I'd have sued to. When the fence charger is not even connected but the cows won't go anywhere near the front fence line the clue phone is wringing. When production in dairy cattle jumps every time there is a utility service disruption and the rancher has to drag out his PTO driven generator the clue phone is ringing. And when I can measure ten or more amps of AC current on the Neutral with all of the Service Disconnecting Means except the Neutral connection open the clue phone is ringing. -- Tom Horne
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It is not allowed by the National Electrical Safety Code that is law in most states. However, for some very remote locations in Alaska it is used anyway. There is one up near the Seward Peninsula running across some really remote land according to the retired electrical contractor that put it in. He lives in Nome, Alaska and probably knows more about it than most people. His name is Fred Moody and you probably can get him by calling information for Nome Alaska. Also,it was used for years for a line along the Alaska Highway between Tok Alaska and Dot Lake. Finally an electrical inspector wrote it up. They then tied a bunch of abandoned overhead telephone wires together and used them for the earth return. When the Gas Pipeline crews were looking at building a gas pipeline along the the Alaska highway they were concerned for fear the metal gas pipeline would become the earth return. I have seen single lines with earth returns in rural British Columbia.
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I should add some tidbits about the retired line contractor living in Nome., Alaska. He also installed the overhead distribution system at Little Diomede Island near Russia and performed maintenance and redistribution of power lines to the gold dredges at Nome. He also was able to start the old gold company power plant left at Nome from about 1938. He is one of the most interesting persons I have ever met and is an Alaskan bush expert on supplying power to remote locations. When you meet someone like this you just wish they could transfer everything they know about power to the younger generation before they pass on.
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On 17 Mar, 10:41, "J.B. Wood" wrote:

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.
Owain
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