Stray Voltage

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It sounds like the manual is saying that the Z of the entire fault path is 50 ohms, 40 from the impedance of the line and tower which is in series with 10 from the ground rod.

The result, before the person touches the tower is Ifault= 5000V/(40+10) = 5000/50 = 100A. This means that the voltage drop across the impedance of the line and tower is 100*40 = 4000V, and the voltage drop across the ground rod is 100*10 = 1000V.

When a person touches the tower they create a parallel path, with the 10 ohms of the ground rod. This new parallel resistor is in series with the 40 ohms of the tower and line, so the touch potential is only 1000V.

Clear as mud, but typical of the short cuts taken by a writer when they are trying to reach a specific conclusion.
 
jim dungar said:
It sounds like the manual is saying that the Z of the entire fault path is 50 ohms, 40 from the impedance of the line and tower which is in series with 10 from the ground rod.

The result, before the person touches the tower is Ifault= 5000V/(40+10) = 5000/50 = 100A. This means that the voltage drop across the impedance of the line and tower is 100*40 = 4000V, and the voltage drop across the ground rod is 100*10 = 1000V.

When a person touches the tower they create a parallel path, with the 10 ohms of the ground rod. This new parallel resistor is in series with the 40 ohms of the tower and line, so the touch potential is only 1000V.

Clear as mud, but typical of the short cuts taken by a writer when they are trying to reach a specific conclusion.
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Well finally that is correct thank you for your help , I really felt like a complete lost puppy all day but yes thats exactly how the manual shows it all we were saying was low resistance to earth is better in some grounding areas and i think this might work even with a lower voltage what do you think ? comments best to ya
 
ohmhead said:
you are not understanding the 40 ohms Z impedance is in the line the transmission line not the ground rod the short to tower ground the line
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Yes I do, it forms a simple voltage divider circuit which is what we are trying to tell you. Problem is that ten ohms you are referring to is well below grade at the last half of the rods that are deepest in the ground. Above ground level where someone is likely to make contact is above ground and exposed to much higher voltages that what you think.

Now let me ask you this in that assumption of 40 ohm transmission circuit. What is the value of the fuse or breaker? Is it 100 amps, 150, 200, or what? Most transmission lines I designed years ago are a lot more than 100 amps, and a 100 fault looks like a load current to me and the circuit protector. Only thing that would react is a differential trip and then reclose after it blows you clear of the circuit.
 
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Its bang on in that dairy farms are a special case where stray currents are a nightmare.

The real problem is that 250.30 requires the importation of the supply ground through a bond to the load ground, which, under some circumstances, like a milking shed, is a really poor idea, so you cant even do what the rest of the world does, and just bung in an isolating transformer to stop daisy being tingled.
 
dereckbc said:
Now let me ask you this in that assumption of 40 ohm transmission circuit.
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I think, the problem is the example in the manual has nothing to do with the real world. The writers simply intended to show how a very basic voltage divider works, they chose unrealistic values to make the math easy.
 
Well yes they did not intend to give relaying protection or pilot relaying overreaching diff ect ect .It was just a example of a condition , to show touch voltage within reach . not all faults trip on distance lines or you can have a minor cross of high voltage to a metal object for months or days if its stable and comes up slowly to a limit and not know it until that insulator breaks down or air gap opens or wind picks up and blows out the tracking or spark gap .There lots of stuff i dont know but i learn everday i just go by what i read and see each day . lets just leave it at that ,thanks for the time it was fun i like debates but this ones over . best to ya take care iam just a electrician not a engineer sorry i could not be better at answering you questions.
 
Stray Current - not Stray Voltage # 35

Stray Current - not Stray Voltage # 35

1-25-09 11:16 am # 35
Stray Current - not Stray Voltage
________________________________________
Charlie Eldridge, Indianapolis, Utility Power Guy wrote-
?This is really about Stray Current - not Stray Voltage. I have never understood why it is called Stray Voltage by most people.?

Donald W. Zipse, P.E., IEEE Life Fellow replies:

The following is from a technical paper presented at the Institute of Electrical and Electronic Engineers? Petrouleum and Chemical Industrial Committee conference titled, ?DEATH BY GROUNDING?, Copyright Material IEEE, Paper No. PCIC-2008-03. (The paper was given to Mike and may be on his web site.)

?As a side comment Edison did not call his type of electrical distribution system Direct Voltage, but Direct Current. Likewise, Nikola Tesla and George Westinghouse called their type of electrical system Alternating Current, not Alternating Voltage.

?Anyone placing two leads of a voltmeter into the earth is likely to measure a voltage. Before 1950, it is opined new employees of utility companies were given relative low cost voltmeters instead of expensive ammeters enabling them to make voltage measurement anywhere in the earth instead of current measurements. The author was 30 years old with 14
years of electrical experience before obtaining an ammeter because of the high costs.?

It is easier to measure voltage than current in the earth.

Donald W. Zipse, P.E.,
IEEE Life Fellow
 
Stray Current - not Stray Voltage # 35

Stray Current - not Stray Voltage # 35

1-25-09 11:16 am # 35
Stray Current - not Stray Voltage
________________________________________
Charlie Eldridge, Indianapolis, Utility Power Guy wrote-

?Consider that Zipse wants the entire US distribution system changed from a wye to a delta configuration. All of the existing transformer will have to be junked and replaced with higher voltage primary coils and this is just the start. Just installing a grounding conductor would be prohibitive since, in many cases, taller poles would be required. All underground cables would have to be replaced where only one phase exists.?

The above statement is completely wrong, incorrect and has never been voiced, written or testified to in court.

What Donald W. Zipse has said is the multigrounded neutral distribution system should have the single conductor that is referred to as a neutral which actually is a combined neutral (white) conductor and equipment grounding (green or bare) conductor separated into two separate conductors. The existing multigrounded neutral which is connected to earth 4 times per mile and at each transformer should be used as the ?equipment grounding conductor?. This multiple connections of the neutral to earth allows uncontrolled current to flow uncontrolled over the earth harming humans, cows, pigs and dogs.

An additional conductor should be installed that would be an isolated and insulated neutral conductor the same as is used in homes, commercial and industrial buildings. This distribution system would be the same as the readers of this Forum are familiar with if they ever wired an industrial building or office building.

Such a distribution system would have the same wiring as the above buildings ? 1, 2 or 3 phase conductors ? an insulated and isolated neutral conductor and an equipment grounding conductor.

The very same transformers if two bushing would be used ? the multigrounded neutral would be replaced with the insolated neutral conductor. Higher voltage would not be required. Taller poles would not be required, in fact the same poles would be used.

An example is a case in New Jersey when to solve the stray current problem a so called expert for the utility said the multigrounded neutral needed to be replaced with a larger sized conductor (Example Replace # 4 AWG with a 250 MCM) D. W. Zipse is quoted in the local news paper as stating it would not solve the problem. The next summer stray current was still prevalent and Georgia Tech experts called to replace the original expert, agreed with me, that installing a larger conductor would not work.

The cost for 7,000 circuit feet was $ 250,000.00. For the same cost the system could have be converted to a safe 5 wire system.

Donald W. Zipse, P.E.
IEEE Life Fellow
 
Donald, thanks for revisiting this issue. :cool:

I have a question: how much do you anticipate it would cost for utilities to modify their distribution systems to include an EGC? I'm no utility guy, but I can imagine the cost to reconfigure all wiring between the utility generator to the end consumer would be astronomical.

Contrasting this imagined (yet unknown to me) cost against the benefits of reduced stray voltage (which in my mind are little to no life safety improvement, minor increases in agricultural production and minor reductions in service calls to agricultural and recreational facilities), and I see no impetus to change the existing system.
 
You could start by installing new transformers phase to phase only. Ok, it'll take a century, but eventually MGN will be gone.

George Stolz said:
Contrasting this imagined (yet unknown to me) cost against the benefits of reduced stray voltage (which in my mind are little to no life safety improvement, minor increases in agricultural production and minor reductions in service calls to agricultural and recreational facilities) ...
Click to expand...

The differences in agricultural production are not minor but are astounding.

Though, to be fair, most agricultural stray current problems could be fixed at very low cost by adjusting the NEC.
 
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