A Dairy Farmer’s Response to Jim Burke’s Paper
PLEASE NOTE THAT I HAVE THE HIGHEST REGARD FOR JIM AND ADMIRE HIM GREATLY –but when it comes to my dairy cows, I very respectfully disagree with portions of the paper presented in this forum.
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Jim Burke and I co-authored a paper on this very subject a couple of years ago, it was chosen as a prize paper and published by IEEE.
The paper referred to in this forum was published by Jim before our joint paper.
While Jim and I did not agree on many issues, we did agree that dairy farms deserve extremely effective isolation and our paper dealt with many of the issues Jim presented in this earlier paper.
Please keep in mind that the following comments are those of a dairy farmer and are not to be considered electrical engineering or electrical advice, it is simply my understanding. They are only stated “in my humble opinion”, as a dairy farmer.
Jim makes some statements in this paper that I disagree with and I will point out a few for you below.
Areas of Disagreement:
1st. “And finally, although everyone knows that current kills…not voltage, “stray current” and “stray voltage” are not directly related…at all.”
Anyone that understands stray voltage in dairy animals and Ohm’s Law as it applies in stray voltage/current knows that without all 3 components, stray voltage/current does not exist; it takes Resistance, Voltage and Current.
I actually prefer the term stray voltage/current because it is then the resistance through the cow that is the 3rd element required to meet/satisfy Ohm’s Law. (Please see the quote later from 696)
2nd. Stray voltage/current associated with dairy animals can be from the following sources, normally listed in two categories as “On Farm” and “Off Farm”.
“Off Farm” sources such as Primary Neutral to Earth Voltages create Earth Currents that may access the dairy cow’s environment, because they use earth and all associated conductive paths in completing the circuit back to their source, the substation. Earth Currents can be from the normal current associated with the grounding utilized in a Multi-grounded Neutral Wye Distribution System.
It should also be noted that of all the Non Standard but Approved Distributions listed in the 2002 Cooperative Research Network Publication by the National Rural Electric Cooperative Association entitled “Stray Voltage-Analysis and Mitigation”, authored by NEETRAC, it is clearly stated that the only distribution, of those listed in this Stray Voltage manual, that causes stray voltage by design is the multi-grounded neutral wye distribution. All of the other distributions listed do not, by design, create Primary Neutral to Earth Voltage which in turn create
Earth Currents and thereby may create stray voltage/current concerns. Earth currents can also be from overvoltage conditions, faults and/or leakage which also enter earth.
“On Farm” sources can be from the farms’ secondary distribution system when the grounding of the secondary distribution allows normal secondary neutral current, overvoltage conditions, fault current and/or leakage current to access the dairy animals on their paths back to the source transformer for the farm.
It should also be pointed out that if the secondary distribution is properly wired as a 4-wire single phase or 5-wire 3 phase secondary distribution, you will not, by design, create Secondary Neutral to Earth Voltage.
In old farm 3-wire single phase or 4-wire 3 phase secondary wiring systems the grounding conductor (ground) and grounded conductor (neutral) between the source transformer and a Service Entrance Panel was one and the same conductor; this conductor was grounded at both the farm or source transformer and the Service Entrance Panel. This created secondary neutral voltage drop, which allowed normal secondary neutral current to divide due to the resistances provided by this grounding and the resistance of the conductor. The resulting voltage/current was free to use earth and all associated conductive paths back to the source transformer, which may create a stray voltage concern.
The Newer 4-wire single phase or 5-wire 3 phase secondary utilizes an additional secondary conductor for the circuit so you now have the grounded conductor (neutral) and the grounding conductor separate all the way back to the transformer area where the two are bonded.
With a proper 4-wire or 5-wire integrity check, you can reduce On Farm sources to the grounding conductor and it can be monitored for correction of leakages, faults and over voltage conditions. By wiring correctly and with extremely effective isolation from the Primary Neutral as allowed by the NESC, you can have an extremely low level of stray voltage/current from On Farm and Off Farm sources.
3rd. To clarify one of Jim’s statements, it is a known fact that it is the Peak Current that affects the dairy animals, not simply the current as Jim states. (His statement is not incorrect, simply not complete in a significant detail.)
4th. Voltage is measured in Stray Voltage/current concerns because it is the easiest to measure for the untrained investigator. When we work with the dairy farms’ electricians and engineers to correct a stray voltage/current concern, we look at both the voltage and the current, not just the voltage and guess what, when you correct the fault and leakage currents, and are extremely effectively isolated from the Primary Neutral, you make the cows happier.
5th. “Stray Current—I’ve heard the term-“Stray Current” in recent years and really do not know what it is”.
Once voltage and resistance cause current to leave the designed metallic electrical circuit conductor and enter earth, I submit it is Stray Current because you lose control of it and it uses all paths in inverse proportion to the resistance of the path, to return to the source transformer. Voltage is simply the “pusher” of the current—if you remove the “push” (voltage), you do not have the current and guess what—you also do not have
Stray Voltage or Stray Current.
6th. “It would appear that some of those using this term are saying that any current entering earth is really stray current, the implication being that it wasn’t supposed to go there. Such nonsense!”
Jim, answer one single question for me, please. When this current enters earth, do you have control over it when it is in earth or does it take all paths in inverse proportion to the resistance of the path on its journey back to the source substation? I believe it is also extremely important to note that God did not put the AC current there, man created AC electricity and put it into earth. While DC voltage/current is part of nature, AC is not.
I believe you do not control it, and it is when this current causes discomfort to the dairy animal while taking its journey back to the substation through the dairy farm that I become extremely concerned. Remember in our paper we agreed that the dairy farmers have a right to extremely effective isolation.
7th. I would suggest that concentrating on monitoring “stray current” is a waste of time”.
Simply stated I disagree. When you correct the current flow, the voltage is also gone and we have found the cows like it when we remove it—they become happier if we do an extremely good job of removing it!
Jim do you sense a really big disagreement coming—then you are incorrect –wait and see!!
“Figure #6, shows a distribution transformer where the primary and secondary neutrals are not connected. If this were the case, the utility would not see the majority of stray voltage complaints.”
I absolutely agree with you Jim, just as we did in our paper.
However, in the second part I agree and disagree with you. “However, the Code requires that the 2 neutrals be connected.”
As we agreed in our joint paper, the NESC also allows for isolation of the 2 neutrals, and the NEC also allows the dairy farmer to use a separately derived source to create his own neutral. This can also be accomplished by a transformation on the primary distribution, which is also listed in 2002 CRN.
And Now the Big Disagreement with Jim Burke’s paper.
“Figure #9, shown below, illustrates the impact of various levels of stray voltage on cows. As can be seen it takes about 5 volts to cause moderate activity.
First, I have no idea where you obtained this chart but it is unsupported by many highly reputable papers written by researchers in reputable universities. And those same highly reputable papers fly directly in the face of some other research papers written by researchers that testify for the utilities in litigation. In fact, I am personally familiar with one such researcher that signed an affidavit to the Court that was stricken, by the Court, because it was far less than completely honest or accurate. (My paraphrase, not the exact wording of the Court). (In my humble opinion, he more likely than not, perjured himself).
As we discussed, this type of chart is approximated in USDA 696 which is also referred to as the Red Book.
In 696 the authors took a giant leap of faith by stating clearly, the word “IF” and they also stated the resistance that would cause reaction in 90% of the herd, this is NOT the level an informed dairy farmer would agree with, provided he and/or she had a complete understanding of the chart’s statement.
In 696 they use the following charts which I cannot seem to have in this response because they are images:
The first chart lists the Norell work for mouth to all hooves, which is the most common cite and it lists the Resistance range of 244 to 525 ohms
MOST IMPORTANT:
Please note the foot note #3 lists Ranges are for 10-90 percentile, or percent of cows with measured resistance between the reported limits. The most commonly cited work was originally conducted by Norell and in personal conversations with him, he stated that the cows’ resistance in parlor/free stall environments, would be lower and any cut or break in the skin would reduce this resistance even more dramatically. Another researcher addressed this as well and used a reduction of over 50%.
The above cited chart simply means they COMPLETELEY disregarded the least resistive 10% of the dairy animals. I personally believe this is COMPLETELY WRONG AND IT IS ALSO WHY I HAVE TAKEN THIS OPPORTUNITY TO STATE THIS HERE.
Good dairy farmers want to protect all their animals, not just some of them.
In humans, Dalziel used the most sensitive ½ of 1% of the male population for SAFETY. Don’t our dairy animals deserve the same consideration for their SAFETY? I most certainly believe they do!!!
STRAY VOLTAGE/CURRENT
In 696 the Authors also stated the following:
“Cows are considered to be more susceptible to stray voltage/current than humans because cows have a lower body resistance.”
As you can see, the term stray voltage/current that I prefer is also stated in 696.
In 696 and the summary to 696 they simply are using the worst case level to affect 90% of the dairy cows and they then used an ADDITIONAL source resistance of 500 ohms to arrive at 1000 ohms which will allow one volt to push 1 mA through a dairy animal.
The second chart from 696 demonstrates how raising the resistance increases the amount of voltage to overcome the increased resistance. Every time the resistance is doubled the voltage to overcome it is also doubled. At one thousand ohms, 1 volt would push 1 mA through the animal, at 100 ohms, 1 volt would push 10 mA through the dairy animals. Jim’s chart does not show this correlation and it is the crucial element required.
“IF” we were to look at an early work of one of the researchers, he tested 7 cows and of the seven, one had a resistance of 216 ohms and another at 217 ohms. These 2 cows then represent 28.58% of the dairy animals in that study.
Using Ohm’s Law it is clear to see that at 216 ohm, 1 volt will push 4.629 mA through that dairy animal, which is NEARLY the 5 mA (5 volt at 1000 ohms) level you state it would take to cause a concern for you. Jim, as you and I discussed in writing our paper, in this situation it is the cows’ resistance that is the MOST important part to use appropriately so we make sure we are protecting ALL of the dairy animals.
To reiterate what I stated at the beginning of this response:
Please keep in mind that these comments are those of a dairy farmer and are not to be considered electrical engineering or electrical advice, it is simply my understanding and they are only stated “in my humble opinion.”
Chuck Untiedt - dairy farmer
Chuck Untiedt March 1 2011, 2:04 pm EST
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