high voltage utility lines

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kwired said:
Step potential depends on how long the step is. 20 volts around dairy cows is way too high, in fact it is more than a production issue at that level, it is likely dead cows everywhere at that level.

If same system were used near a marina, or even where private docks with power exist, there would likely be dead swimmers found around the docks quite frequently. I don't care how much primary conductor it saves it is a poor design IMO.
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I am not convinced about your concerns because

1) The grounding and bonding rules of the NEC may be sufficient to afford enough protection in such cases.

2)Such a single wire earth return (SWER) power system was successfully installed in 1981 from a diesel plant in Bethel to Napakiak in Alaska,United States. It operates at 80 kV.
 
Sahib said:
I am not convinced about your concerns because

1) The grounding and bonding rules of the NEC may be sufficient to afford enough protection in such cases.

2)Such a single wire earth return (SWER) power system was successfully installed in 1981 from a diesel plant in Bethel to Napakiak in Alaska,United States. It operates at 80 kV.
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I have no doubt it works, grounding and bonding rules of NEC actually make conditions worse in some cases, and it is a definite problem particularly with dairy farmers even when there is a little impedance in a typical multi grounded neutral.

Step potential for a person is shorter than it is for a cow, plus they are standing in/on urine, water, and other waste with no shoes, boots or other electrical insulation. And if they are touching a metal object with their mouth/nose it may be even farther distance from that point to their back feet meaning more potential voltage. Fairly low voltages will cause a drop in milk production and even cause health issues with the cows. If the voltages are high enough they will feel it and this can cause them to not even want to approach feed or water or enter the milking parlor or other areas which makes even more problems for the dairy farmer.

Many times there is a problem the cows can feel but people can not - partly because we do not stand in same conditions barefooted with four feet on the ground - and with such a spread between feet. Following NEC helps minimize potential but does not make this current go away. When you have animals that weigh 1000 pounds or more, nothing ever gets broken either - just ask the people that work in these places and they will disagree.

The more earth connections there are in the system you have the more stray paths potentially can develop. If the earth return is from one single point to another single point (the point here may be a large point) then you have a different situation than if you have multiple connections to earth and every one of those is bonded to premises wiring systems.
 
kwired said:
I have no doubt it works, grounding and bonding rules of NEC actually make conditions worse in some cases, and it is a definite problem particularly with dairy farmers even when there is a little impedance in a typical multi grounded neutral.

Step potential for a person is shorter than it is for a cow, plus they are standing in/on urine, water, and other waste with no shoes, boots or other electrical insulation. And if they are touching a metal object with their mouth/nose it may be even farther distance from that point to their back feet meaning more potential voltage. Fairly low voltages will cause a drop in milk production and even cause health issues with the cows. If the voltages are high enough they will feel it and this can cause them to not even want to approach feed or water or enter the milking parlor or other areas which makes even more problems for the dairy farmer.

Many times there is a problem the cows can feel but people can not - partly because we do not stand in same conditions barefooted with four feet on the ground - and with such a spread between feet. Following NEC helps minimize potential but does not make this current go away. When you have animals that weigh 1000 pounds or more, nothing ever gets broken either - just ask the people that work in these places and they will disagree.

The more earth connections there are in the system you have the more stray paths potentially can develop. If the earth return is from one single point to another single point (the point here may be a large point) then you have a different situation than if you have multiple connections to earth and every one of those is bonded to premises wiring systems.
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You are referred to

http://forums.mikeholt.com/showthread.php?t=155359&p=1503322#post1503322
 
fmtjfw said:
In areas of sparse population in Canada, they use a single primary wire and an earth return for the other primary conductor. Consider a primary voltage of 13kv (wild guess) and a 10kw load, the current in the primary would be 10/13 or less than an amp. Now with an earth ground resistance of 20 ohms, the step potential voltage drop would be less than 20v. This saves them half the cost of primary conductor.
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It is a matter of engineering economics. If you can only invest $x for a single customer, if a pole line costs $a for poles per mile and $b for a single conductor and $b*2 for two conductors, then the maximum distance for a single primary service is $x/($a+$b) which is longer than $x/($a+$b*2) for two conductors.

You can serve more customers using a single primary.
 
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