Utility transformer primary neutral bonded to secondary

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mull982

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What would happen theoretically if the utility had a pole mount single phase transformer connected 7200kV L-N on the primary and 120/240V secondary, and they bonded the primary neutral to the secondary neutral. The netural from the secondary is brought inside your panel and bonded to ground/earth.

Now what if the utility transformer primary ever lost its neutral, would the transofmer still function through the primary neutral bonded to the secondary and then to earth in the panel? If so and you for some reason lifted the secondary neutral or ground, could you be subjected to the entire 7200V on the primary of the transfomer since the lifted neutral/ground would presnet a higher impedance (voltage divider) than the primary windings?
 
This is a very complex question that needs to be divided up in order to make better sense.

mull982 said:
Now what if the utility transformer primary ever lost its neutral, would the transofmer still function through the primary neutral bonded to the secondary and then to earth in the panel?
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Yes, the ground rod would become the reference point for the voltage function at the primary line. Ohm's law always applies, but in this case, it becomes more obvious because the voltage of grounding system will vary more depending on the resistivity of the physical earthing connection. The primary will get less than the full 7200, and the actual value will depend on the resistivity of all common grounding paths and the actual current flow (if any).

mull982 said:
If so and you for some reason lifted the secondary neutral or ground, could you be subjected to the entire 7200V on the primary of the transfomer since the lifted neutral/ground would presnet a higher impedance (voltage divider) than the primary windings?
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This is actually more straightforward because you have simply lost your G-N bond. With nothing to "anchor" the secondary, it is simply going to float to the voltage of the primary. Normally it would float somewhere in between the primary N & L, but since the primary already lost its N, then the secondary would go straight to the line voltage. All points in both the primary and secondary would become equal potential, and the only potential they have available to them is the primary line voltage. By Ohm's Law, because no current is flowing there will be no voltage difference, so everything is going to jump to line voltage.

Because this is magnetically coupled, it doesn't take much to bring the secondary voltage back down from 7200V, but at that energy level, you will still get bit pretty hard in the near-instantaneous process.
 
Rick Christopherson said:
This is a very complex question that needs to be divided up in order to make better sense.
Click to expand...

I guess I was referring to a stray voltage situation on a farm where transformer primary neutral is bonded to secondary and therfore there can be stray voltage on the ground. I was then wondering what happens to this stray voltage when neutral on primary transfomer is lost.
 
My apologies to our host, Mike Holt, but he does a great disservice to his students in the manner in which he teaches some of his topics regarding ground and neutral, and the multi-faceted functions they perform. It is a very complex topic, but from those excerpts I have seen/read, he leaves it at too high of a level for fear of over-complicating the discussions for the particular audience. That is necessary in order to not lose the audience, but he should at least acknowledge that there is more going on that what he describes. For example, in the video posted above (I watched the first several minutes), he makes the false assumption that the Planet Earth is an equipotential reference. It is not. There are natural voltage gradients throughout the entire planet that have nothing to do with mankind. They will always be there, regardless whether we connect our electrical systems to the earth or not. Ignoring this isn't necessarily bad on the face of it, but it also ignores some of the underlying principles surrounding the topics as well.
 
Rick Christopherson said:
My apologies to our host, Mike Holt, but he does a great disservice to his students in the manner in which he teaches some of his topics regarding ground and neutral, and the multi-faceted functions they perform. It is a very complex topic, but from those excerpts I have seen/read, he leaves it at too high of a level for fear of over-complicating the discussions for the particular audience. That is necessary in order to not lose the audience, but he should at least acknowledge that there is more going on that what he describes. For example, in the video posted above (I watched the first several minutes), he makes the false assumption that the Planet Earth is an equipotential reference. It is not. There are natural voltage gradients throughout the entire planet that have nothing to do with mankind. They will always be there, regardless whether we connect our electrical systems to the earth or not. Ignoring this isn't necessarily bad on the face of it, but it also ignores some of the underlying principles surrounding the topics as well.
Click to expand...

I understand what you are saying, but it doesn't need to be made as complicated or as far as you are taking it. I do not believe that earth surface voltage gradients will be enough to bother him, or his cows. After all, ESVG's were here long before we were. I am not as educated as you are, but I have never heard of anyone getting shocked by step potential from earth surface voltage gradients. Would this not be the same reason we have to go through all the extra equipotential steps for a pool? I believe he is referring to stray voltage that is common in most agricultural operations, especially milking operations. I merely posted the video as a tool for him to use to see if it would answer some of his questions. With this type of question, evidently something has happened and he is searching for an answer before he confronts the utility. ;)
 
I wasn't suggesting that a natural voltage gradient would be impacting livestock. I was merely pointing out that ignoring this concept is the same foundation as assuming that there is only a single cause for gradients. Too many members here believe that stray voltage can only be attributed to the utility system and faults therein. To the contrary. If we shut down every generator in the country, but left the grid in place, we would still have significant gradients in place, because the conductors are spanning non-equipotential surfaces. In other words, our grid is "trying" to make the earth equipotential, but it is not equipotential.
 
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