Single Wire Utility Transformers?

[mtnelect]

Close to Mongo's statement in Blazing Saddles.

Congratulations !

 

[tortuga]

Let's talk money

I think there is too much confusion of what system we are discussing here and what there alternatives are.
So I whipped together a 1-line that compares the two systems we are discussing side by side (as I understand them).
At the top of the 1-line is the substation (112 kV - 13.5 kv or whatever),
the neighborhood primary distribution and its protection relays.
Distribution transformers that drop to 120/240 split phase.
1-line ends at the customer service disconnect.
Next to each system is the parallel metallic underground piping and communications circuits that are presumed to be in parallel with all grounding electrodes along the way.

(A) Is the older style ungrounded delta substation distribution, with the two bushing transformers that is being slowly replaced across the US.
(B) Is the newer Multi grounded wye substation distribution (one bushing transformers) we are discussing here that @mtnelect does not like.
For purposes of discussion I also added two more systems:
(C) A NEC style distribution system where the HV neutral is only bonded at the substation and all services would be 4 wire.
(D) Is a system like they have in Japan ( possibly Germany and other countries) where the Neutral is left floating at the service and everything is ground fault protected or "residual current protected" (RCD).

At the bottom I included what NEC changes I think would be necessary for each system.
Since there are no earth return systems in neighborhood distribution I did not include them.

 

[electrofelon]

Nice diagram Tortuga. I think what you drew up helps make the point I have been trying to make that seems to keep falling on deaf ears. It's sort of the elephant in the room. That is that no matter what your distribution system is, and even if you were able to complain about it enough to get rid of the MGN, if you have a grounded premise wiring system, you are still going to have current running all sorts of things like pipes, messengers, communication lines, etc. If you want to keep a grounded system you are going to have to extreme lengths to eliminate stray current, and that would be:
1. Isolate the secondary grounded conductor from the primary grounded conductor if applicable, and do not ground it at the transformer /pole.
2. Only ground the secondary conductor at one location, presumably at the building served.
3. Unfortunately you would have to have a dedicated transformer for every building, you couldn't serve multiple structures from one transformer.

So that might "solve" one problem, but that type of system would have other issues, such as high expense for the large number of transformers needed, less grounding which may not be as good for transients, lightning, and contact with higher voltage lines.

So maybe ungrounded is the way to go, but that of course has issues as well.

 

[tortuga]

Nice diagram Tortuga. I think what you drew up helps make the point I have been trying to make that seems to keep falling on deaf ears. It's sort of the elephant in the room. That is that no matter what your distribution system is, and even if you were able to complain about it enough to get rid of the MGN, if you have a grounded premise wiring system, you are still going to have current running all sorts of things like pipes, messengers, communication lines, etc. If you want to keep a grounded system you are going to have to extreme lengths to eliminate stray current, and that would be:
1. Isolate the secondary grounded conductor from the primary grounded conductor if applicable, and do not ground it at the transformer /pole.
2. Only ground the secondary conductor at one location, presumably at the building served.
3. Unfortunately you would have to have a dedicated transformer for every building, you couldn't serve multiple structures from one transformer.

So that might "solve" one problem, but that type of system would have other issues, such as high expense for the large number of transformers needed, less grounding which may not be as good for transients, lightning, and contact with higher voltage lines.

So maybe ungrounded is the way to go, but that of course has issues as well.

Thank you, while I personally dont even have an opinion on the matter, its important for us to agree on what the topics are in question.

 

[ramsy]

Nice diagram Tortuga.

Roger that. Nice work Tortuga.
Wikipedia has a comparison chart between these earthing systems.

View source for Earthing system - Wikipedia

en.wikipedia.org

The chart shows TN-S as safest, but only TT removes parallel paths of objectionable current.

 

[drcampbell]

I have posted this before, and everyone thinks this is BS. Except for me.

Page 6 seems to be missing.

 

[mtnelect]

I think there is too much confusion of what system we are discussing here and what there alternatives are.
So I whipped together a 1-line that compares the two systems we are discussing side by side (as I understand them).
At the top of the 1-line is the substation (112 kV - 13.5 kv or whatever),
the neighborhood primary distribution and its protection relays.
Distribution transformers that drop to 120/240 split phase.
1-line ends at the customer service disconnect.
Next to each system is the parallel metallic underground piping and communications circuits that are presumed to be in parallel with all grounding electrodes along the way.

(A) Is the older style ungrounded delta substation distribution, with the two bushing transformers that is being slowly replaced across the US.
(B) Is the newer Multi grounded wye substation distribution (one bushing transformers) we are discussing here that @mtnelect does not like.
For purposes of discussion I also added two more systems:
(C) A NEC style distribution system where the HV neutral is only bonded at the substation and all services would be 4 wire.
(D) Is a system like they have in Japan ( possibly Germany and other countries) where the Neutral is left floating at the service and everything is ground fault protected or "residual current protected" (RCD).

At the bottom I included what NEC changes I think would be necessary for each system.
Since there are no earth return systems in neighborhood distribution I did not include them.

Thank you for taking an interest on the subject of MGN and trying to decode this complicated issue.
Attached is the feed from SCE to my service.

 

[mtnelect]

Nice diagram Tortuga. I think what you drew up helps make the point I have been trying to make that seems to keep falling on deaf ears. It's sort of the elephant in the room. That is that no matter what your distribution system is, and even if you were able to complain about it enough to get rid of the MGN, if you have a grounded premise wiring system, you are still going to have current running all sorts of things like pipes, messengers, communication lines, etc. If you want to keep a grounded system you are going to have to extreme lengths to eliminate stray current, and that would be:
1. Isolate the secondary grounded conductor from the primary grounded conductor if applicable, and do not ground it at the transformer /pole.
2. Only ground the secondary conductor at one location, presumably at the building served.
3. Unfortunately you would have to have a dedicated transformer for every building, you couldn't serve multiple structures from one transformer.

So that might "solve" one problem, but that type of system would have other issues, such as high expense for the large number of transformers needed, less grounding which may not be as good for transients, lightning, and contact with higher voltage lines.

So maybe ungrounded is the way to go, but that of course has issues as well.

That's the main problem with MGN, you are tying every home on that one transformer together. A neighbor that is having a problem, becomes your problem also. It's a great solution for the utilities but causes major problems for the consumers.

 

[electrofelon]

That's the main problem with MGN, you are tying every home on that one transformer together. A neighbor that is having a problem, becomes your problem also. It's a great solution for the utilities but causes major problems for the consumers.

Apparently you still do not understand that you would have the same even issue without an MGN. As long as the secondary is a grounded system and one transformer serves multiple buildings, then every home will be tied together and currently will flow on pipes, messengers, etc. . May I suggest spending a few minutes and drawing it out, maybe that will help .