Finding the direction of AC current flow

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Whoops, sorry. Shouldn’t have said that.
open ended bet with no winner.. ever.
Neither one of us will have great great grandchildren that will remember what the bet was for anyway...

Existing might remain where surviving, but new construction will be phase to phase.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
that does not seem to be the case now, for decades there's been a strong trend toward MGM systems as you surely know. Why do you think this will revert back? Or are you saying it will still be mgn but with single phase transformers fed phase to phase?

Soon enough given the greater awareness of cause and long rather short term effect, along with an ever increasing understanding of human rights, phase-phase primaries will begin to become the norm. I doubt we will ever see true ungrounded supplies at the 230kv-13.8kv substation, more likely a wye supply with an MGN with all 13.8kv load connected phase to phase or in delta. California put into law that any current carrying conductor must be treated as if it were live in the early 90s (PUC-95) along with various committees dealing with EMF further pressing utilities to adopt practice which reduce parellel current paths. Stray voltage is mostly unheard of in California farms. Contrary to what utilities say the bulk of NEV comes from the POCO's MGN and POCO created earth current, not the farm's wiring.

There is an exception though, if phase-phase utilization became the norm 3 phase wye-wye transformers could be used in theory without passing significant neutral current however I can't see such a system catching on long term once 240 volts becomes the norm. 240/416Y 3 phase 5 wire will naturally become the new standard based on simplicity and efficiency requiring a delta primary. 120/240 and 138/240Y will simply fade out. Wye-wye has advantage of being resisitant to Ferroresnonance however because 416 volts can travel some distance transformers will be larger with far more diversity (always loaded to at lest 10%) damping out ferro at 23 and 34.5kv.


Here is how its typically done at 416 volts vs 120/240 and 120/208Y, notice the size of the units:


 

Xptpcrewx

Senior Member
Location
Las Vegas, Nevada, USA
Occupation
Power System Engineer
Let’s not forget the main benefits/reasons of connecting transformer primaries line-to-neutral instead of line-to-line... improved voltage regulation and ability to re-ground the system remotely via the transformer or transformer bank.

With line-to-line primaries, the voltage would be very unbalanced which would cause even more imbalance with load current between phases (think about the phase angles involved and not just the magnitudes).

The multi-grounded-neutral stray voltage problem cant really be eliminated but only transferred or distributed over a larger equipotential area with the proper ground grid system design; ie. grounding, bonding, etc.

One approach to minimize step potential is to use high resistivity crushed rocks to increase resistance between an individual and the ground (as commonly seen in substation applications).

Lastly, a 7 volt difference could be considered negligible or very serious depending on the application. Think about some unmanned remote pump station vs. a residential swimming pool. Engineering judgment would be required.


Sent from my iPhone using Tapatalk
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Let’s not forget the main benefits/reasons of connecting transformer primaries line-to-neutral instead of line-to-line... improved voltage regulation and ability to re-ground the system remotely via the transformer or transformer bank.

With line-to-line primaries, the voltage would be very unbalanced which would cause even more imbalance with load current between phases (think about the phase angles involved and not just the magnitudes).

The multi-grounded-neutral stray voltage problem cant really be eliminated but only transferred or distributed over a larger equipotential area with the proper ground grid system design; ie. grounding, bonding, etc.

One approach to minimize step potential is to use high resistivity crushed rocks to increase resistance between an individual and the ground (as commonly seen in substation applications).

Lastly, a 7 volt difference could be considered negligible or very serious depending on the application. Think about some unmanned remote pump station vs. a residential swimming pool. Engineering judgment would be required.


Sent from my iPhone using Tapatalk
Agreed.
7 volts isn’t above the 10 volt threshold.

7 volts on a fence, nothing.
7 volts in a milking barn, devastating...
 
Let’s not forget the main benefits/reasons of connecting transformer primaries line-to-neutral instead of line-to-line... improved voltage regulation and ability to re-ground the system remotely via the transformer or transformer bank.

With line-to-line primaries, the voltage would be very unbalanced which would cause even more imbalance with load current between phases (think about the phase angles involved and not just the magnitudes).




Sent from my iPhone using Tapatalk
Can you explain more why line to neutral primaries have better voltage regulation? I'm not clear on this.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Let’s not forget the main benefits/reasons of connecting transformer primaries line-to-neutral instead of line-to-line... improved voltage regulation and ability to re-ground the system remotely via the transformer or transformer bank.
Explain.

With line-to-line primaries, the voltage would be very unbalanced which would cause even more imbalance with load current between phases (think about the phase angles involved and not just the magnitudes).
Same can happen on a wye system with poor balancing. To the point utilities correct the phase to neutral voltage within 1% via voltage regulators while the line-line voltage causes problems with induction motors.

The multi-grounded-neutral stray voltage problem cant really be eliminated but only transferred or distributed over a larger equipotential area with the proper ground grid system design; ie. grounding, bonding, etc.
More money being thrown at masking a problem which can be avoided all together being cheaper in the long run in not using the MGN as a normally current carrying conductor.

One approach to minimize step potential is to use high resistivity crushed rocks to increase resistance between an individual and the ground (as commonly seen in substation applications).

Lastly, a 7 volt difference could be considered negligible or very serious depending on the application. Think about some unmanned remote pump station vs. a residential swimming pool. Engineering judgment would be required.


Sent from my iPhone using Tapatalk

Right, but not always possible to cover a whole area with crushed rock.
 

__dan

Senior Member
Give it time, revolution is inevitable in the current generation. Have you seen the news?
Not a revolution, it's an application for a competing product or method (meaning it has to come in cheaper and more reliable than the present incumbent conventional solutions).

Good discussion. I'm bidding for a different spot within and without my present arrangment. When I talk to the recruiter there's only really two things I want to express. The other is that they should just put me in a spot where they can pick my brain for patents (I am advised to leave out the part where I would do it for the $4 / hr). The discussion gave me insight into the factors of the problem, and from there, there's always 3 or 4 different ways to solve any problem. I was advised that if they pay you cheap then they think you are cheap (that's all you're worth). I could come in and do the job until they decide to start paying me, but that's what they have gates and chain link fences for.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Existing might remain where surviving, but new construction will be phase to phase.
Where surviving??
MGN is nationwide not just a passing fad.
Phase to phase is surviving because it’s cost prohibitive to switch to MGN.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Where surviving??
MGN is nationwide not just a passing fad.
Phase to phase is surviving because it’s cost prohibitive to switch to MGN.

In simple terms MGN will eventually become what ungrounded delta is today.

I know MGN is nationwide, as where Edison fuses, 2 wire NM and ungrounded receptacles.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Not a revolution, it's an application for a competing product or method (meaning it has to come in cheaper and more reliable than the present incumbent conventional solutions).

Good discussion. I'm bidding for a different spot within and without my present arrangment. When I talk to the recruiter there's only really two things I want to express. The other is that they should just put me in a spot where they can pick my brain for patents (I am advised to leave out the part where I would do it for the $4 / hr). The discussion gave me insight into the factors of the problem, and from there, there's always 3 or 4 different ways to solve any problem. I was advised that if they pay you cheap then they think you are cheap (that's all you're worth). I could come in and do the job until they decide to start paying me, but that's what they have gates and chain link fences for.
Long term effects passing current to earth, ie stray voltage and magnetic fields will be found to present cost to society which is many times greater than connecting everything phase to phase.

For example, a dairy farm with poor milk output is a blow to the local economy driving up cost for everyone including the needy due to limited local supply vs demand.

There is also the fact 3 wire distribution is almost exclusive in many developing countries where cost takes precedence in bringing power to people, power that is often stolen or unmetered.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Where surviving??
MGN is nationwide not just a passing fad.
Phase to phase is surviving because it’s cost prohibitive to switch to MGN.

Only way I can see MGN surviving indefinitely is with everything being fed by banked units like this:


1618183306224.png

Or padmounts like this:

1618183669182.png


However, it won't be long before someone in a new commercial or industrial build says, hey, can I have 416 volts instead?
 
Give it time, revolution is inevitable in the current generation. Have you seen the news?
I am not buying it, sorry. For one, I dont think stray current from MGN's are as wide spread and serious a problem, as you say. Then, how many people really understand this stuff? ITs all greek to 99.9% of the population, so I dont see a "revolution" happening, Lawmakers dont have a clue about stray current, you really think they will pass laws prohibiting MGN's?
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
I am not buying it, sorry. For one, I dont think stray current from MGN's are as wide spread and serious a problem, as you say. Then, how many people really understand this stuff? ITs all greek to 99.9% of the population, so I dont see a "revolution" happening, Lawmakers dont have a clue about stray current, you really think they will pass laws prohibiting MGN's?

So I ask how was California and rest of the world able to forbid them?
 

Hanalee

Member
Location
China, Hongkong
Occupation
Electronic Engineer
Well, I have something to add...
AC is bidirectional current. The current carrying wire is placed in rotating magnetic field, so the direction of flow of electrons also varies with the movement of the magnetic field.
 

__dan

Senior Member
Well, I have something to add...
AC is bidirectional current. The current carrying wire is placed in rotating magnetic field, so the direction of flow of electrons also varies with the movement of the magnetic field.
In the scenario where the current flows over the jumper from the Utility neutral to the fence, the question would be which one is the source and which one is the load. It's easy to assume the Utility neutral is at a higher voltage relative to the fence. But in the scientific method, both assumptions are valid (or would have to be listed as possibly true). Both would be tested, but only one would be tested and proven true.
 
Top