Where Do Electrons Come From in DC Generated Current?

[nsaspook]

the physics of electricity seems unclear to even the top physicist

Richard Feyman suggests that we continue to assume that the energy flows inside the copper! ...

Listen to these comments by Richard Feyman to see the context of his statements. Without a some background in simple physics the visualization of forces moving in space due to current flow in a wire is a complex way to explain electricity to a person.

 

[nsaspook]

Personally I prefer not to think of energy as flowing, as that makes it seem like energy is something physical, which as far as I know it is not. Instead I prefer to think in terms of current, voltage, etc.

If energy is not physical then what is it? We know that energy and matter are closely related and can be converted from one to the other. Electricity isn't a source of energy, it's a transport of energy where current and voltage are properties of the transportation system. I think it's very natural to see it as a flow from one point to the next when looking at systems using electrical power for work. I do agree that flow also make you think of water flowing with all the problems that analogy brings.

 

[Drakkith]

If energy is not physical then what is it? We know that energy and matter are closely related and can be converted from one to the other. Electricity isn't a source of energy, it's a transport of energy where current and voltage are properties of the transportation system. I think it's very natural to see it as a flow from one point to the next when looking at systems using electrical power for work. I do agree that flow also make you think of water flowing with all the problems that analogy brings.

I think we can both agree that it isn't physical. You can't touch it, it exerts no force, etc. Without derailing the thread, all I'll say is that I stick to the basic definition of energy: the ability to perform work. But there are plenty of "what is energy" threads here on PF if you'd like to look at them. Just do a search.

 

[tiny-tim]

If energy is not physical then what is it? … I think it's very natural to see it as a flow from one point to the next …

I think we can both agree that it isn't physical. You can't touch it, it exerts no force, etc.

isn't this semantics?

nsaspook is basically saying that the field is physical, and that it "flows", as measured by the energy of the field

the field exerts a force, but its energy doesn't, any more than the energy of a hammer exerts a force

 

[Drakkith]

isn't this semantics?

I don't know. I'm tired and after about 5 times of attempting to unconfuse myself I have failed. And I think I've had too much ice cream.

 

[yoga face]

What do you mean by "literally grounded". If you mean the green or bare wire safety ground normally used in a home it should never have current flow or 'EMF' unless there is a fault. (short or miswiring)

http://www.allaboutcircuits.com/worksheets/ground.html

no I mean the return wireapparently there is a return wire to the power generation facility

this return wire is sometimes grounded in the sense it is no longer returning to the plant but , I presume , is literally placed in the ground I such a case would this "return" wire have A EMF FIELD AND WOULD THIS FIELD HAVE WAVES OF EMF ENERGY THAT WOULD SHOCK YOU or would the energy waves have been used up creating thermal energy (light and heat) in the resistance ?

 

[nsaspook]

no I mean the return wire


apparently there is a return wire to the power generation facility

this return wire is sometimes grounded in the sense it is no longer returning to the plant but , I presume , is literally placed in the ground


I such a case would this "return" wire have A EMF FIELD AND WOULD THIS FIELD HAVE WAVES OF EMF ENERGY THAT WOULD SHOCK YOU or would the energy waves have been used up creating thermal energy (light and heat) in the resistance ?

A 'single' wire utility feed with a ground return is used today in some cases but it's not normally used in a (US based) local utility. It's a option in some HVDC long distance systems.
http://en.wikipedia.org/wiki/Single-wire_earth_return#Use_for_HVDC_systems

http://en.wikipedia.org/wiki/Pacific_DC_Intertie
I think it normally runs in bipolar (two wire) but ground return is possible.

The Pacific Intertie consists of:[3]

The Celilo Converter Station which converts three phase 60 Hz AC at 235 to 525 kV to ±500 kV DC at 45°35′39″N 121°6′51″WCoordinates: 45°35′39″N 121°6′51″W.
The grounding system at Celilo consists of 1,067 cast iron anodes buried in a two foot trench of petroleum coke, which behaves as an electrode, arranged in a ring of 3,255 m (2.02 mi) circumference at Rice Flats (near Rice, Oregon), which is 10.6 km (6.6 mi) SSE of Celilo. It is connected to the converter station by two aerial 644 mm2 steel-reinforced aluminum (ACSR) cables, which end at a strainer situated at 45.497586°N 121.064620°W.
A 1,362-kilometre (846 mi) overhead transmission line consisting of two uninsulated conductors each 1,171 mm2 in cross sectional area, containing a steel wire core for strength.
The Sylmar Converter Station (34°18′39″N 118°29′21″W) which converts DC to AC (a process also called inverting) and phase-synchronized with the L.A. power grid.
The Sylmar grounding system is a line of 24 silicon-iron alloy electrodes submerged in the Pacific Ocean at Will Rogers State Beach[4] suspended in concrete enclosures about one meter above the ocean floor. The grounding array, which is 48 km (30 mi) from the converter station and is connected by a pair of 644 mm2 aluminum conductors, which are in the sections north of Kenter Canyon Terminal Tower at 34°04′04.99″N 118°29′18.5″W installed instead of the ground conductors on the pylons. It runs from Kenter Canyon Terminal Tower, via DWP Receiving Station U, Southern California Edison Northridge Substation and Rinaldi Electrical Substation to Sylmar Converter Station. On the section between Northridge substation and Rinaldi Street substation one of the two ground conductors of 2 parallel running 220 kV powerlines is used as electrode line conductor.
The combined wires have a capacity of 3.1 gigawatts in bipolar mode.

The field generated from the ground return current would be very near and concentrated between the overhead transmission wire and it's unlikely any harmful ground potential could be measured on a man sized object.

 

[Bearone]

Here's a link many readers may find interesting.
Zoom in and one will see the differences.

https://www.google.com/maps/@45.4976136,-121.0645765,97m/data=!3m1!1e3

It's a link to view from satellite, the Rice Flats Electrode.
Notice the tower in the "center" of the circumference, has four conductors to the NW toward Celilo, two for the DC poles and two for the DC GND or reference to earth, when both poles are used. The remaining two conductors to the South are the poles to Sylmar, CA.
Earth return from Sylmar is via overhead to the Kenter Canyon Terminal Tower, then out to and just above the ocean floor from Will Rogers State Beach.
I believe the GND reference to Earth for both poles is connected when both poles are in operation. However, from one pole (+) or the other (-) during GND Earth return with monopole operations, only one pole, the (+) or (-) pole is connected to GND (earth) return to complete the current path.
This method of return has not been used over the years due to electrolysis issues.
This center point of this special tower, is the center point of the radials to the outside ring circumference (2.02 mi) which has the petroleum coke, along with the conductors, radials embedded within the trench.
Today's satellite view, show no traces of the original trenches or outside circumference ring. It's been over 45 years since the electrode was constructed.
I believe BPA is doing work in this area around 2012 or later, perhaps this project has been completed as of the time of my post?
I read at another web site, one person said' "all I saw was a tower and no marks of the radials or outer ring. I wonder why?

 

[davenn]

I, likewise see no hint of buried ground radials, I only see 2 towers and heavily cultivated farmland

Every tower will have an earthmat anyway for grounding lightning strikes etc

none of this has anything to do with single conductor, Earth return systems as was being discussed

Dave

 

[sophiecentaur]

In some commercial power systems, the return [negative] path is earth...in others it is ground wires..in either case the electric potential moves electrons along a CLOSED circuit..a continuous path.

1. Could you quote a modern day example of that?
2. Could you quote a modern day example of DC transmission of power, direct to the user?
Even if you can, it is such an unusual situation that it hardly constitutes a useful answer to the OP's question. Some signals are sent 'one legged' but that is a different issue. Earth return is possible but just not a good idea.
[Edit: I stand corrected about the single-legged power distribution. It's not a practice in the UK but I see they have used it in Australia. For high voltage distribution, it must require a very extensive Earth mat at the sending and receiving terminals to avoid a significant voltage gradient along the ground locally (?). There is an obvious advantage in cost savings, of course, particularly over very long runs - which would be the ones needing high voltage operation.]

 

[2milehi]

When I first heard of DC transmission lines I wonder if Edison's spirit when to Tesla's spirit and said with a smirk on his face "I told you so!".

 

[sophiecentaur]

When I first heard of DC transmission lines I wonder if Edison's spirit when to Tesla's spirit and said with a smirk on his face "I told you so!".

Engineers, worth their salt, all appreciate that circumstances alter cases. It's only when commercial interests come into it that they tend to wear blinkers.

 

[anorlunda]

Edison was right, but only if you accept his vision of the power utility company. Edison envisioned one illuminating company for each 2-4 city blocks.

When someone proposed to send power long distances from Niagara Falls, Edison agreed that the long distance transmission must be AC.

The AC/DC debate in popular history was really more a debate about business models. Edison wanted to sell illumination, not power. Edison attacked AC as a dirty politics tactic. Among engineers there was never much doubt about the advantages of both AC and DC in different circumstances.

Con Ed in New York City continued offering DC service to consumers until the 1980s.