Return current through General Mass of Earth
Return current through General Mass of Earth
(OP)
Hi,
I have in mind this question for years,now I got this forum to ask this question.
When we model a simple earthing system as in attached PDF,we assume Earth current return to source even when source earth is kilometers away.
I understand whatever the current go to earth through earth electrode,it get dissipated as heat and finishes it journey in nearest earth electrode.If this is true how earth current return back to source in models.
If a transient fault like Lightining happen,I can think of such a flow of current.But why in normal faults,how we
assume current goes through general mass of earth??
I have in mind this question for years,now I got this forum to ask this question.
When we model a simple earthing system as in attached PDF,we assume Earth current return to source even when source earth is kilometers away.
I understand whatever the current go to earth through earth electrode,it get dissipated as heat and finishes it journey in nearest earth electrode.If this is true how earth current return back to source in models.
If a transient fault like Lightining happen,I can think of such a flow of current.But why in normal faults,how we
assume current goes through general mass of earth??






RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
That is, a long distance DC high volt line needs to be point-to-point transmission
(AC generator -> ac-ac transformer -> ac-to-dc converter-> dc long distance line-> dc-to-ac converter, ac-ac transformer),
and not a source by itself of a DC-supplied network with many dc-ac conversion stations along the dc route. True?
RE: Return current through General Mass of Earth
Soil has a good deal of impedance between one clod and another. But given there are millions of clods, it tends to act like a very low impedance path. If the local soil is, say rock or sand, you will find it difficult to make contact with enough clods to get a good connection at the ground rod. If there just happens to be a pipeline, or rail road in the area, you could find they can conduct a significent amount of current, which the owners of said pipeline don't like.
RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
If you mean the use of earth for a return path, this has been in use almost since the beginning of HVDC systems back in the 60's.
RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
The problem with high voltage dc with earth return is in the grounding. Or getting enough ground contact to accept the current. The current will tend to dryout the local ground grid soil, at which point the grid resistance will increase. There are things you can do to increase the ground contact, like use charcoal, or some high metal supliment for the soil, but it is the same thing as increasing the ground grid size (I think it is cheeper than increasing the ground grid).
RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
https://www.denali.gov/dcpdb/Data/attachments/Pola...
RE: Return current through General Mass of Earth
The Northern Ground Terminal is at Rice Flats a few miles south of Celilo directly under the line. It is a 1700 foot radius circle of #4/0 awg copper connecting 1,067 cast iron anodes each 18" diameter x 60"long. Total wire is 10670 feet. Anodes and wire are buried 6 feet deep and surrounded with a 2'x2' bed of carbon coke. Three 1700' +/- long "spokes" of 1000MCM copper connect the circle to DC Intertie tower 8/1 that is in the center of the grid.
GE did testing on the ground system prior to system energization. "Telluric currents were noted, as was cathodic protection where it was present. 300 amps of current were circulated in the earth between the ground electrode at Rice Flats and the ocean electrode in Santa Monica Bay. It was assumed that the effect of 1800 amps could be extrapolated linearly from these results. ... With the location chosen, it was anticipated that there would be no insurmountable problem with the existing pipelines and other metallic structures in the ground."
I wonder if the anodes are still there 40 years later. I don't know if the line ever had to operate single pole with ground return.
RE: Return current through General Mass of Earth
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 at a strainer situated at 45.4975865°N 121.0646206°W.
The Sylmar grounding system is a line of 24 silicon-iron alloy electrodes submerged in the Pacific Ocean suspended in concrete enclosures about one meter above the ocean floor. The grounding array is 48 km (30 mi) from the converter station and is connected by a pair of 644 mm2 aluminum cables.
RE: Return current through General Mass of Earth
RE: Return current through General Mass of Earth
complex subject .To know it further,I need to go through Carsons
equations and experince on how this is acheived in different parts
of world
RE: Return current through General Mass of Earth
http://en.wikipedia.org/wiki/Single-wire_earth_ret...
Regards,
Lyle
RE: Return current through General Mass of Earth