'27
The resistance in earth is interesting.
Here's another way of thinking about it.
A village of people, let's say 100, live beside a water source that they use for cooking, sanitation, crops and livestock. The Rural Electrification Assoc. (REA) comes along and offers them 1 Amp at 19.1 kV. The REA substation is 50 miles away as measured down the S.W.E.R. right of way. A single strand of #4 aluminum conductor - steel reinforced (ACSR) is installed to the village.
Everyone decides that a water pump will be powered by electricity, greatly reducing the time spent hauling water, and making it practical to do some irrigation. A 10 HP pump is installed along with a few street lights. The village draws 0.5 Amp @ 19.1 kV with everything running, or 9.55 kW.
One of my references shows #4 ACSR has 0.415 Ohms per 1000 ft. 50 miles of #4 ACSR will have 109.6 Ohms in it!
The voltage drop on the #4 ACSR from substation to village will be 54.8 Volts, but out of 19,100 Volts, that's nothing.
Let's say that the village transformer ground has 25 Ohms resistance to earth. The village portion of the earth return will have a voltage drop of 12.5 Volts.
The substation ground grid will also have a voltage drop as will both transformer impedances, but at 0.5 Amp, they are also small.
The sum of all the voltage drops around the S.W.E.R. circuit won't exceed 100 Volts (which, at 0.5 Amp, is a 50 Watt loss).
Remember, the Earth, (after the contact resistance) is simultaneously an infinite source and a sink of electrons.
