My textbook, Practical Electronics for Inventors, Fourth Edition, by Scherz and Monk, says the following in section 2.3.1 The Mechanisms of Voltage:
In regard to potential energies of free electrons within the conductors leading to and from the battery, we assume all electrons within the same conductor have the same potential energy. This assumes that there is no voltage difference between points in the same conductor. For example, if you take a voltmeter and place it between any two points of a single conductor, it will measure 0 V. (See Fig. 2.8.) For practical purposes, we accept this as true. However, in reality it isn't. There is a slight voltage drop through a conductor, and if we had a voltmeter that was extremely accurate we might measure a voltage drop of 0.00001 V or so, depending on the length of the conductor, current flow, and conductor material type. This is attributed to internal resistance within conductors - a topic we'll cover in a moment.
I can't help but wonder if the authors are understating the potential for voltage drop through a conductor. Their estimation of a 0.00001 V drop seems reasonable for a relatively small electrical circuit, but what about for large-scale power systems, where the conductor may span many miles (say, an undersea cable, an electrical grid (although, I assume that electrical grids have hardware in place to "boost" the voltage between power plants and delivery destinations), a solar farm in the desert, etc.)? In my, perhaps naive, mind, I wonder if the voltage drop would not just be minor in such situations, but significant enough to cause practical problems?
I would appreciate clarification on this. Thank you.