Re:Utility poles
by phasetransition on Wednesday February 14, 2018 @07:16PM
(#16380856)
FYI, this is the correct description of the vast domestic power in the US, which is a single phase of distribution on the primary side to a center tapped secondary transformer.
"For single phase home customers, you run a single one of those phases along a street and attach center tapped transformers to it."
True but there are a few variations. And you also have to remember that each of those single-phase lines runs back (at some point to a three phase transformer. One very important facet of creating the single-phase spurs is to make sure the load is reasonably balanced.
Three phase 240 VAC is also cheaply converted to 120 VAC single phase in the same transformer by putting a center-tap into one side of the transformer's delta-connected coils. You will get 120 VAC from that center tap to either of the adjacent hot connections but you'd better not connect anything between the center-tap and the opposite hot connection!
Re:Utility poles
by junkcollector on Thursday February 15, 2018 @11:40AM
(#16385376)
Going to be a bit pedantic here but you absolutely can have 0 Voltage. Voltage is the potential energy created by a difference in charge between 2 points. If you have a mass with sufficient free mobile charge, when you inject additional charge into it, it will rearrange the charge within itself to cancel out in injected charge resulting in 0 Volts of potential. This is the principal that a ground connection works on and why you don't have voltage inside of metal conductors, just on the surface.
If you have any conductive bar or wire of sufficient size you can safely touch both ends (and measure zero volts across them. If you stretch those conductors over miles and miles of distance, it gets harder to reference the end to both grounds at the same time. And getting a good ground can be hard. There are numerous stories of "stray voltage" making cattle jumpy, etc.
Of course if you coil up that conductor and pass a magnet by it you're going to get shocked ;)
No, that's not correct.
Three transformers is for changing 3 phase medium power, to 3 phase regular voltage (for commercial customers).
For single phase home customers, you run a single one of those phases along a street and attach center tapped transformers to it.
The center tap means from the top to the center is 120v, and from the center to the bottom is another 120v. This gives something called "split phase", and is how homes in the US are wired.
This allows you to get 240v in the house if you need it by attaching to the top and bottom of the transformer.
The center tap of the transformer is also attached to the ground, and to the neutral power line (back to the generator). This gives what is called "zero voltage" (voltage is always relative, there is no such thing as absolute zero voltage - so you just have to pick something, and call it zero).