Hi Elektroinstalacje, and welcome to the forum.
There are many different voltage levels used throughout the U.S., more than in most countries due to the sheer size of the nation and the various electricity companies there.
Even at the low-voltage end of the scale there are several different systems: 120/240V 3-wire, 120/208V 3-phase, 277/480V 3-phase, 240V delta, etc.
I remember somebody posted a link to a document from Cooper Transformers a year or two ago which provided a pretty good explanation of some of the different HV systems in use. Can anyone remember the link?
Over here in Britain, our most common voltage levels are 240V 1-ph or 240/415V 3-phase, 11kV, 33kV, 66kV, 132kV, 275kV, and 400kV. There are still a few local distribution systems using 6.6kV, but these are quite rare now. There are other levels used for specific purposes, such as a high-voltage D.C. interconnection with France, 25kV A.C. for long-distance railways, etc.
Here are a few photos:
Typical 33kV line Typical 11kV line More 11kV local distribution Overhead to underground transition with switch, also 11kV Small pole xfmr on single-phase spur line Typical 3-phase pole transformer Same pole, showing secondary fuses Typical pad-mount xfmr in wooden enclosure All above transformers are 11kV primary, 240V or 240/415V secondary.
Typical 240/415V overhead distribution lines (Poles in that last photo also have telephone lines lower down.)
Single-phase xfmr feeding 240/480V 3-wire distribution in rural area All of the above are my own pics. Feel free to copy and use if you wish.
For the larger transmission lines (132kV and upward), have a look at some of the photos on this site:
http://users.tinyonline.co.uk/bigh/bigh/photoarchive.htm