Overhead electric cables

[SparkyTris]

On the large lattice pylons, there are as a rule, 7 cables: 3 hanging off on arms on each side, and one running across the top of the pylons.
What does each cable do? what voltage do these lines carry?
these big pylons have long ceramic/glass insulators keeping (I suppose) the lines isolated from the pylon, but they also take the weight of the cable. What is the load-bearer in these insulators? I cannot imagine they are pure ceramic, as this wouldn't be strong enough - but then, if the load-bearer was metal, the insulation would not be so good... ???

The smaller wooden poles (11KV lines?) usually carry only 3 wires. what is on each of these?

 

[ChrisRogers]

on large power lines you have 2 sets of each phase, so you have two red phase, two yellow phase and two blue phase. the 7th wire is an earth wire strung abouve them to try and deter lighting from striking the lines.
11kV lines are all 3 phase or 2 phase. neutrals are provided from the transformers at substations for 230v distribution.

 

[dw3101]

they carry three phases, they dont carry a neutral..some pylons have two circuits.. top one is earth.. some only have one side connected..

The insulators have (or had lead in the centre) on the last one I saw..

 

[Paul_C]

what voltage do these lines carry?

The three main voltage levels for long-distance transmission in Britain are 132kV, 275kV, and 400kV. There are also more limited stretches of 66kV lines.

The smaller wooden poles (11KV lines?) usually carry only 3 wires. what is on each of these?

As stated already, the cables are simply the three phases and the primary of the ste-down transformers are wired in delta configuration (no neutral).

11kV is the most common for local distribution, but a few areas still have some older 6.6kV networks. Wooden poles are also used for 33kV feeders bringing power into an area. It's easy to identify these from the much taller insulators.

Note that these are line voltages, i.e. the voltage between two phases. The voltage from any phase to earth is the line voltage divided by SQRT(3).

Outside the U.K., many other different distribution and transmission voltages are in use. In many countries it's also quite normal to find wye distribution systems (4-wire, 3 phases plus neutral) and single-phase spurs consisting of one phase plus neutral.