When there are high levels of third (and higher multiples of three) harmonics in the current waveform there can be a high current flowing in the neutral conductor even when the phases are equally loaded. This is a serious problem with some types of load. John
The main wires on big pylons are always multiples of three, and are simply load carrying duplicates. The wire that runs across the top is much smaller, un insulated, and is a neutral/earth that carries just any residual imbalances between phases
A typical UK main backbone pylon will carry *six* insulators each carrying four conductors to provide a *mechanically * balanced setup and a *single* earth/neutral wire running along the pylon tops.
Thus using standard wire sizes and presenting a symmetrical load to the pylon.
It also acts as a lightning protector for the power cables.
Not so as I have noticed...I once saw a strike zigzagging between the main power cables that didn't go near the earth at all
I know that its supposed to do that, but lightning is amazingly tricky stuff.
But not as many and they are much the same layout as the other HV lines.
And there are 33kv and 11kv networks
The three phase 11kv that runs past my house and powers my substation, has no neutral or earth
This is typical round here, where it's not undergrounded..
Have something to add? Share your thoughts — no account required.
Ask the community — no account required