Overhead power cables.

[Dave Plowman (News)]

Just how many time to these have to be replaced in a storm before they get the message that they'd survive a storm if underground?

[tabbypurr]

they already know

[Jethro_uk]

Remember how the energy companies whined like girls when threatened with a windfall tax, that it would "prevent investment"* ?

Well, the money that wasn't taken in tax went to the shareholders and directors, thus preventing the investment required for *expensive* buried cables.

If anything was going to be done by now, then it would have. (See also, "housing crisis").

*With not one journalist pointing out that tax is paid *after* investment, not before.

[newshound]

+1

[Andrew Gabriel]

Probably a lot. Undergrounding cables is much more expensive than stringing overhead. Normally only done where there's a legal requirement, or someone else pays them to do so.

[The Natural Philosopher]

It depends. When I had my supply undergrounded in order to be able to rebuild a 2 storey house, the received wisodm was that they were happy to do it as the general policy was to underground as much 11kv as they could.

The problem being theres a lot of it, its no higher than the trees by and large, so it gets a lot of stick from lightning and from tree branches falling.

33Kv and upwards I think they are less keen. And big 132/275kv pylons are so far above tree level as to be uneconomic to underground.

[alan_m]

And how many times do they have to be replaced when a JCB digs them up before they get the message that they survive road/building work if kept above ground where they can be seen?

[Dave Liquorice]

How unreliable do you think overhead is? Our supply is overhead from the grid substation at Penrith (for the 33k V feed to the local primary substation), 30 odd miles away. The back up 11 kV which runs more or less parrallel with the 33 kV is derived at the Great Selkeld primary (it's 33 Kv also coming overhead from Penrith). Both of these feeds pass over Hartside at 2,000' and a few miles south of Great Dunn Fell which recorded that 100 mph gust the other day (nothing that unusual TBH, Great Dunn Fell is one of the windiest, if not the windiest, place in the UK).

We used to get about one auto recloser trip a year, ie a couple of seconds off when a branch (or WHY) touches the line, gets vapourised, trips the auto recloser, that resets after a second or two. They seem to have upped the tree cutting frequency in the last 5 years or so and recloser trips are now less than one/year.

The longest outage we have had in nearly 20 years was after an ice storm. That brought down quite a few sections of line and the recoil snapped about 1/2 a dozen poles. Some of which supported an air switch and line join/split. Took 'em 36 hours to plant the new poles, insall air switch and re string. Overhead telephone lines (Dropwire No.10) where encased in ice the best part of 2" in diameter, stretched amazingly and recovered.

Of the other outages measured in a few hours, most have been plant failures, transformer fire and a failed insulator, spring to mind. Talking to others who live in towns, with underground supplies, some have far more power problems than we do.

[The Natural Philosopher]

In my case only once in 17 years and that was because an HGV drove over the verge and punched a stone through the armour

All in all at the rural 11KV level accidents are far less frequent on undergrounded cables

They are arguably far less dangerous too in a packed urban environment

I cant remember seeing an overhead 11KV in a major town

[The Natural Philosopher]

I'd say your experience is remarkably similar to mine

Used to be 2-3 a year, now down to less than one

[The Other Mike]

For the mobile crane driver that drove along the access road towards Hartlepool Power Station, with the jib unlatched it can be safely assumed that he will notice the overhead lines operating at 275kV the next time. The sound of a dozen or so tyres exploding and craters being instantly formed in the road surface while he shat himself in the cab will remind him too.

[Terry Casey]

I recall a power cut because of a major fault on the grid crossing the Bristol Channel during extreme weather conditions many years ago.

The cables iced up with the ice forming mainly on the underside of the cables. The increased wind resistance made it easy for the wind to swing the cables sideways whereupon the aerofoil shape created by the ice enabled the wind to lift the cables.

I remember seeing film shot from the pylons at each end and all of the cables thrashing wildly about and coming into physical contact with each other.

[newshound]

:-)

[newshound]

For me, one of the amusing things about Hartlepool PS is the unique "airlock" double gates arrangement for all vehicle access to site. Does that say something about the perceived reliability of the local population? These days of course most sensitive places have a gate plus lifting barrier, and "chicane" access too, but back when it was first built it gave the sensation of large American prisons.

[Vir Campestris]

We had 8 in 4 hours the other day. Only for a few seconds, but it still reset all the clocks :(

Andy

[Dave Liquorice]

Big branch that didn't get vapourised enough on first contact to not make a second and not making contact frequently enough to lock the auto-recloser out. I think the auto-reclosure in our line requires 3 trips within a minute before it locks out. ie on-off-on-off-on-off-lockout.

If it had been mostly off with a few on seconds on, that would be the DNO engineers trying to locate the fault by measuring ground potentials/currents when they reconnect the supply and before it trips again due to the fault. They'd almost located the faulty insulator when we rang the DNO to say each time the power was restored an insulator at the top of our pole arced over. This was after a the best part of dozen short duration power restorations.