Interesting blog on fracking

[charles]

my copy of BS 7671 states low voltage as not exceeding 1000v ac, so 11kV is "High voltage"

[Java Jive]

Thanks for that sad substitute for reasoned debate, same to you Dumblinson ...

You forgot to mention ...

"National Grid has a statutory obligation under the Electricity Act

1989 to develop and maintain an efficient, coordinated and economical system of electricity transmission, and to facilitate competition in the supply and generation of that electricity. National Grid also has a statutory obligation to have regard to the preservation of amenity in developing the transmission system, and in doing so has to make careful and informed judgements on the relative merits of overhead lines versus underground cables.

On the grounds of reliability, capability, cost, construction impacts and land use, overhead lines are preferable to underground cables. Whilst underground cables offer benefits in terms of reduced visual impact, their installation can significantly impact upon sensitive and protected ecological and archaeological areas, as well as restrict the use of land in the long term."

The whole tenor of the document is quite clearly designed to sell us the need to put cables overhead, yet unfortunately it only gives comparative figures between overhead and underground for the surrounding magnetic fields! The cynic in me asks: "If underground cabling is no more reliable than overhead, why not give comparative figures for that as well?" So, while certainly an interesting read, I don't think it tells us anything very much other than NG would like to sell the public the need for overhead cables, which, again being cynical, we knew already, because they have rather a lot of them to sell.

Perhaps you are right that underground cables are no more reliable than overhead, but I still haven't seen anything conclusive in terms of comparative figures for reliability and maintenance costs that would settle it one way or another, and it would contradict both the quote supplied by The Other Mike, which implied that the most reliable parts of the system are those parts which are buried, and my own experience of living in both country and town at different times in my life, which is that overhead cables are more vulnerable to lightning, icing, and wind.

[The Other Mike]

The maintenance cost for a transmission overhead line are minimal. Based on existing infrastructure installed in the 60's and improvements since then It's a tower paint every 15 - 20 years, spacer replace every 25 - 30 years. Maybe a restring after 40 years with higher and /or different technology rated conductor (as has happened in the past decade or so with a number of lines)

Transmission cables are installed and it is basically a waiting game for the fault to come. It might be the day after intallation, or tomorrow or in 20 years time. The maintenance for very modern cables IS lower than overheads - this does contradict the 'published' view which is based on oil filled cables.

But the repair costs can be an order of magnitude or two higher than overhead. Cable jointing after a fault at these voltages and currents is not a case of a crimp and an epoxy pour, finished off in a couple of hours.

The key factor is for a typical 400kV cable vs overhead is upwards of 17 million quid capital spend avoided per km by going for overhead. The transmission operator is permitted to charge to a level based on their asset value so you would have thought they want to inflate it as high as they can by going for the expensive undergrounding option.

The reality is they, being the engineers, the regulator and the accountants don't want to, because they actually understand that undergrounding transmission lines is simply pissing away money.

Not at 10 x the cost for a transmission circuit you don't.

The money has to come from somewhere. Maybe you think a 500+ quid a year extra infrastructure cost on every domestic electricity bill is justified. If so then you are lined up at the top table alongside the fuckwits from FoE, Greenpeace, CPRE and RSPB among others.

The economics I admit are different at distribution voltages, but not uinexpected when privatisation meant the loss of thousands of staff across the country dedicated to fully walked line patrols and proactive tree trimming.

[The Other Mike]

There is a 400kV substation at Sundon next to the M1, it's a bulk supply point so there will be some 11kV or 33kV kit.

Conductors galloping in Canada

[The Other Mike]

Not strictly correct, they all need some method of carrying the heat away. Direct bury is used in many cases, the same as for distribution cables but with very strict controls on the excavation and backfill (lessons learnt in the UK many decades ago but later reinforced by the Auckland cable problems in the

1990's) Water cooling in troughs is used occasionally but it is often easier to increase the size of the cable and improve the backfill than use water cooling.

Oil is the insulation medium for the vast majority of UK transmission cables. There are also a few gas insulated 'cables' - a few are even well above ground level.

More recent installations such as the London extension and the Woodhead tunnel use XPLE insulation so no oil or gas.

In general active cooling is avoided in the UK

[The Other Mike]

If you are measuring it by the number of faults he is possibly correct as they are not affected by lightning strikes and transient faults do not exist.

If **transmission** voltage cable faults it is **always** a hard fault where repair and restoration takes weeks or even months, not 0.5 seconds for an auto reclose to a few days for a partial restring or insulator string repair.

An overhead line, because it is air cooled, also has significantly more overload capability, and can be loaded almost regardless of the prevailing conditions without suffering permanent damage or restricting future loading hours days months or years ahead

Overhead transmission lines are a well proven extremely reliable solution at

1/10 of the cost of an underground cable. A strange combination of an engineers and accountants choice

[The Other Mike]

Falls off chair in shock at this stunning revelation. An economist you say?

Clearly not, or at least he wasn't paying.

You *really* think that?

[tony sayer]

In article , Java Jive scribeth thus

Not strictly true. Here in Cambridge we are supplied by One main and one smaller substation/s IIRC, fed by 132 kV overhead lines the main one of the 400 kV grid at Burwell, the whole of the city is fed via underground cables.

From the main substation at Cherryhinton there are a few lines off that at 11 and 33 kV. I have never known a problem with the 132 kV lines but several with the lower 11 ones and the underground plant..

[The Natural Philosopher]

well that is not necessarily proof of your case.

1/. There are many more 33kv and 11kv things than there are 132kv things. 2/. there are no overhead 33kv and 11kv things to compare like for like with.

Certainly the experience of at least 11KV overhead things round here is that they are notoriously unreliable in open rural areas.

Corrosion, branches and lightning strikes being the three main causes of 'issues'

Conversely at above 33KV, the towers are much higher and won't suffer tree damage, and the cables are big enough to take strikes with no more usually than a brief disconnect.

In an urban situation HT cables at roof level are a UK nono anyway. They are nearly ALL buried. As are lots of other thngs that need digging up periodically.

So the situation is more complex.

As I said, when my undergrounding was done, the area engineer actually said 'no more 11KV is being put overhead'. Too many failures.

Neither have I seen any new 11KV stuff being put in overhead on greenfield towns and housing estates. Nor yet any overhead 250V/400V stuff.

Which suggest that the cost benefit of undergrounding is firmly in favour of it at 11KV and below, and firmly above it at 132KV and up. with 33KV being 'on the balance'.

Yesterday we followed the massive twin 6 conductor line of pylons from sizewell B to Ipswich.. and thought '3% of the nations electricity flows down that'

A bloke on the beach was unaware that there was a power station at sizewell at all. He thought it might be 'coal' :-)

[Java Jive]

Why should you think that someone suffering a power-cut should concern themselves about the particular cause of it? They want the power, for which they pay a standing charge, to be brought back on line as soon as possible.

And d>

[Java Jive]

But if it's a single point, there is no appreciable context, and you've just read the post before which is being answered.

That is an astonishingly inept admission to make. It translates as: "I'm too thick to read your posts!" Besides, the same argument also works, but much more so, in reverse. I work down a thread reading as much as possible in preview, because ergonomically speaking that is easier and more efficient. If I'm having to constantly launch posts and scroll down to the bottom of then, often just to read single lines added to each, then the inevitable delays in so doing make it more difficult to follow the arguments in the thread. It's like having a conversation with someone on the moon where the time-lag constantly breaks up the conversation.

Imagine how it would be if, in some religious order or other, you weren't allowed to add anything new to a conversation until you repeated the entire conversation up to that point. Meaningful communication would die. To an extent that is what happens in ngs where posts get longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer and longer 'til finally you get to the bit at the end that actually matters. I am not aware of any other form of communication where this is considered a requirement.

On the contrary, I've admitted to mistakes when I have made them, for example to Tony where I had assumed from the name of the photo that the pylon in it was in Tyndrum rather than Dalmally, where it actually turned out to be.

You shouldn't be trying to text while you're driving.

[charles]

The phrase "Power Cut" to me means a deliberate act (as happend during the miners' strike). What is more common is a "power failure" and I don't think standing charges have been around for years.

But, as an Engineer, I am interested in the reason for the fault. It gives me some indication as to how long the power might be gone. It is also worth knowing whether the fault was caused by a 3rd party.

[The Natural Philosopher]

indeed. My most famous support call :

Him: 'No one will give me answer as to how long my email will be down'

Me: 'No one knows: why did you want to know?'

Him: 'because I have a massive deadline to meet to get some legal documents to a client before his case gets thrown out of court. I can fax them or courier them, I need to know whether I should that's all'

Me: "Fax them.. I can't guarantee service by the end of this working day'

Him: "THANK YOU!"

[harryagain]

I wonder how underground/overhead cables go on in an earthquake.

[harryagain]

That's because we invented the whole idea. Most of the world uses our standard. We built a lot of their railways for them.

[harryagain]

Amazing. I wonder how long they could last in those conditions.

[harryagain]

I wonder if the trick with fluorescent tubes (lighting) works in those houses? Free leccy!

[The Natural Philosopher]

approximately as badly as overheads do.

or after a tsunami..

or after an ice storm

In short apart from actual serious earth movements. underground cables are better protected from natural disasters.

next silly question?

[harryagain]

I imagine most will be replacements. As old power stations are demolished, the power lines will go too.

[The Natural Philosopher]

A long time. often happens. what is nasty is if they touch.

That happens too.