205 comments on Will the US Electric Grid Be Our Undoing?
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205 comments on Will the US Electric Grid Be Our Undoing?
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GAIA Host Collective
The "ridiculous dangling wires" are there for a reason. The cost to cable the circuits underground is 10x the cost of overhead. Plus, there is higher ampacity for the same size conductor for aerial over cable. Think people complain about higher electricity costs now, wait until they see the bill for buried cable systems!
I won't go into the differences for maintenance and repair between the two...
The environmental impact of ALL that trenching for underground cables !
Alan
Why not?
The dangling wires are an expedient. 'It's cheaper' is the rationalization given for all that is done in this country, even if it's not and even if there are other benefits to 'more expensive'. Lowest cost is not always best value.
Problems with dangling wires:
- Weather and debris vulnerability. Underground utilities are far more robust.
- Ugly. One of the depressing features of the auto slum- scape is the endless mess of ridiculous dangling wires, not to mention all the other power infrastructures added to them; the poles and towers, transformers, grounding, switching, lamps, meters, etc. This is a significant issue; why do we build anything in the first place? Do we exist in order to please the infrastructure? Or, does it exist to serve us? Do we not build for pleasure and utility or is all a part of the rat race? Is our life- support system an end ... to support of the cost side of a business ledger? At bottom, who cares whether a utility makes money or not; the issue is value to the user which is the community the utility pledges to support. If a business cannot serve the customers except by expedients it will fail.
- The 'eyesore' issue is a reason large transmission lines cannot be sited. Nobody wants to look at them; they destroy the landscape. Adding capacity to the grid does and will continue to involve long passages through the courts as adding capacity is always sued by persons and entities adjacent to it. Capacity is ugly. Ugly is an externality that cannot be ignored - like all the other externalities - by the utilities. NIMBY is powerful and load- shedding always takes place in 'undesireable' neighborhoods whoee inhabitants cannot afford lawyers. Putting capacity underground solves the problem. Putting distribution under the streets is simple because the streets already go everywhere ...
- Dangerous. Power lines fall on people while energized and kill them. Underground utilities do not do so, although poorly maintained installations can cause fires and explosions. Nevertheless, the same sorts of maintainence failures take place in the dangling wire universe and the fires and explosions take place in open air. (I used to live in a building that was badly damaged by a transformer explosion.)
- Not only is our electric infrastructure a great eyesore, it is an unnecessary eyesore. In most cities, the electric distribution is currently underground. Almost everywhere in the US, the water, sewer, natural gas, telephone, subsciption television and communication/internet systems are also underground. Even where electric is overhead, cable TV and telephone are placed underground because such an istallation is less vulnerable to weather and connections can be made and service performed without the need for a large, six- wheel bucket truck. As for installation; the companies that provide broadband internet are currently installing tens of thousands of miles of fiber 0ptic duct underground and have been doing so nationwide for the past fifteen years. What is easy for the fiber optic people should be no less easy for the power companies. Other utilities have the same universal service requirements and safety concerns as does the electric utilitiy.
If the gas company can provide universal service underground, with large pipes, valves, meters, ducts and other equipment, and do so on a cost effective basis, so can the electric utility.
Putting the wires underground is a job that needs to be done, It is obvious and the requirement increases with every long blackout caused by a storm. To put in a depression tens or hundreds of thousands of otherwise unemployed men to work at good jobs with good pay; the wires of America can be buried at a small cost to a government that has spent already trillions on air. It would be an investment with a return of agreeability, safety and permanence.
Underground residential distribution is one thing; putting 115kV, 230kV, or higher voltages underground is substantially different. What I reference below is referring to the bulk power system.
Yes, we do this in some cases. Aesthetics for one, inability to traverse population dense areas, two, or underwater, three. But these are always short distances, because currently the installation cost is at least fifteen times as much as overhead.
Fifteen times. We could reduce this substantially, I'm sure, with scale, but that's a lot to overcome.
Once we start getting into higher voltages we run into capacitive reactance problems that over long distances would cost more in external equipment to manage, not to mention much higher losses.
Cable faults are almost always destructive, resulting in far longer and more expensive outages. Fault location is much more difficult, as is splicing. Granted, they do occur much, much less often as you indicate...but over the long run, with more underground, this becomes a bigger issue. 85% of all overhead transmission faults can be cleared instantaneously and reclosed within cycles, resulting in a much improved reliabilty margin. Cable faults are never reclosed.
As for the eyesore issue, I tend to agree. Personally, I think the way around this, and perhaps to also employ a few more people, would be to eliminate the lattice towers and replace them with monopole structures, something not widely available 40 years back. They take up less land and in my opinion are sleeker and better looking. But lattice towers are probably only a third to a fifth (my estimate) the way through their life cycles; they are extremely robust. This would be exceedingly difficult to justify.
Cable faults are triggered in the distribution (from substation downstream) and spread upstream. A falling branch or a lightning strike will trigger one. So ... addressing the distribution would be more cost effective than not.
Why would cable faults underground be any more difficult to clear than cable faults overhead? Any duct system that could carry the conductor(s) could also carry monitoring equipment. In general high- tension is low maintainence, all else being equal - leavng out the vulnerability of downstream distribution. If an interrupting fault is a 25 year event on any circuit, enough redundant/spare capacity can be engineered into the system to prevent a ciruit shutdown, even if repair might be more costly than an overhead repair.
I don't think that an electrical trunk should be less of an investment than a transport corridor (rail line) or major highway or navigation canal. All serve an equal purpose and have the same requirement to conform to an overall value system that includes more than just cost, and maintainence ease. A high tension corridor isn't free; only by applying to the current economic status of a potential corridor a value of 'zero' - which, ironically a transmission route gains after the towers and conductors are in place - does the status quo have an overwhelming value advantage.
As a strip mine is less costly than alternatives, the expansion of more and more strip mines calls into question the value of mines and compares that value against the utility having them at all. The same value/utility measurement applies to transmission and transport corridors. The issue becomes, 'when do we have enough mines?' 'When do we have enough highways?' When is enough? The answer is not never ... 'development' or 'progress revulsion' is real even if it cannot be quantified or modelled.
Even where 'development' is taken for granted along with progress and an adman's idea of 'status' and wealth, the idea that more (and more and more) of the same is really a benefit is being re- examined. If the end product is for all to be submerged into a kind of industrial process, the 'sex appeal' of development disappears. It may be happening already.
I don't know if 'slowing development under current crisis conditions' is in the general best interest, but overall value has been ignored for too long and the reputation of development in general - which is always given a positive cost- benefit ratio - is very poor.
"Why would cable faults underground be any more difficult to clear than cable faults overhead?"
Overhead lines are uninsulated (bare metal). They rely on the air gap between the wire and ground, plus ceramic insulators on the towers, for insulation. Sometimes they flash over to ground for some reason. When the relays shut down power, the electric arc de-energizes and insulation integrity is restored. The relay can reclose and restore transmission within a few cycles. Generally the faults are self-repairing.
Underground cables rely on a layer of oil impregnated paper or some kind of plastic sheething (depending on cable design) to insulate from ground. When they fault, they fault permanently. Someone has to go out and dig up and splice the cable. Underground insulation is probably ok up to 100kVAC. Above that and it gets very expensive. Overhead lines are more vulnerable to bird poop, fires, dust storms, gunshots, tree limbs and other problems, but at transmission voltages (above 100kVAC) its pretty easy to repair the problem. Often fixing the problem amounts to waiting from a few cycles to a few hours. Cables above 100kVAC are really, but really expensive. There is no comparison to fiber optic cables.
Jeff Barton
Jeff is spot on.
An aspect he hasn't pointed out is heat. In overhead insulate wires the heat is dissipated away in the air. Underground cables have a much bigger problem in this. The city of New York has a lot of experience with this. They have found it necessary to put electrical cables inside underground corridors large enough to permit workmen to stand upright in them to allow for enough space for heat dispersion and repairs.
It would be a lot more complicated than just throwing a cable into the ground like we do with fiber-optic.
Tailwinds! ChipSeal
Siemens offers three rigid, hollow copper pipes suspended in a SF6 gas.
Not cheap, but it has advantages for short distances.
Alan
SF6 is really an excellent green house gas.
Unfortunately, one of the worst !
Alan
You're missing the point. It doesn't matter whether the air- insulation is more cost effective or whether the need for grid power is utmost, the greatest obstacle to increasing capacity is public opposition to generating plants, towers and transmission lines.
Public opposition isn't going to go away, in fact it is likely to become more intense. Accomodating it will cost more money and the utilities will find themselves in a position where the difference in costs between various options will be negligible and public relations will tilt the balance.
Ten years in court with multiple appeals add a lot of percentage points to the cost of a transmission line. If the court rules against the utility and the ruling is upheld on appeal ... no transmission line at all.
I tend to agree all around, especially with transmission line structures being an eyesore. I am constantly on the look out for better aesthetics for power lines and substations. So I agree with Steve from Virginia and the collective engineers. Just because it was done one way in the past doesn't mean its the only way to do things.
I won't repeat what has been said about the differences in repair except to add that underground repair work requires at least a three man crew and can take hours to set up for enclosed space entry. An overhead line can be repaired by one lineman.
A little more about clearing times. It depends on the protection and control system. If a transmission line has an automatic reclose, the duration is around 30 cycles or 1/2 second. The duration is decreased as the voltage increases for stability reasons. As noted earlier, cable faults are mostly catastrophic and don't have a reclose. When a cable trips off, its down for the count and fault detection has to be employed (typically >4 hours, less if they get lucky).
There is no dispute about putting the cables in the ground for distribution systems. Its been relatively equal in cost to do over the past ~50 years as subdivisions were being built and the cable plant went in with the other underground infrastructure.
Transmission on the other hand...
I've just finished the initial design for a 138 kV transmission system that is using overhead and power cable. Most cable installations these days up to 230 kV are going with XLPE (Cross Linked Polyethylene - or plastic) insulation. Above 230 kV assessments have to be made for efficiency and life span. We are keeping the footprint of the overhead lines to a minimum using a single mast wood structure, and the power cable is going under a provincial park via a directional bore of world benchmark setting proportions.
We have to find ways to make it work for all parties. You see, my initial proposal was to do a cut and fill power cable installation through the park - just as one would do in a city. This park is remote and not easily accessed, but with this development we could provide that access. The cable installation would be designed so that once complete it would look like a trail system through the park complete with sleeping and picnic shelters over the vault manholes. Within 2 to 3 years, no one would even know there was a power cable installation underground. (BTW, I'm using differential protection throughout with fast clearing times of 3 to 5 cycles and reclosing on the overhead line). The power cable installation is over $15 million in itself, so we are protecting the h-e-double-hockey-sticks out it.
If the project goes ahead, it may get some attention during the Vancouver 2010 Winter Olympics as the project is in the vicinity.
To put a reality spin on it, we are stuck with the existing overhead transmission infrastructure. It isn't going anywhere for quite a while.