Are "access ports" in Australia the same things that we call "manhole covers" here in the USA -- round steel plates about a meter in diameter?
Where are equipment enclosures (transformers and switchgear) located? Are they also underground?
"T > I've also read reports that indicate trouble shooting and repairing > underground power lines near the end of their life is very expensive.
Troubleshooting and repairing any kind of underground cables -- power, telco, or CATV -- is expensive at any point during the life of the cables. Physical damage due to excavation work can occur at any time.
To the extent that repair work is required near the end of life, it's usually caused by failure of the > As to burying power lines, obviously individual lines to houses and > lines to a block of houses can be buried. But is there a limit to the > amount of voltage on a line that can economically be placed > underground?
Depends on what you mean by "economical." There's no inherent "limit" imposed by voltage, but there's certainly a tradeoff between voltage and cost. Given enough money, you could probably put anything underground. As Will Roberts noted in TD 28:69, a 345-kv line exists in Boston. By my calculation, that line cost about $12 million/mile. But even that cost was (presumably) economical when compared to the cost (both in dollars and PR issues) of building it overhead.
An even bigger problem is conductor heating. For any given power, current is the inverse of voltage, and the resulting I-squared-R loss produces heat. That heat must be dissipated through insulation. If the insulation does not dissipate it safely, the insulation will fail.
The best insulation provides high electrical resistance and low thermal resistance -- in other words, air. Which is why almost all overhead power conductors are uninsulated -- just bare metal swinging in the breeze. Only customer drops (typically between 115 and 460 volts) are insulated.
For obvious reasons, underground cables have to be insulated with something else. There are two ways to control I-squared-R heating: by reducing current (increasing voltage) or by reducing resistance (using larger conductors). Both ways are employed, but larger conductors are more obvious: take a look at a primary riser, and you'll see an abrupt transition between the relatively small uninsulated conductors and the much larger conductors sticking out of the insulation at the top of the riser.
A lot depends on the costs of right-of-way acquisition and restoration requirements.
Construction in a new residential neighborhood (before lots are developed) is relatively inexpensive: the power company digs a trench, dumps in a "sand bed" (4"-6" of sand), all three companies (power, telco, and CATV), lay their cables, power puts in another layer of sand, then backfills the trench with the spoil and compacts it. Except for backfill, there are no restoration costs. Right-of-way (usually by easement) is dedicated in the original plat.
C > Our electric monopoly, long-ago privatized, said in September and > repeated in January that it would cost ratepayers a million dollars a > mile to bury the lines. Overhead lines were said to be one tenth of > that.
That's a common rule-of-thumb for moving existing overhead to underground. But as Tony Toews noted:
Randall also wrote:
Or the wrath of local homeowners if it actually tried to do it?
Sure, if you're putting the cable in an open field. But try running your automatic trenching equipment down a backlot easement in an established residential neighborhood, working your way around tree roots, swing sets, fences, gardens, swimming pools, lawn-sprinkler pipes, dog houses....
Or try running it down a congested city street, working your way around sewer pipes, catch basins, water mains, gas mains, steam pipes, telco conduits, telco manholes, abandoned coal bins, abandoned streetcar rails, colonial-era cobblestones....
I agree that all conductors should be in conduit (although I must admit that I've been responsible for many miles of direct-bury CATV cable). Power companies routinely install transmission and cables in conduit, typically 4- or 6-inch Schedule 80 PVC, one conduit per conductor (and sometimes they provide extra conduits for telco, CATV, or whatever). Then they encase the entire bundle of conduits in concrete. The end result looks like a buried sidewalk three or four feet deep.
But doing all that requires a lot of hand work. Even if automatic trenching equipment is used to dig the trench, workers still have to place the conduits, build forms for the concrete, and guide the wet concrete into position. When the work is done, the trench must be backfilled, compacted, and the surface restored to as-was condition. Workers are also needed to pull the conductors through the conduits and terminate them.
Then there's the problem of finding space for transformers, splices, and switchgear. In suburban areas, you can put this stuff in big steel boxes above ground and hope that nobody complains. But in congested urban centers, there's no place for it above ground. So you either have to construct manholes or put it in the basement of a nearby building. You can imagine the difficulties these options would encounter.
You can put a lot of transformers and switchgear on poles, and most people don't even notice.
What's been your experience with NYSEG there in Trumansburg? Are they converting overhead to underground? If so, how are they placing the cables -- in conduits or direct burial? Where are they putting the transformers and switchgear? Who's paying for it? Are they burying telephone and CATV at the same?
For only ten times the cost of putting the stuff on poles....