There are two other benefits to bundling:
- it significantly reduces the inductance (and hence the voltage drop),
- it improves cooling of the conductors. At full winter load those 400 kV lines are carrying about 3,000 amps per bundle, so they do tend to get a bit warm.
care to elaborate ?
you arent talking about their use of torture at Abu Ghraib and Guantanamo are you ?
Judging by the local lines, both voltages can be either. The recently refurbished line was reduced from four to two, but with a wider slightly cranked spacer. Parts of the old line, mainly over roads had the bundle of 4 spacing increased by about 50% apart from at the pylons.
An older line had the middle conductor on one side (2 wire) tilted at 45 degrees, by being the opposite conductors of the usual square. I can only think that this was for identification. Is there any other reason?
Don't see the connection to domestic electrics... hardly rocket science is it? ;-)
Even monkeys fall out of trees...
Hard to choose one really... we had a long thread on this a while back.
In general they seem to have a lower level of "respect" for the electrical systems in houses - possibly due to lower perceived risk from the 110V supply they mostly use. However the lower supply voltage (hence higher current and heating effect) combined with the permitted use of poor wire jointing technique (twist on "wire nuts") and extensive use of aliminuim cable seems to result in far more electrical fire risks.
AAUI the quality of their switch gear and accessories is lower (paper used as insulators etc). They often don't have RCDs. Their circuit breakers often lack the "magnetic" response facility that is standard on ours, and ensure that high overcurrents are cleared very quickly.
They are also pretty poor on earthing systems (like not even having one on some socket circuits!), and equipotential bonding. The lower voltage and poorer MCBs makes earth fault loop impedances far more critical, and it can be very difficult or impossible to achieve rapid disconnect times.
Try this thread for more:
Not exclusively. 2 conductor per phase 400kV started being used in the UK in the mid 90's and is now being used for a lot of restringing and for all new routes.
Twisted joints, held together by some sort of ceramic or plastic thimble.
I think I am. How is the field strength diminished by having multiple conductors in close proximity ? (My AC knowledge is very sketchy.) It's voltage-determined, is it not ? I'd assumed multiple conductors were used simply as a compromise between current, heat generated, weight, and ease of construction.
It isn't long since this topic became a long running argument in the newsgroup. Lets not go down that road AGAIN.
On Thu, 6 Oct 2005 12:42:08 +0100,it is alleged that The Wanderer spake thusly in uk.d-i-y:
Sprung steel coil actually, and they burn up significantly less often than strip connector.
I've also seen plain ceramic thimbles with nothing else in them....Scruits they used to be called.
On 6 Oct 2005 18:27:19 GMT,it is alleged that "Bob Eager" spake thusly in uk.d-i-y:
Yes, nasty things they were too. US Lighting manufacturers still produce a plastic equivalent that isn't UL Listed for anything at all (not that the dang things actually fit the wires either).
Admittedly the old versions without the steel spring were a little 'pointless'. The modern ones are the result of years of development, and counterintuitively provide a very good joint with copper-copper.
With alumin(i)um wiring, all bets are off, most US electricians suck air in through their teeth and start mentally making out a replacement bill when they find it.
It's actually 100 times a second. The 50 Hz refers to a full cycle - from zero to + then zero to - and back to zero. Relative to *both* conductors.
What causes harm is potential difference. You could have a million volt supply, and if one side is earthed you should be able to touch that conductor safely. But not the other one...;-)
In an ideal world both neutral and earth are at the same potential.
This is basic electrostatics and is the same at DC. Field strength is potential gradient. The field close to the surface of a round wire carrying a given charge per unit length is inversely proportional to the radius of the wire. Thus field concentration and the risk of breakdown always occurs near sharp edges or points. A rough engineering approximation for more complicated structures is to think of the field as proportional to one over the radius of curvature of a structure component. That's why much of the metalwork of high voltage equipment has smooth rounded edges.
You can visualise it in terms of field lines (lines of flux) being more crowded together near a feature of small radius. High electric flux density implies high field strength since the two are proportional to each other, the constant of proportionality being called permittivity.
Its years since I studied this aspect but from memory the bundle of conductors "looks like" a single larger conductor with an effectively larger diameter and thus a reduction in stress/corona is achieved. Someone else might be able to recall better from less aged studies? The 4 conductor bundles associated with 400kV are relatively easy to visualise this but 275 kX with 2 conductors must "look like" an oval I suppose. As a matter of interest I had a tour round Drax power station about thirty years ago and the primary connections between the station and the grid switching breaker farm were run in single heavy bars for a short distance. The noise of frying air molecules was astounding.
Thanks John. Your explanation was better in helping me understand why separating the conductors would have an effect.
I had a staff tour around Fawley many years ago. We didn't go out to the transformer room as the guide said he didn't like being out there ! We did get to open up one of the furnace inspection windows to feel the heat coming off it (did you know furnaces are hung from the roof to allow expansion downwards and outwards?). I've also worked for a few days in a coal station in Notts. The noise around the ball mills can only be described as mind-numbing.
Quite possibly relatively thin-wall hollow bus-bar sections.
Nobody has yet mentioned skin effect (until now).....
They are solid copper running at around 22kV from the generator to the generator transformer but these are totally out of sight in normal operation. On the HV substation itself they use hollow copper or more usually nowadays aluminium - but I'm not sure if you can really call
100mm diameter and 20mm wall thickness tubing "thin wall"Occasionally on 132kV sites overhead line cable was also used as a flexible busbar. Most new switchgear (and busbar) installations are metalclad using sulphur hexafluoride gas as insulation. They occupy a fraction of the land area of an air insulated site.
Ah! I guessed someone would be along to air their knowledge!
Hmm, let's see, fault levels should be worth a bit of discussion....
:-)
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