Andrew_Culture
Internet Marketing bod
- Location
- The People's Republic Of Suffolk.
Does anyone know about suspension bridges???
- Thread starter Spinney
- Start date
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neil_merseyside
Guru
- Location
- Wirral
Aren't sink holes extaordinary with the implausibly steep sides.
Wobblers
Euthermic
- Location
- Minkowski Space
Swansonj will be able to give you more specific details, but those insulators are designed to withstand very high voltages (no surprises there, eh?!), of the order of 1000 kV (@swansonj, would I be right in thinking that this is a 400 kV line?). An insulator large enough for the job is an unwieldy beast, so it is composed of a number of insulating disks which are string together. Actually, the main problem is not breakdown of the insulator, or flashover through the air, but "creepage", where current will flow to earth along the surface of the insulator, particularly when it's wet, or conducting dirt coats the insulator surface such as might happen in industrial areas. To prevent this, multiple ribbed disks are used so as to increase the distance that the current has to travel along the surface of the insulator string.
Swansonj, if you don't mind yet more questions, what's the conductor cross section of those wires you're sitting on?
The other thing that occurs to me is you really need to have a good head for heights - respect!
I concur ....... Well , it seemed to work last time
swansonj
Guru
Yeah, pretty much like the man says.
That is indeed a 400 kV line which for reasons that will make sense to electrical engineers but would drive others to drink means the peak voltage is 326 (400 is rms of phase-phase innit) but we then have to insulate to withstand switching surges - so yes, best part of a thousand kV.
And yes, the whole thing is about designing those "sheds" (the individual disks) to shape them to minimise the chance of water forming a continuous leakage path along the surface. So they have a really complex shape with lots of re-entrant bits and sticky out bits on the bottom surface (which you can see bits of on the surface facing you in the picture). In really bad industrial areas we've sometimes washed them at intervals to prevent surface build up if pollution. Salt spray in coastal areas is a problem too.
Occasionally they shatter and an advantage of having lots of separate sheds is that you can replace just the broken one.
They're made of either glass or porceleine. We've been trying to develop composite insulators for ages and we've done a few pilots but when we deploy the new T-pylon that will have composite insulators (and phase-phase insulators too, another first).
The number of separate strings of insulators - 4 in that picture - is just a function of mechanical strength; we have designs with just two strings now for a tension set.
Those conductors are 27 mm diameter, McW. They were the workhorse conductor used almost universally throughout the fifties and sixties .... until we discovered, twenty years later, the corrosion problem between the steel core and the aluminium outer (oops). Now we use aluminium alloys that are strong enough to make the whole conductor aluminium without a separate steel core. Our largest is, from memory, 38 mm diameter (clearly we have a whole suite of conductors and we choose for each specific line depending on what rating we need, how strong the towers are, what ground clearance we have, etc etc). Not much point in going bigger than that as the skin depth problem starts kicking in (another one for us nerds, sorry, I mean electrical engineers). We also don't use bundles of four conductors ("quad" in our jargon) anymore - they turned out to be prone to a completely different aerodynamic problem under ice build up called galloping, more akin to what happened to Tacoma Narrows. It's all twin or triple now (you can't use single conductors above 132 kV because they are too noisy).
For the avoidance of doubt, I should say that I was never a linesman. I just needed to do some measurements on overhead lines so went through enough of the linesman training school to be certified for the basic access and egress. But I then had some extremely enjoyable and satisfying days up pylons ranging from urban Birmingham to rural Yorkshire.
Globalti
Legendary Member
Harmonic vibration is a problem on road vehicles with complex transmissions - my brother was a chassis and powertrain Engineer at Land Rover and explained that the big lumps of iron sometimes found bolted to Land Rover transmissions are put there as a post-production solution to unforseen harmonic vibration.
Motorbikes sometimes have bar end weights to prevent steering wobble:
Motorbikes sometimes have bar end weights to prevent steering wobble:
GrumpyGregry
Here for rides.
Fascinating. I never realised the core is carrying less of the AC than the "skin depth". Ain't science wonderful?
Wobblers
Euthermic
- Location
- Minkowski Space
Yeah, pretty much like the man says.
That is indeed a 400 kV line which for reasons that will make sense to electrical engineers but would drive others to drink means the peak voltage is 326 (400 is rms of phase-phase innit) but we then have to insulate to withstand switching surges - so yes, best part of a thousand kV.
And yes, the whole thing is about designing those "sheds" (the individual disks) to shape them to minimise the chance of water forming a continuous leakage path along the surface. So they have a really complex shape with lots of re-entrant bits and sticky out bits on the bottom surface (which you can see bits of on the surface facing you in the picture). In really bad industrial areas we've sometimes washed them at intervals to prevent surface build up if pollution. Salt spray in coastal areas is a problem too.
Occasionally they shatter and an advantage of having lots of separate sheds is that you can replace just the broken one.
They're made of either glass or porceleine. We've been trying to develop composite insulators for ages and we've done a few pilots but when we deploy the new T-pylon that will have composite insulators (and phase-phase insulators too, another first).
The number of separate strings of insulators - 4 in that picture - is just a function of mechanical strength; we have designs with just two strings now for a tension set.
Those conductors are 27 mm diameter, McW. They were the workhorse conductor used almost universally throughout the fifties and sixties .... until we discovered, twenty years later, the corrosion problem between the steel core and the aluminium outer (oops). Now we use aluminium alloys that are strong enough to make the whole conductor aluminium without a separate steel core. Our largest is, from memory, 38 mm diameter (clearly we have a whole suite of conductors and we choose for each specific line depending on what rating we need, how strong the towers are, what ground clearance we have, etc etc). Not much point in going bigger than that as the skin depth problem starts kicking in (another one for us nerds, sorry, I mean electrical engineers). We also don't use bundles of four conductors ("quad" in our jargon) anymore - they turned out to be prone to a completely different aerodynamic problem under ice build up called galloping, more akin to what happened to Tacoma Narrows. It's all twin or triple now (you can't use single conductors above 132 kV because they are too noisy).
For the avoidance of doubt, I should say that I was never a linesman. I just needed to do some measurements on overhead lines so went through enough of the linesman training school to be certified for the basic access and egress. But I then had some extremely enjoyable and satisfying days up pylons ranging from urban Birmingham to rural Yorkshire.
Thanks swansonj, I've learned something today.
mybike
Grumblin at Garmin on the Granny Gear
- Location
- Not 'emel 'empstead
I hadn't realised the effect went down so low in frequency, but then you are talking about high current/high voltage.
swansonj
Guru
Well, most of the time at 50 Hz you can indeed ignore it, it's only when your conductor gets really fat it's a problem. It's more of a problem with underground cables, (a) because they're fatter and (b) they're copper, which has a higher conductivity and hence lower skin depth than aluminium. So underground cables have quite complex multi-helix patterns of the individual strands so that each strand takes its share of being at the centre. I just happened to be looking at the spec sheet of a cable they're installing up north somewhere yesterday (how's that for a coincidence) and I happened to notice the skin depth factor in the rating schedule was of the order 1%.
vernon
Harder than Ronnie Pickering
- Location
- Meanwood, Leeds
Motorbikes sometimes have bar end weights to prevent steering wobble:
No they don't. They fit steering dampers to prevent steering wobble not that it's a problem for most bikes under ordinary riding conditions. Bar end weights are fitted to reduced the resonance of some bars which can make the hands go numb and.or blur the image in the mirrors. Most weights are bling as they are not needed in most cases.
An easy way to stop mirrors resonating is to stick a blob of Blutac to the mirror glass. Not very aesthetic but very effective.
swansonj
Guru
My daughter's trombone teacher has attached a piece of gaffer tape barely one inch long to her trombone and swears it improves the tone.
subaqua
What’s the point
- Location
- Leytonstone
Yup, even your bootlace 1.5 4 core SWA ( about the smallest TPN cable) is constructed with a twist. One of the main failures of cable approval is the twist is incorrect . It's good being a Nerd , sorry , electrical engineer.
Furthest up a pole I got was 11kV install to pole Tx and jointing and hated it in the winter.
mybike
Grumblin at Garmin on the Granny Gear
- Location
- Not 'emel 'empstead
I was always amazed at how cold your feet got in winter, mind you, that was as an apprentice & just watching.
GrumpyGregry
Here for rides.
I have a brass doodad, I call it doodad becuase the name escapes me. It clamps to the headstock of an electric bass. It certainly changes the sustain and the sound of the instrument. Even had it rigged up to an oscilloscope by a real live rocket-science.
Now is the extra sustain and changed tone an improvement...? That would be pretty subjective.
