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Utility poles

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Re: Utility poles

#91

Post by throwaway7645 »

ggm wrote: post #55
shirro wrote: post #29

Earlier quoted context omitted.

Except for South Australia. I don't know if it was due to termites, lack of hard woods, fireproofing or an excess of steel and concrete but we embed concrete between two steel beams to create the iconic stobie pole which has doomed countless motorists. https://en.wikipedia.org/wiki/Stobie_pole

Stobie poles are used a lot in Italy and southern Europe. They all seem to be from the 1920s and have really bad "concrete cancer" and the underlying steel is rusting out. Quite picturesque in a "oh crap, there is 220v on top of this rusting pile..." kind of way. "the prime of miss jean brodie" is set in pre-WWII scotland and an opening credit scene walks past two concrete lamp posts. My mother (who was an architectu…

220V isn't very high in the power world. The US has 765 KV. I'm not sure what the highest voltage cable in the world is, but now I'm curious.

Re: Utility poles

#92

Post by Scoundreller »

pan69 wrote: post #6

I have always wondered about utility poles, they always seem very fragile. Why not just stick everything in the ground?

Road salt and underground vaults isn't a great combo.

At the micro scale: Toronto Hydro had to start a campaign of replacing its handwells or spraying then with an insulating coating because children and pets were getting shocked.

https://www.torontohydro.com/sites/electricsystem/Documents/...

At the macro scale:

Mmoke from vault fire: Nearby building closed for 6 months for decontamination

http://www.cbc.ca/news/canada/toronto/rbc-hydro-vault-fire-t...

Re: Utility poles

#93

Post by caf »

Probably they computerized this back in the seventies, and the books are moldering in a closet somewhere.

Oh, sweet naive summer child.

Re: Utility poles

#94

Post by andmarios »

s_tec wrote: post #41

Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…

There aren't any mathematical tricks, rather how the real world (generator) translates to math.

The generator at the power company has 3 stators that are on equal distance between each other on a circle. As the rotor rotates, it induces AC voltage at each of them.

Because the rotor rotates at a stable speed, the AC voltage follows a sine function.

Because the stators are placed 2/3pi apart, their sine waves have a phase difference of 2/3pi.

Because 2/3pi+2/3pi+2/3pi=2pi, if you add them all together then you get 0 (sin[2pi]=0) and this is your neutral wire.

Quite honestly I learned that very late in the university which is a pity. Once you see how the real world translates to math, many things (like euler's formula which is of utmost importance for engineers) fall in place.

Re: Utility poles

#95

Post by Animats »

ThrustVectoring wrote: post #80
blattimwind wrote: post #67

Earlier quoted context omitted.

You can have a two phase power system[1], but two phase generators are less efficient and more expensive relative to three phase – for the exact same reason why power distribution is less efficient and more expensive relative to three phase. [1] two phases in quadrature, which is very different from split phase, which is not two phase at all.

IIRC these designs don't naturally have torque at zero speed like three-phase induction motors do.

Yes. One of Tesla's more useful inventions was figuring out an simple way to get a synchronous motor started. Pre-Tesla schemes involved auxiliary starting motors and clutches. Tesla figured out how to run a synchronous motor in induction motor mode during starting.

Re: Utility poles

#96

Post by femto »

A bit of information: Openstreetmap includes a field for the identification number on utility poles. A lot of people fill this field in when they do mapping (I do). Thus OSM is quite a good reference for these numbers, and the general topology of the electricity grid.

Re: Utility poles

#97

Post by losteverything »

The best example in my stats class on why sampling was used: working for the phone company he had to determine if poles were rotting. Practically speaking he could not use a random sample: he sent a pole climber to an area and while there, climb a few or several in the area. It would not be practical to climb one here, another 3 miles away, etc..

Re: Utility poles

#98

Post by thescriptkiddie »

ars wrote: post #68
s_tec wrote: post #41

Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…

> The electrical outlets in your home have two power-carrying prongs. Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. > and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volt No. The power prong (the smaller one) will switch from -170 to +170. The other one (the neutral) is always at zero (measured relative to yo…

Split-phase power is only common in the US and other countries with 120 volt (+/- 5%) mains. In the 230 volt (+/- 10%) world, it is typical to power single-phase loads either across two phases (delta) or between a phase and ground (wye).

Re: Utility poles

#99

Post by mirimir »

adonovan wrote: post #47

Those cans are filled with transformer oil, which until relatively recently consisted mostly of polychlorinated biphenyls or PCBs. Imagine how many of those cans exist across the United States and you get a sense of how big the PCB industry used to be, and why rivers such as the Hudson in New York [1] and the Housatonic in Massachusetts [2] are polluted with olympic swimming-pool sized quantities of the durable oily…

Yes, PCBs have high thermal conductivity and low electrical conductivity. Also better thermal stability than hydrocarbons. But unfortunately, quite toxic as well. And they tend to be contaminated with dioxins, which are far more toxic.

Seriously, PCB/dioxin contaminated oil sold for frying? That is insane. But then, people sometimes adulterate sugar with lead acetate :(

Re: Utility poles

#100

Post by phasetransition »

Dangeranger wrote: post #84
lovemenot wrote: post #53

Earlier quoted context omitted.

What's a typical range of amperage for a distribution line?

Most distribution transformers have a maximum rating of 200kVA. So depending on their voltage you can calculate the max amps by (200kVA / voltage). Minimum amps is a bit harder to calculate but I would make a best guess of 20% of the max 200kVA. You can read a bit more about the calculations here[0] [0] https://yorkcentraltechtalk.wordpress.com/2012/06/27/transfo... Edit: noted that 200kVA is the maximum rating, not…

Do the distribution transformers have "winter" ratings like the local center tapped step down transformers that feed houses? Around here it is pretty clear that Georgia Power doesn't pay much attention to the name plate ratings, winter or otherwise, when sizing and determining the number of homes per xformer.
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