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 poison.
PCBs were used because they are really good thermal conductors, which is the same property desired of cooking oil for frying. In recent years, thieves in Kenya (which has yet to replace PCBs with something less toxic) have been vandalizing [3] transformers and selling the oil to street vendors, which has the twin effects of destroying the fragile electrical infrastructure and poisoning the neighborhood.
There's a nice recreational lake here in Raleigh, NC. People run on paths by it, sail on it, and used to fish out of it. Sadly, it’s also an EPA Superfund site because a company long since out of business, Ward Transformers, saw fit to dispose of PCB-laden transformer oil right into a ditch behind the plant. The PCBs ran off into the lake and streams for miles. All the nearby waterways warn not to eat the fish caught therein.
This company wasn’t just irresponsible, it was malicious. At one point, a contractor it hired to dispose of the oil was caught spraying it along rural roadsides.
Dirt and gravel roads were commonly oiled to keep down dust, and eventually create something like macadam. But they tended to use the least expensive oil available. Such as used motor oil. Which, back in the days of leaded gasoline, contained considerable lead.
The story about Kenyans selling PCB oil is truly sad. I cannot imagine the damage that is doing to children and families in that country.
It reminds me of the Vice News story about the illegal oil refineries which are present in the Niger River delta and the environmental and humanitarian destruction they are causing.
Additionally when authorities find illegally refined oil they simply dump it on site, contaminating the villages and markets where it is stored.
I used to know a fellow who spent some years working for "the oil industry" in the far east. That would be a couple of decades ago.
He really enjoyed the street food. But, as he told me, you had to be careful. How did a vendor have fresh fare without power nor evident means of fresh supply and cooling?
Well, per him, some vendors kept supplies submerged in formaldehyde.
I've never looked up independent confirmation of this, and I haven't been there and so had to worry about it. But he was, in my experience, a straight shooter and not one inclined towards tall tales.
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 :(
It's kind of astonishing how far people will go in the absence of a punitive regulatory environment. One of my favorite books in Project Gutenberg is this 1820 treatise on the adulteration of foods: http://www.gutenberg.org/ebooks/19031
Everything from copper to make pickles green, to molten lead to clarify wine.
And if they aren't adding poison, the wikipedia article links to a prior incident where 12 babies died from malnutrition, due to watered-down baby formula.
Such callous disregard for life (human and animal) is beyond comprehension.
And melamine. It wasn't added as a sweetener. It was added to boost apparent protein content, because it was less expensive than actual protein. As I understand it, the simple test for food protein content reported melamine as protein.
I get the sarcasm :) But in fact, markets are great for many things. However, they're clearly vulnerable to information asymmetry and outright dishonesty, at least in the short term.
I mean, demand for PCB-tainted oil for dust suppression did decrease dramatically after PCB content and toxicity were widely known. And demand for melamine-supplemented baby food also decreased dramatically after people discovered the issue.
The problem was that more-or-less irreversible damage had already been done. Damages could be recovered through litigation, perhaps. But that doesn't fix poisoned ecosystems and children.
So we need regulation to punish market manipulation through dishonesty.
> So we need regulation to punish market manipulation through dishonesty.
That's not the only source of problem. Another is managing the game theory of externalities. For example, if every transformer manufacturer is dumping its PCBs into rivers, no one manufacturer can afford to make "clean" transformers that dispose of PCB byproducts in a more ecological way as transformer buyers will presumably buy the cheapest one that meets the necessary performance characteristics. Regulation can add management of the ecological externality as a mandatory performance characteristic, disadvantaging no manufacturer relative to all others.
> In recent years, thieves in Kenya (which has yet to replace PCBs with something less toxic) have been vandalizing [3] transformers and selling the oil to street vendors
I see no confirmation on this. Sounds like an urban legend. All reports come from the one source which also talks about the legitimate reason of scrap stealing.
The doctors quote should be the biggest tip off.
If it makes people sick(Off what seems like a once off) why would street vendors use it? This is just nonsense.
Why do we demonize people from the underdeveloped world. Whats the point of cheap oil if your customers never come back. It lacks basic commercial sense. How can this become widespread.
Nonsensical urban legends on the other hand I'd guess they catch like us.
Another Urban Legend - transformers contain P2P, which tweakers drain them for. It's interesting lore at least, they are a big part of the community.
After further digging I think you're probably right. Variants of this story seem to have been reported in many countries over many years but none cites an actual authority such as government report or scientific paper. Copper theft does seem more likely.
I absolutely love reading about a topic from a super enthusiastic non-expert. I want to subscribe to a weekly series called "Reasonably Intelligent Person Obsesses Over Something"
Thanks! Can I suggest that you might enjoy following my blog regularly? In addition to utility poles, I have also discussed this year: Samuel Johnson's feud with James Macpherson, a fraudulent poet; the panicked history of England in 1533 after Henry VIII's mistress got pregnant; the Slaughter electric needle injector; how plutonium is used to power medical devices; equivalents of "Joe Blow" in Turkish and Hebrew. Also a lot of other stuff more or less random.
Why do you denigrate your own work so often, though? Most of the time, when someone posts your articles, you reply "does this guy ever shut up" or "this post sucks".
In Firefox, you can just visit https://blog.plover.com/index.atom or https://blog.plover.com/index.rss and the browser will present you with a button that says “subscribe to this feed using live bookmarks” which will add it to your Firefox bookmarks, and it will look just like any other bookmark folder, except that it will always contain the dozen or so most recent posts.
Probably other browsers have something similar, either built-in or supplied as a plugin.
Something that completely fascinates me are cell towers/equipment. They are everywhere, yet I know almost nothing about them and rarely get to see them up close. Even less often (pretty much never) meet anyone who work on the equipment. I imagine each base station is basically a mini datacenter. I was at Mammoth Mountain recently for the first time and got to see the cell towers at the top of one of the lifts up close and got some good pictures.
The one thing I miss about working for a major national telco was access to the internal newsgroups where you'd get deep discussions triggered by someone's random question on things.
I would absolutely love a big writeup on how they're set up and what the components are, as well as all the real-estate stuff that certainly surrounds them. I'm also noticing a lot of new towers that look like big cylinders on a pole, sort of like a TACAN so I often wonder what's up with that.
I do know that the traditional ones are triangle shaped such that they each form the intersection of a hexagon tessellation (hence the cell in cellphone) such that you have three towers pointed into every hexagonal cell.
Microcells are good for carrying lots of traffic from lots of mobile stations. In rural areas, coverage at the lowest cost per square mile is more important. Also, farmers aren't always near the highway, so microcells on the highway would not work well for them.
I don't know, maybe this sort of thing was better before Wikipedia? Now an hour or two of reading can answer pretty much all of this person's questions.
Back around 2010 I worked for a company which built software to catalog residential distribution utility poles and the lines emanating from the poles to the houses.
To elaborate on a few of the statements from the post
Poles in my neighborhood tend to have consecutive numbers. I don't think this was carefully planned.
The sequential ordering of pole numbers is definitely planned, and fits in with a scheme developed back in the 60s-70s which made documenting the poles lifecycle in paper records much easier. The poles are numbered sequentially with prefix numbers generally indicating which substation district the pole belongs within. Distribution utilities think about their infrastructure as a network of substation circuits. You should be able to tell which circuit you are on based on the numbering on the pole.
There are three because that is one way to change the three-phase power to single-phase, something I wish I understood better. Truly, we live in an age of marvels.
Not all distribution systems use three phases, some use two, some use single. It all depends on where you are in the system and the general layout of the circuits within the distribution network. Also not all distribution is 7kV, some are 12kV, and some are 25kV. Again this all changes based on the properties of the system, and the qualities that are being optimized for by the power engineers.
I have tried to imagine what the number-burning device looks like, but I'm not at all sure. Is it like a heated printing press, or perhaps a sort of configurable branding iron?
This can be done a number of different ways, but one of the common ways is with a laser engraver. This is a fairly recent practice, so I am not as versed in the operational details as with traditional tagging. Another means of tagging which is not covered in the article is carving the numbers into the pole with a physical etcher, similar to a wood router.
Without the Internet I would just have to wonder what these were and what OSMOSE meant.
OSMOSE was at the time of my work in this field, the largest such company that dealt in the support and maintenance of residential utility poles. They have some very interesting proprietary mechanisms for managing inventories, and are generally a very smart group of people. My guess is that they collect all the inventory and survey maintenance of poles using mobile LiDAR and machine vision now, as that was what we were speaking to them about at the time.
The pole numbering also helps in things like the work PG&E has to do checking for trees and other obstacles posing a risk to transmission lines. The report indicating where the work needs to be done (for instance to cut down a tree) uses the pole number as a point of reference.
Not just utility related reporting uses the pole numbers.
My father was the volunteer emergency service coordinator (and power station operator) in the tiny town where we grew up. his use of road names + power poles ids + direction & distance was frequently complimented by the accident investigators when they came to look at shit (and later the court cases for some)
Remote areas with 10s of KMs of power line and 0 other features :|
Yes, I am intimately familiar with this as this was also part of the services that I was involved in delivering. One of the deliverables for utility clients we provided was every "fall in" or "drop in" line violation for high power transmission lines, including their "between" location in relation to adjacent poles on the corridor.
I could talk about this subject for hours so let me know if you have any other questions.
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]
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.
Distribution transformers are not usually thought of as having a winter rating. On the other hand, distributions lines definitely do. Sometimes work on lines can only be done during the winter, because the load has to be shifted to lines that can only handle the increased temporary load during the winter.
There is a science and an art to sizing residential xfmrs. Generally is depends on the square footage, number of bedrooms and type of fuel used to condition the house.
Probably where GP is running into problem(like most electrical utilities) is that the use of electricity per square foot keeps going up.(caused by the increase of electrical devices in the home) So while the xfmr might have been sized correctly when installed 20-40 years ago, it is no longer sufficient. This causes problems.
Source: I was a distribution engineer for 7 years.
Thanks for the info. Day job has me using the NEC frequently, and occasionally the NESC.
But I never thought about pole xformer sizing until this house. Our 35kVA (summer) faceplate xformer services nine homes. Even though it browns, it keeps on working. They've got a lot of margin, it seems
My country is divided into a very very fine cartesian grid, and each pole is referred to by the grid number, which is also its database reference id for transformers and other hardware... a homegrown GIS. A consistent grid also makes it easy for linemen to find them!
Fascinating, this seems like a nice solution for "Where is this pole?" sort of questions from the back office. I wonder if they combine that numbering system with other IDs such as "Which circuit is this pole on?" tagging.
Two phase power is very, very rare. You are probably thinking of split phase power which is a form of single phase power. It is ubiquitous in American residential power. It takes the form of two hots at 240VAC with a neutral between them, allowing you to get 120VAC from the neutral and either hot.
> There are three because that is one way to change the three-phase power to single-phase, something I wish I understood better.
No, that's not correct.
Three transformers is for changing 3 phase medium power, to 3 phase regular voltage (for commercial customers).
For single phase home customers, you run a single one of those phases along a street and attach center tapped transformers to it.
The center tap means from the top to the center is 120v, and from the center to the bottom is another 120v. This gives something called "split phase", and is how homes in the US are wired.
This allows you to get 240v in the house if you need it by attaching to the top and bottom of the transformer.
The center tap of the transformer is also attached to the ground, and to the neutral power line (back to the generator). This gives what is called "zero voltage" (voltage is always relative, there is no such thing as absolute zero voltage - so you just have to pick something, and call it zero).
FYI, this is the correct description of the vast domestic power in the US, which is a single phase of distribution on the primary side to a center tapped secondary transformer.
"For single phase home customers, you run a single one of those phases along a street and attach center tapped transformers to it."
True but there are a few variations. And you also have to remember that each of those single-phase lines runs back (at some point to a three phase transformer. One very important facet of creating the single-phase spurs is to make sure the load is reasonably balanced.
Three phase 240 VAC is also cheaply converted to 120 VAC single phase in the same transformer by putting a center-tap into one side of the transformer's delta-connected coils. You will get 120 VAC from that center tap to either of the adjacent hot connections but you'd better not connect anything between the center-tap and the opposite hot connection!
Going to be a bit pedantic here but you absolutely can have 0 Voltage. Voltage is the potential energy created by a difference in charge between 2 points. If you have a mass with sufficient free mobile charge, when you inject additional charge into it, it will rearrange the charge within itself to cancel out in injected charge resulting in 0 Volts of potential. This is the principal that a ground connection works on and why you don't have voltage inside of metal conductors, just on the surface.
If you have any conductive bar or wire of sufficient size you can safely touch both ends (and measure zero volts across them. If you stretch those conductors over miles and miles of distance, it gets harder to reference the end to both grounds at the same time. And getting a good ground can be hard. There are numerous stories of "stray voltage" making cattle jumpy, etc.
Of course if you coil up that conductor and pass a magnet by it you're going to get shocked ;)
My dad was an electrician for about 40 years - one story he told me when he was training apprentices years ago was teaching them how to climb telephone polls. You wore boots that had spikes in the side of them, but when climbing, you had to keep your knees away from the poll so the spikes would dig in properly. Unfortunately, when you get to the top of the pole and look down, some people panic due to the height. And when they panic, they tend to "hug" the poll, which causes the spikes to pull out, which causes the person to slide down the poll which is pretty much a collection of splinters in poll form. They called it "burning the poll".
I did some work for an electricity utility and they wanted to get the pole IDs described in the article into our database, alongside the GIS data. The client explained that getting the IDs was kinda difficult and there were several different data sources for the various regions they provided service to. By and by we found a guy there who knew how everything worked and promised he'd get us the data that we needed - which he did.
But he told me an interesting story - the utility had about 50,000 power poles in their network. But due to various historical reasons and how their assets were digitized over the years he reckoned there were probably about 1000 of them that were on their maps, but that didn't actually exist anymore. And interestingly, he thought the inverse was also true; that there were perhaps 1000 poles out there that weren't on any of their maps. Big ten meter tall poles, some probably carrying live cables - didn't know they were there.
> that there were perhaps 1000 poles out there that weren't on any of there maps
I can totally see how this would happen. When I bought my house, the power/utility lines were hanging about four feet off the ground in my backyard. Apparently the previous owner didn't care.
I called the utility company to complain, and they sent someone out with a new full size pole, who basically just shoved it in the ground in the corner of my property to prop up the lines.
As far as I can tell, there are no identifying marks anywhere on the pole. No label, no inspection, no nothing. Except a sign that says "Danger, do not put ladder on this cable", which is on the fiber optic cable that runs along the pole.
This is common at every utility. Part of the issue is based on the fact that the GIS systems do not align with the paper systems 100% and the paper systems are typically regarded as the standard.
Another problem that must be considered is that utility workers, while highly competent at their profession, are not always great with working on computers. They generally write everything down on paper and then have one of the younger linemen input the changes into the electronic records system.
Also utilities often have several record systems in place, some being GIS based, and some being mobile computer based with check in with a central database. These systems are almost never developed and worked on by the same people, so inconsistencies abound. It's normal for the inventories to diverge, and for updates to take weeks to propagate from one system to another.
> "Another problem that must be considered is that utility workers, while highly competent at their profession, are not always great with working on computers."
You're absolutely correct on this point. When I was working as a transmission system operator the older guys (all in the 50s and 60s) would complain all day and night about the new "computer apps" that were introduced in our day to day workflow. They all preferred the old "pen and paper" way of doing things...Like you said, I'd be the who would end up putting the written switching procedures into the application we used since the older guys basically refused to learn it...
This is still a major problem in distribution. Some of the best workers are in their late 50s and they are familiar with older equipment in the field that the younger guys may have never seen.
They would much rather use pen and paper to report what they did or didn’t do, with little appreciation for the reporting that could be done with a bit of input on the computer.
Do your system operators us GIS to sectionalize lines and troubleshoot transmission/distribution issues, or are you talking about the engineers/planners?
Both sides use GIS to do their jobs. The scada part is a little different since one-line diagrams are all that is needed for that. But the dispatching is all GIS based.
We make significant revenue based on accurate maps and good data as well. Just fixing our attachment rental inventory and keeping it accurate pays for all of the GIS system and upkeep with money to spare.
I'm familiar with the SCADA part (I work as an EMS/SCADA devloper), but before my current role I was actually an operator and we used "red-line" drawings in conjunction with the SCADA system to troubleshoot down lines/relays/lockouts/etc. They were all digital for ease of use. On the transmission side of the house we didn't use GIS all that much, but the DOC folks used it as their primary source.
Pole replacement is interesting and full of bureaucracy. At least here in Seattle, the power company doesn't have authority to move communications wires and equipment attached to poles that are being replaced. So often times they'll cut the bottom off the old pole, move it to the side, install a new pole, and then use seemingly whatever they've got lying around to lash the two of them together. Owners of the other equipment eventually get around to moving their stuff (sometimes years later), and the last one removes the pole.
Old utility poles can be reused in many ways too, but they must be outdoors, and not where it can have direct contact with people. Back in 2003 I called a local electric company if they could donate a few used poles to be used as beams for a bridge I was constructing for a local park. They we're happy to oblige. You can sometimes see these poles used in retaining walls and buried alongside hiking trails, used as water bars. I keep an eye out whenever I'm on a trail and am sometimes surprised to see an electric pole miles from a trailhead.
> and not where it can have direct contact with people.
Could you expand on that? My elementary school had a playground structure made of old utility poles. Other than getting pitch on our clothes, they didn't seem particularly hazardous.
They're treated with lots of preservatives. They're probably not all that dangerous in the short term (unless you eat some of the pitch), but it's annoying to deal with the potential long term safety. My scoutmaster worked for the power company, and I was going to ask him if we could have a couple of poles for my Eagle project, but after looking at what you had to do to reuse them I decided it was simply too much of a hassle.
Like pressure treated lumber, the chemicals used to make the poles less susceptible to bugs/rot/etc can be hazardous to people. Until a few years ago, arsenic was one of the components used -- in commercially available pressure treated lumber. I suspect the same chemical cocktail has been used in poles.
(edit -- add commercially available lumber clarification)
I'm not an expert, but I can guess it depends on the pole and how it's been treated. The company I called gave me a list of disclosures and guidelines for re-use. Maybe the poles you see haven't been treated with such-and-such chemicals.
Haha, I was joking but the substance is tar-like and won't come out easily (sat on a creosote bridge once). We have some plants in my area that make it as well...I'm kinda scared what the long term impacts will be healthwise as you can sure smell that chemical-tar-oil compound.
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 constantly switching directions. At one moment, the left wire will be +170 volts relative to the right wire, and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volts. They continue trading places, completing a cycle every 1/60 of a second.
At some point in this cycle, the voltage difference between the two wires will be zero, which means that no power will be flowing at that moment (power = voltage * current). On the average, the wires will deliver the same amount of power as-if they had a constant 120 volts between them, which is why people say that electricity in the USA runs at 120VAC. The peak-to-peak voltage is 170V, but the "RMS" average voltage is 1/√2 of that, or 120V.
Anyhow, those brief moments of time where no power is flowing are a problem for a power company, who would like to deliver energy in a continuous stream. So, they build their power system with three wires. Each wire reaches its maximum voltage 1/180 of a second after the previous wire. Since the voltages on each wire are sine waves, when one wire is at 0, the other wires are at +√3/2 and -√3/2 of their maximum voltages. Therefore, there is no point where the power stops. In fact, due to a mathematical quirk, the power delivery is actually constant, even though the voltages on the three wires are constantly changing.
Turing three-phase voltage into two phase voltage is pretty easy. Just pick any two of the three wires and hook them into the home. The difference of any two sine waves is just another sine wave at the same frequency, so you automatically have single-phase power. In practice, the power company will try to balance the load between the three pairs of wires by sending different pairs into different houses or even neighborhoods.
Edit: As several people have pointed out, this isn't quite how it works in real life. See the comments below for details about the hot vs. neutral wire and how both 240V and 120V are available in the home at the same time.
> 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 you).
> Turing three-phase voltage into two phase voltage is pretty easy. Just pick any two of the three wires and hook them into the home.
This is not what they do. If they did they would not be able to have a neutral, and you would also not have an option of 240v. Homes don't have two phases, they have split phase.
> Just pick any two of the three wires and hook them into the home.
In actuality the phases have 240 volts between them, not 120. And from any phase to neutral is 208 volts (which some devices make use of). (Those are voltages to customers. Internally they use other voltages - in particular when they use a single phase, power a street with it - they care about the voltage to neutral, not the voltage relative to another phase.)
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).
>> 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.
Voltages are about potential differentials, so "zero volts" is relatively meaningless without context.
The neutral line is required by the electric code to be connected to earth at the electric panel, but even if it were not, any ungrounded appliances would work correctly.
Both prongs absolutely carry power. Slap an ammeter on the neutral line; it should be identical to that on the hot line. Don't actually do this, but if you were to cut the neutral line with a live circuit, you would see sparks. This is particularly important when working on circuits with a shared neutral (two hot lines on alternate halves of the split phase with a single neutral line); despite the breaker being off for your hot line, you can get shocked when working on junction boxes for the neutral line. Yes this is up-to-code in all states (though a few places either recommend or require ganging the circuit breaker when doing so).
>> 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 you).
Here you use voltages as a relative measure, which is correct. As a nitpick you do assume that the person is grounded. Walking on carpet in the winter, I can be at a potential of thousands of volts away from that though.
[everything from here after in ars's comment is correct and I have no more nitpicks]
If you are going to take the view that the neutral does not carry power, then the phase wire does not either. Ignoring volt drop, both wires have a 0V difference between each end and so no power is dissipated in them. Power is only dissipated in the appliance (except in reality, where volt drop is responsible for significant losses between generator and consumer)
>Both carry current. But not power. Power is volts * amps, and the neutral is defined as zero volts (if you ignore the voltage drop).
What he has already pointed out is that voltage is a relative unit. Zero volts by itself is meaningless. It would be just as correct to say that the hot wire is at zero volts and the neutral wire and the rest of the planet are at 120VAC. Also earlier you mentioned that from phase to phase inside a house was 240v but phase to ground was 208v. This isn't correct and it's simple trigonometry to prove why. You can visualize voltage potential in any polyphase AC system as the distance between points on a circle. Ground is the center of the circle and the individual phase is a point on the circle offset by the phase angle. For a split phase system there is 180 degrees between the two phases and cos(0) - cos(180) gives you the fairly obvious distance of 2x the radius. This means for 120v from phase to ground you get 240v phase to phase. In a three phase system there's 120 degrees between phases so if you have 120v from phase to ground you have (cos(0)-cos(120))*120v=208v. For what you're saying to be possible you would need 98.85 degrees between phases which is obviously not a nice integer division of 360 degrees.
High voltage transmission lines can carry power without a neutral wire because they use the earth as a neutral, but in your house you can be damn sure the neutral is carrying power. Cut off the neutral blade on your appliance if you want to check it out.
"Electric power in watts produced by an electric current I consisting of a charge of Q coulombs every t seconds passing through an electric potential (voltage) difference of V is
P = work done per unit time = VQ/t = VI
Note that V is the "electric potential difference" and it take two conductors to supply power.
I think it's incorrect to say that a single wire "transmits" power. Both a current and a voltage difference need to be transmitted to transmit power. So it's really the distribution system as a whole (in this case, neutral and hot together) which transmit power.
> Don't actually do this, but if you were to cut the neutral line with a live circuit, you would see sparks
Only if something were actually drawing moderate current to cause the arc. But yes, one side of that cut is likely to end up "hot" and could give you a decent shock.
> the voltage in those two power-carrying wires is constantly switching directions
I'm not buying this (in the USA). I've been in my breaker box. For a typical 110 volt outlet, the black (hot) wire is connected to the breaker, which is connected to one of the wires coming into the house from the street. The white (neutral) wire is connected to the same ground bracket that the bare (ground) wire is connected to.
240 volt connections (like my dryer and range) are taking a hot line from one of the lines coming into the house and another hot line from the other line coming into the house. You can see it on the bus bars in the breaker box. That's why dual breakers are used. Adjacent breakers pull for different bus bars.
Right, that is correct. To understand how that works, you have to realize that there is no such thing as an "absolute voltage", only the voltage difference between two wires.
In a breaker box, one wire (white) gets tied to ground, and the other wire (black or red) goes between +170 (relative to ground) and -170 (relative to ground). The black and red wires are 180 degrees out of phase, so when the black wire is at +170, the red wire is at -170. This gives a 340V peak difference between the black and red wires, which averages to 240V. You get your normal 120V outlet power between the hot legs and ground/neutral, and you get your 240V dryer & water heater power between the two hot legs themselves.
So, in a normal outlet, we can safely say that one wire is "more positive" than another, and that this flip-flops through time. When we look at voltages relative to ground, though, one wire stays put at 0V while the other goes between +170 and -170. It's just a question of where you put your reference frame.
There are two phase wires and one neutral. Diff between phases is 240V, the diff between any phase and neutral is 120V.
In Europe, you have three phases (R,S,T) and neutral. Here the diff between any phase and neutral is 250V, and the diff between any two phases is 380V.
In Europe, you have three phases (R,S,T) and neutral.
Is that everywhere, to every building?
In the USA, of necessity, power generation is three phase, large scale power distribution is three phase. What's confusing is that the previous discussion didn't differentiate between residential and commercial.
In USA residential areas nobody gets all three phases to their house or apartment. As discussed in previous comments, a house gets two hot wires and a neutral. In fact, to save money, sometimes entire neighborhoods only get one or two phases[1]: "spur lines" branching off the main line to provide power to side streets often carry only one or two phase wires, plus the neutral
In commercial and industrial settings it's common and necessary to deliver all three phases to the building. E.g. large electric motors require all three phases.
The explanation in that paragraph is not necessarily incorrect, just confusing because it talks about voltage "in" wires and isn't clear about what two terminals are being referenced.
It is true that the voltage between live and neutral changes sign, so neutral is sometimes 170V above live. But neutral is almost always at ground, and live goes to -170V relative to ground.
That last paragraph though seems wrong, so OP may have been confused himself when writing.
This isn't true in your home. The neutral is bonded to ground at a single point, in the main panel of your house. Current essentially all returns on the neutral to secondary of the pole xformer. The Earth is much higher impedance than the path back to the pole. Even during a ground fault event the current returns on the ground (technically EGC) to the bond point in the panel, and then from there back to the secondary of the utility pole.
Grounding to earth itself mainly serves to hold the potential of your house near that of the pole.
This is the weirdest rationalization of three-phase power I've ever read. By your reasoning and disregarding cos phi issues, monophase power is also constant-zero power, since it's two wires anyway and one is always the opposite of the other.
The best explanation of why three I was ever given hinged on "it's the number-of-phases argmin for the needed volume of wiring".
Three phase power is extraordinarily useful for electric motors. Mount three electromagnets radially and wire each up to a different phase, and you get a rotating magnetic field that spins on the axis. Electric generators produce three-phase power pretty naturally through the inverse process of spinning a magnet through the resistance provided by three groups of windings.
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.
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.
To clarify, do you mean Tesla the person or Tesla the car company? I figure the answer should probably be obvious to me, but I'm not an electronics person and it's not.
You are right. Three-phase needs less copper wire for the same amount of power delivery, which is the real reason everyone uses it. It needs less copper because it never has "dead time" where the copper isn't delivering power (hence the desire for constant instantaneous power).
I tried to word my explanation as accurately as I could, but I had to leave out a lot of tricky details for people who aren't electrical engineers. You have to be careful not to mix up regular averages, RMS averages, and instantaneous values when you deal with AC. If you get them wrong, you come to incorrect conclusions, such as the idea that single-phase electricity has zero power. The average voltage is indeed zero, but you can't use regular averages when you calculate power delivery, only instantaneous voltage differences and currents. You get RMS averages when you integrate those instantaneous values over time, and that brings in the the cos(phi) issues you mention.
This isn't correct for most residential installations in the U.S. for most of those, they have split phase power (https://en.wikipedia.org/wiki/Split-phase_electric_power) provided by a center tap transformer. This produces a neutral and two hot wires, each 180 deg out of phase from each other. Hook either hot to a neutral, and you get 120V, hook one hot to another and you get 240V.
In some places though, (I know it's common in New York, and also in a lot of datacenters), they do something like you describe, and hook 2 phases of a 3 phase system together. Since these are only 120 deg out of phase from each other instead of 180 in the split-phase system, you get less voltage, specifically 208V.
I recently watched this youtube video[1] that explains three-phase power using water, and it was pretty useful and clear in explaining this to a layman like me.
To use an analogy of water in hoses, there are three tubes in a power circuit. There's a "hot" one, colored red or black. There's a "neutral" one, colored white. And there's a "ground" one, colored transparent or green.
Under normal circumstances, the "hot" and "neutral" forms a continuous loop. But the pump that moves the water is connected to the "hot" hose. It alternates between pushing water out and sucking it back in. The "neutral" hose comes back from whatever is using the water and empties out into the tank that the pump uses as its water supply.
As long as the loop stays intact, anything the pump pushes out to hot will come back around in the neutral and get dumped back into the tank. Anything the pump sucks out of the hot will come back around from the neutral and get sucked out of the tank.
If you cut the neutral hose, the hot hose can still work, but only if you have a water reservoir at the other end big enough to accommodate a complete cycle of pushing and pulling. The pump operator doesn't like this too much, because it makes them reliant on customers to keep their water tanks in good condition, and if one gets damaged out there, the pump can't work as efficiently, and it could get damaged too. It's just safer for them to provide a second hose back to their own water tank.
But if you cut the hot hose, breaking the loop, neutral's got nothing. The water in it just sits there. This is where the ground hose comes in. It is also shoved into the water tank at one end, same as neutral. It's sole purpose is to complete a loop back to the water tank in case the regular loop fails, so that water doesn't spray too far or let air get into the pump. Ground is the emergency backup return path.
Connecting electrical wires to a ground rod pounded deep into the earth is like sticking the loose ends of your hoses in the ocean. You can pull as much water out of it as you need, and dump as much into it as you need. Sea level stays the same.
Three phase power distribution is also more economical in terms of wiring. You need less conductor to distribute the same amount of power compared to running using two phase.
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.
Expanding on this: because the neutral current is close to zero, the conductor for the neutral current has looser requirements on its impedance. With perfectly balanced phases the neutral conductor can be eliminated, saving money and material. In practise, the Earth itself gets used as the neutral conductor. This is why one sees three wires in transmission lines and not four.
Incidentally, the closely spaced multiple wires within each conductor of an electrical transmission line, typically held apart by spacers, act to reduce the inductance of the transmission line, which reduces losses. The little "dumbbells" which are on each side of each tower, are vibration dampers to reduce metal fatigue.
Typical large generators will have between 12 and 24ph (in multiples of three). They're split out in triplets 120 degrees apart. If you see 12+ phases out in the wild, you're probably close to a power plant.
That is single phase. The "hot" (or "live") wire has a nonzero voltage relative to ground, and the neutral wire is usually around the same voltage as ground (do not count on this).
The one-way plug ensures that the "hot" voltage stays in the wall when the device isn't on, so if you shove your wand into a toaster that's off you won't get electrocuted. Devices are always connected to neutral, and the switch connects them to hot.
Fun fact - the reason outlets in new construction are installed upside down (ground prong on top) is that the groudn prong can stop this from happening if something falls on it:
UK has 240v for everything which may explain the insulation. Has been the standard about as long as I can remember - so back to the 70s.
Someone put a lot of thought into the design. Ground at top to prevent accidents like you show. Ground pin is longer. Insulation covers enough of the pins that live and neutral disconnect before conductor is exposed from socket. Both will be fully disconnected before earth disconnects.
It's not just new constructions, ground pin on the top has been the "correct" orientation for a long time. They've been installed "upside down" this whole time but that's what stuck. It's not in the NEC and while there was a suggestion to put the ground pin up, that has never been required by code and most people think that having the ground pin down looks correct.
If you actually look at a NEMA 5 outlet with the ground pin compared to old ungrounded polarized NEMA 1 outlets the NEMA 5 outlet is rotated 180 degrees. The larger neutral slot is on the right on old outlets and with the ground pin down on a NEMA 5 outlet the neutral is on the left.
It's not just for people dropping coins or paper clips on it though. Some outlet covers are metal and if the screw is loose or damaged that's basically guaranteed to short out if something is plugged in with the ground pin on the bottom. Another common thing is people using a tape measure along a wall, it's so thin that if there's a small gap it could shock someone using it or if you're lucky just short against the neutral.
> As several people have pointed out, this isn't quite how it works in real life.
“Isn’t quite how it works” is a gross understatement. I apologize, but while there’s some correct facts, the entire narrative you spun clearly shows you don’t have the first clue what you are talking about. I really want to be as polite as possible, but what did you expect to accomplish by posting this?
A good book on this and related subjects is
Infrastructure: The Book of Everything for the Industrial Landscape by Brian Hayes. Published in 2006 so almost certainly out of print, but probably easy enough to get on Amazon or similar.
Thanks to both of you. It does seem to be a great book! I've requested it (well, the older version) from my library. Apropos this article: http://industrial-landscape.com/#/18
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.
I was looking at the transmission lines one day and was curious about why there are always 4 wires. Basically, 3 lines carry equal voltage phased 120 degrees apart from one another. This kind of power is easily generated from 3 phase power generators at the power plant. The 4th wire is a common return for all three wires. It is normally smaller than any single load wire because, if the power is distributed evenly, no load is carried on it.
The second part of the system, is that, normally, no one customer will use more than one of the three load lines. That is why most houses only have one transformer on the pole out side their house. The power company makes sure they balance connections evenly within a given area. If they do this properly, the common 4th wire has no load on it.
Some buildings do use all three phases, but they would be running large industrial machines that benefit from having that type of power.
I tried to find the Wikipedia article that covered all this, but can't seem to locate it specifically.
Its not so much that you have to balance the load in a given area. You must balance the load beyond breakers as much as possible. If the load becomes too far out of balance, the much larger feeder breakers at the substations will trip to protect the grid upstream from the imbalance.
I think New Zealand is the same as Australia with 5 wires: the 3 phases, neutral (the central return wire) and earth. Grabbing a random location in Auckland off Street View shows 5 wires:
That just seems odd to me to have a wire for earth... carried above the earth. I can understand having earth wires in houses made of concrete and wood since they have to get to the earth through those materials, but what makes a common earth ground better than just lots of many grounding points? All that wire has got to get expensive.
The point of an earth ground is to dissipate the accumulation of static built up. Ground is not connected to the power supply so there is nothing to return to the power company. The earth is the best place for it.
That's a higher voltage power line (in the low kV range) with just the three phases. They're relying on the load being approximately distributed between the three in the downstream distribution network to obviate the need for any return wire. If you move forward one step on that road you will see the next pole has a lower set of wires which will be at 230/240 volts. On these it looks like there are four wires, they're probably doing without the earth wire in this rural area and just tying to earth periodically.
Your bottom picture also shows half of a snowshoe fiber slack storage location. They are used at almost every splice so the splice can be moved to the ground easily and placed into a splicing trailer. That fiber pictured is a strand and lash construction where a high strength steel wire is placed and then the fiber is basically tied to it. We have stopped using any of it in favor of ADSS fiber which means all dielectric self supporting. We can place it in the power space and avoid dealing with the communications space problems.
> a snowshoe fiber slack storage. They are used at almost every splice so the splice can be moved to the ground easily and placed into a splicing trailer.
Interesting, thanks for pointing out how it's called and what's the purpose of it. I saw it around, but had no idea what it's for :)
I noticed though, that for example Optimum fiber network is using it, while Verizon one does not.
In Australia we have a life extension program for hardwood poles which slides a steel formed sock/support down the side to stabilise it for many a year more after a hard life.
We had some issues with corrosive dog wee. Tar treatment sometimes works. Also steel collars to keep possums off the top structure.
In Europe there are other platforms above the transform and wire complex for bird nests. Storks, cranes all above the risky bit.
Aussie poles are made from wood which is harder than nails. Unbelievably strong stuff which years of soaking in very nasty chemicals defends from termites which are ubiquitous.
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 architectural historian) leaned over and said "anachronistic: that wasn't introduced until the 1950s" which goes to show fanaticism over street furniture and the poles is deep deep down...
There is a transmission system in India rated for something over a million volts. The last time I looked it was only carrying about 800kV, though. Just why this was so was not explained. IIRC it was on the Wikipedia article on transmission grids.
IIRC, my college power professor said that Russian transmission lines carried 1 million volts, whereas US transmission lines only carry half a million volts.
We do have plenty of 500 KV (all over Louisiana and Arkansas for example), but a good bit of 765 as well. It's very costly to get right-of-way and the bigger the installation the more right-of-way you need.
As I understand it one of the largest concerns in AU are the wildfires damaging circuits connecting the disparate grids. There was some conversation about replacing some of the network poles with fire resistant poles in order to try and avoid the high number of outages caused by fires during the dry season.
I'd be interested to know how that project went, and if it was successful.
Not so much bushfires damaging electrical infrastructure as electrical infrastructure starting fires. A large portion of Victoria's worst day of bushfire was sparked by a faulty power line and the electricity distribution network (22kV and below) is responsible for a good portion of fire starts, especially those lines that utilise a single wire with an earth return (SWER). The recommendations of the Royal Commission into the Black Saturday fires in regard to the electricity network are available at http://royalcommission.vic.gov.au/Commission-Reports/Final-R... and contain a whole lot of background information. Suffice to say that the recommendation (27) of the wholesale burying of thousands of kilometres of SWER line at the cost of billions of dollars haven't gone far.
Fire resistance is one of those complicated things. Its not necessarily true that wooden poles are a worse risk than other ones. Steel loses structural integrity under fire heat (ok.. please do not talk about jet fuel and planes...) so for some forms of fire, a wooden pole can survive.
I think most references to fire risk with electricity distribution are actually arguing for underground wiring in the longer term.
Dry season is very much a northern part of australia concern (for now. the dry\wet cycle is moving south quite rapidly). The summer (which is the wet in the north) is when the bush fires happen.
Insulation is expensive. Furthermore, with AC you have to worry about the impedance of whatever you use as insulation. Basically the whole wire starts to act as a big capacitor, leaching power. (1)
I found some cost estimates: "The estimated cost for constructing underground transmission lines ranges from 4 to 14 times more expensive than overhead lines of the same voltage and same distance. A typical new 69 kV overhead single-circuit transmission line costs approximately $285,000 per mile as opposed to $1.5 million per mile for a new 69 kV underground line (without the terminals). A new 138 kV overhead line costs approximately $390,000 per mile as opposed to $2 million per mile for underground (without the terminals)." (2, page 17) Also, diagnosing and correcting faults is much easier above the ground than under, and you'd be surprised how often jackasses with backhoes take out underground infrastructure.
It is an order of magnitude more expensive to bury utility lines under ground, both in upfront costs and ongoing maintenance costs. This is due to the safety that has to be put in place to protect the wires, and the people who may dig into the wires while they are underground. Additionally making alterations to a power system due to a growing or changing residential power needs is much harder to do and takes longer when the power is routed under ground.
An individual pole is relatively fragile indeed, but they're stringed together with steel cables, so the whole assembly is pretty solid.
Source: Worked as a phone technician a while ago, climbed in these poles for a living. I hated climbing in "service poles" (individual poles not connected to the steel cable, used in cases where a house is far from the street), they'd wobble like crazy.
Most of Europe buried its LV power cabling decades ago. The answer is probably a mixture of "nobody bombed US cities", "no funding" and "lower population density". Although the latter doesn't apply to metro areas, obviously.
(Also, residential three phase power is fairly common except for the brits).
Wood rots and breaks. Burial has flood issues. The solution is to install better poles.
Most commonly, the poles are concrete with a square cross-section. Some are round concrete, spun while hardening to allow a hollow interior. Some are galvanized steel, with perhaps a decagonal cross section.
One near my house is about 2 feet thick, with a label that says 50,000 pounds.
Many of the easements for above ground utilities also contain provisions for underground utilities, so getting easements may be easier than you would think. However, having the easement, and having it be feasible to use are two different things. In my neighborhood, some sections have the utilities in line with the sidewalks and there is easy access; others have the utilities behind the homes, over many years many buildings have been built encroaching the easement. The encroaching buildings aren't legally there, but it would be messy to remove them to underground the utilities.
Also maintenance and access. I once had an underground power line to my apartment building fail, and it took the better part of the day for them to repair it. They had to tear up the parking lot in the process.
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.
Sort of related, but if anyone finds this topic interesting and is looking for software positions related to power systems engineering the startup I work for is hiring. We create 3 phase unbalanced distribution system simulation and optimization software to enable PV & battery integration by utilities.
What exactly does the company do and how do they do it? It is kind of unclear and the "Our Mission" section of the website is one of those generic PR sentences that doesn't actually explain anything about the business...
"The poles around here all carry ID numbers, and I imagine that back at the electric company there are giant books listing, for each pole ID number, where the pole is. Probably they computerized this back in the seventies, and the books are moldering in a closet somewhere."
Pretty much... I did data entry for 10 weeks in 2006 putting scanned records of wayleaves into a GIS system for Central Networks (a UK based electricity infrastructure company). Basically they had a record of every single pole, pylon etc, and a record of the legal agreement to access the pole for maintenance (a huge number are on private land, like in a farmer's field or your back garden or an office parking lot). All these records had been input into a GIS system by taking the (very) rough map reference and the pole number, putting that into structured fields, andthen everything else was just scanned documents - my work was part of the upgrading of that (which had been done years before) to completely structured data and a very accurate placement on the map.
For legal reasons a lot of the original documents are still kept somewhere. Typically these documents outline both the placement, access arrangement and any payments (which may be ongoing) made to ensure access.
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..
> The cans are full of mineral oil, or sometimes vegetable oil! (Why are they full of oil? I don't know; I guess for insulation. But I could probably find out.)
Isn't it also to keep a pressurized environment in the can and prevent moisture leaking in, resulting in rust? I was reading up on these too recently. Oil is also used in large circuit breakers to extinguish electrical arcs.[1]
Transformer oil is there primary for cooling and secondary for corrosion resistance. When you see transformer burning, it's the oil inside. Larger transformers cycle oil through pipes visible outside.
In the Czech Republic (or at least in some parts) pole numbers and their positions are shared with emergency services. If you are disoriented, reading the number identifies your exact position. Works for railway crossings as well.
> As I discussed recently, some of those poles are a hundred years old, and the style of the ID tags has changed over that time:
Truly amazing craftsmanship, right there. Infrastructure that's backwards -and forwards - compatible. Unhackable, able to run for decades or centuries at a time.
Phone lines? Are line phones still so popular in Germany that it even requires network expansion? In my country copper lines are basically left to rot as line phones are being replaced by cell/IP phones rapidly. In some cases people living in remote areas were issued free cell phones, because it was cheaper than repairing old copper lines.
most household uses ... they want single-phase power!? In 1910, maybe.
Huh? In the USA all residential is single-phase. Although there's a center tapped transformer involved, which is what gets you both 120 V and 240 V from one phase. This arrangement is called "split-phase": https://en.wikipedia.org/wiki/Split-phase_electric_power#Nor...
Name one "household use" in the USA (which is where the author lives) that doesn't use single-phase power? I'll give you a head start, I once lived in an apartment building that used 120V/208V for electric hot water heaters. But offhand I can't think of anything else.
It is strange though, that residential three phase is so uncommon there, especially when the single phase voltage is only 110, further sacrificing efficiency for high power applications.
PCBs were used because they are really good thermal conductors, which is the same property desired of cooking oil for frying. In recent years, thieves in Kenya (which has yet to replace PCBs with something less toxic) have been vandalizing [3] transformers and selling the oil to street vendors, which has the twin effects of destroying the fragile electrical infrastructure and poisoning the neighborhood.
[1] https://en.wikipedia.org/wiki/Pollution_of_the_Hudson_River [2] https://www.epa.gov/ge-housatonic/understanding-pcb-risks-ge... [3] https://www.reuters.com/article/kenya-electricity/thieves-fr...