Got it. That’s what we’ve been talking about.
Neat. Never heard of it. Do I ever encounter it? I can’t just call up Con Ed for that, right? Buy some [devices called?] to [whats the word?] to transform the signal? [devices called Transformers?–i know them as AC/DC things only.]
Got it. I’m going to go look up again the Edison-Westinghouse battles. (Wasn’t there an electrocuted elephant involved?)
Means: do the devices exist, if they do what are they called, and what is the technical word for such a conversion/transformation of the signal?
Also, of course, “did I ever encounter them” means: what the heck uses polyphase power?
3 phase power, poly phase, is used in the business and industrial world. Motors over 1 Hp are often three phase. A single phase motor requires 3 wires, and a capacitor, require more amps on the single leg, and are physically larger. A 3 phase motor requires 4 wires but require less amps per leg and are physically smaller.
The 60 cycles on single phase or 3 phase means that the time of 0 amps, volts, or power is only for 1/60 second, not enough to slow a motor or heater down. Put a strobe light on a single phase motor and it will appear to run at a constant speed.
You encounter it all the time and don’t realize it.
Most power in the U.S. (and most other parts of the world) is generated using 3 phase polyphase power.
Let’s say you are using single phase power, and you have 3 areas that you need to give power to. You run 3 sets of wires out and 3 sets of wires back, because electricity has to make a complete circuit out and back to work. Now, let’s do the same thing with 3 phase power. You run three sets of wires out, but you tie all three return wires together and run a single wire back. And here’s the trick. If you add 3 sine waves together that are each 120 degrees out of phase with each other, they add up to zero. That means that if everything is perfectly balanced, you have no current at all flowing through that single return wire, and the wire doesn’t need to be there. In the real world, your loads will rarely be perfectly balanced, but you can use a fairly small return wire, instead of needing 3 separate return wires or one really big return wire.
So that’s exactly what the power company does. Power is generated and sent to substations using 3 phase. Look at those big transmission line towers. They usually have 3 wires (or 3 pairs of wires) hanging from them, with one smaller wire on top (a protective ground to help shunt lighting strikes to ground instead of having them go down the wires). When the electricity gets to the substation for your neighborhood, then it is typically split into 3 individual phases that are run to separate houses. So for each circuit around your neighborhood you still need two wires (one out and one return), but from the substation back to the generator you only need 3 big wires and one small one.
So the power in your house looks to you like it is just a single phase system, but in reality it’s one phase of a 3 phase system. When it gets to your house, your house plus a couple of others (typically) are fed from a single split phase transformer. There are two “hot” lines from either end of the transformer coil, and one “neutral” line from the middle of the coil (hence, “split” transformer). From either line to neutral is 120 volts, and from line to line is 240 volts.
In some areas, all three phase wires are run around the neighborhoods, and each house gets 2 phases out of the 3 phase system. You can easily tell if you have one of these, because in this case the line to neutral voltage is still 120 volts just like above, but the line to line voltage is 208 instead of 240. This means that it takes your oven longer to heat up and your clothes dryer longer to dry clothes. This type of power feed is fairly rare in the U.S. but is still in use in parts of NYC and some other big cities, and on a few older rural systems here and there.
Larger business buildings are often fed from 3 phase power. When you order a big business copier/printer (one of those big floor standing models) you often have to specify whether it is to be powered from 240 or 208. Sometimes they just move a wire inside the copier. Other times they actually install different power transformers in the copier.
Some ovens and dryers often have different heating elements available for use with 208 systems. These are often installed in large apartment buildings that are fed from 3 phase.
Sure you can. But they’ll charge you a lot of money for it. 
Wrong. Per Merriam-Webster dictionary 
Plus, the term was used regularly when I went through some electronics courses (both US Army Artillery computer/radar plus interfacing them training/school for repair of targeting/coordinating-fire systems, and college-based general stuff as well), long ago.
Not quite. A “transformer” is the traditional device to transform AC of one voltage to AC of a different voltage. Transformers have no role in DC.
Tagging on to engineer_comp_geek’s superb post …
Within the context of home power delivery the trash-can sized gray thingies you see hanging on most residential power poles are transformers. They take the voltage running along the wires between poles, typically 6 thousand to 20 thousand volts, and convert that to 120 and/or 240 volts for use in houses. Bigger high capacity transformers do similar duty for powering large buildings or factories, typically supplying 240 & 480 volts to those buildings.
The traditional device for converting AC to DC is called a “rectifier”.
Late addition missed edit window:
A possible source of your confusion is that many low-power consumer products like phones, and much of the battery or plugin-able consumer electronics of the 70s through 90s, were designed to consume DC power at low voltage, typically 3, 6, 9, or 12 volts depending on the specific device. And they were supplied with a power cord which included a mysterious block or “brick” embedded along the cord or at the plug end. These last were / are commonly called a “wall-wart”. The brick or wall-wart converted 110 volt AC to low voltage DC.
And folks tended to call them “transformers” although inside they actually used a transformer for the AC voltage change, followed by a rectifier to convert low voltage AC to DC.
Nowadays totally different technology is used to make the same conversion. Which is why wall-warts or bricks made since about 2005 are much smaller & no longer very heavy.
The punning, it hertz.
Not sure if this is exactly on your question, but it’s relevant: Motors are an inductive load, which means that they cause the sort of phase shift we’re talking about in one direction, leading to the above-mentioned inefficiencies. But you can correct for that by putting capacitors in the circuit, shifting the phase back the other way. Put in the right amount of capacitors, and you shift it back to exactly zero, and so you don’t have these problems at all. For home users, the power company usually doesn’t care about this, since it makes a very small difference (most loads in a house are resistive, like light bulbs, anyway), but for industrial users, they’ll often require that the user put in the power-correction capacitors, or charge them a lot more on their bill.
I clothe myself in garbage.
Industrial customers with large power demands often have a much higher voltage primary interconnect with their utility - 4160 V or 26 kV, for example - and step down that power themselves within their facility.
Page 1991 of my Shorter OED says otherwise.
Now then - 60 cycles - is that 60 hertz? I had some American guests on a cruise ship the other day - a European cruise ship. They told me when they were in Europe (not on the ship) their appliances didn’t work properly even though they had the right adaptors. Is this because mainland Europe operates on 50 hertz? Their stuff worked fine on board the ship - a European ship (not English) - so who loses out there or how do they cope on the ship with 50 and 60 hertz applicances? Or have I completely not grasped this hertzage thing?
Hertz (cycles) is a measure of frequency of electromagnetic waves, not potential, current, or resistance used for measuring electrical power. It’s relevant to wireless reception.
For example, AM radio station frequencies are measured in kilohertz (kilo cycles) and FM stations and over-the-air TV are in megahertz.
Yes, 60 Hertz (abbreviated Hz) is 60 cycles per second. The unit is named after Heinrich Hertz.
The standard outlet in the U.S. is 120 volts, 60 Hz. Most of Europe is 240 volts, 50 Hz. So not only is the frequency different, but so is the voltage. If I recall correctly, Japan is 100 volts with half of the country at 50 Hz and the other half at 60 Hz.
Most devices aren’t too picky about the frequency and can work with either one, but a lot of devices can’t handle the differing voltages. Many devices can be damaged if plugged into the wrong voltage outlet. There are a few that can be damaged by the frequency being off, but not many. Usually it’s the voltage that kills the device, and if the device isn’t designed to handle it, the voltage difference can literally make the device catch fire or explode.
Check the input range of your device before trying to connect it to a different type of outlet. If your laptop AC adapter says something like 100 to 240 volts, 50 or 60 Hz (very common for a laptop these days) then you can use it in the U.S. or Europe with just a simple plug adapter. Most USB type phone / tablet chargers will also work over a wide voltage range (typically 100 to 240 volts).
The wrong frequency won’t usually damage a device, but it can cause it to malfunction. Some motors have their speed determined by the frequency of their power supply, and so an American device with a motor might run a bit slow in a European outlet. Clocks are often based on the frequency, so you definitely shouldn’t trust an American alarm clock in Europe, or vice-versa.
How many clocks these days actually keep time off the line, vs. having a quartz timekeeping element? In 2011 the U.S. talked about ditching the precise regulation of frequency. I’m not really sure if they actually did it and what the effects were; I can’t find any more recent articles.
BTW, for all those edjucatin’ me, the view five yards from the back entrance to my apt. building. Hence the questions, and more to come. Like, what the hell am I looking at?
The piping and ducts are also quite beautiful.
Let it be known that is my first iPhone pan-o-rama.
That’s a substation. High voltages are more efficient for transferring power over long distances, but they’re also more dangerous and require more insulation. So the grid includes several different voltage levels, for different scales. At every point where you change voltages, you need transformers. The last transformer before your house is usually a thing about the size of a garbage can stuck on one of the utility poles near your house. The transformer before that is at a substation like the one outside your building.
Hertz=cycles.
Cruise ships often cater Americans. They may operate on 60 hertz.