An interesting video below on three-phase power.
Interesting issues of independent invention of two-phase power by several parties and then independent invention of of three-phase power by Tesla and Dolivo-Dobrovolsky.
Tesla patented a six-wire three-phase system. Dolivo-Dobrovolsky actually built a better three-wire system.
Fascinating. Great explanation. Thanks.
It would be interesting to trace how the influence of AEG (Dolivo-Dobrovolsky) and Westinghouse (Tesla) affected the adoption of electrical power in the territories where they dominated the market. In central Europe (AEG), three phase 380 volt power is common in the home, with 220 volts between phases. House circuits are divided between phases to balance the load. Energy-hungry appliances such as ovens, stovetops, clothes dryers, and oil furnace burners are usually 3 phase devices.
In the U.S., domestic wiring is usually the 120/240 system with high energy devices wired across the rails for 240. I suspect this is a legacy of the original Westinghouse single- or two-phase system. While three-phase is near-universal for industrial power in the U.S., it is rare in domestic installations.
Somewhat off topic, but we live in a former mining area that had one of the early two phase power systems in the early 1900s, where the phases differed by 90 degrees instead of 180 like current US domestic wiring. Here’s a Wikipedia (yeah, I know) article.
The original generation building still exists, but all the equipment is long gone and it’s currently a business incubator for the local university
For really good articles on electricity I strongly recommend amasci (dot) com.
Using Charge (…as in coulombs) he builds an excellent foundation; wish I’d known of this guy as a teenager.
Bill Beaty “gets” it.
In Seattle, the historic Georgetown Steamplant still has it’s original contents, from 1907-1917 iirc. The DC output for city trolly lines is AC induction motors turning DC dynamos. Look close at the AC motors, and they’re 4-wire 2-phase! Yet they’re GE not Westinghouse. Also there’s a large water-cooled Scott Tee transformer, to convert three-phase into two (or the reverse.) I couldn’t tell whether the huge main AC generators are two phase or three. Maybe they’re like Niagara Falls, a 2-phase installation? It’s a very early coal-fired plant (well, early for being west of the Rockies.)
Still here!
Also, the above video has a problem: biased Tesla-bashing. (If Tesla’s history is right, then most of our grade-school Edison-centric history is wrong. K12 science teachers really hate this, and will fight to keep textbooks distorted and uncorrected.)
Actually Dolivo-Dobrovolsky was a DC designer for Germany’s Edison-AEG company. (They later removed the Edison name.) The AC part only happened when Oerklion’s Charles EL Brown came in with a transmission-line project. Brown wanted to prove the experts wrong about AC long-lines (they insisted that it was impossible, inefficient and worthless.) The 100-mile Frankfurt line stunned the experts by being above 75% efficient. Brown also wanted to test his own crazy proposal …transmission lines with bare conductors. The expert community declared those also impossible. Right then Brown encountered Tesla’s AC patents, and the accompanying belittling and rejection. So he decided to also make it a test of Tesla’s polyphase system.
Dolivo-Dobrovolsky was the designer, but soon began pretending to have invented it all. CEL Brown stepped up in public, and announced that the Frankfurt transmission line was due to the efforts of Nikola Tesla. Dolivo-Dobrovolsky publicly declared that the inventor of new devices was not the one to have the idea, and was not the one to patent them. Instead it was himself, the one to build industrial prototypes. (As if Tesla hadn’t been building huge 3-phase motors!) Tesla stepped in, saying he’d let the German patent courts decide the issue, also chastising DD for trying to invent things that had already been patented years before. Tesla didn’t know that DD well knew Tesla’s patents, and was dishonestly attempting to avoid having to pay to license the technology.
However, Tesla never patented any transmission lines. His docs only show a 3-phase line with two wires and buried ground-return plates as the third conductor, while his 3-phase patent shows a 6-wire line. So, Dolivo-Dobrovolsky genuinely invented the Wye 3-phase balanced line. Today everyone who believes that AC was invented by Edison, can insist that 3-phase was invented by Dolivo-Dobrovolsky in Germany, not by Tesla. In truth, Tesla invented the motors, the power grid, and “polyphase” including 3-phase 12-phase etc. (It was George Westinghouse who pushed for 2-phase everywhere. Tesla-bashers commonly use this to insist that Tesla somehow forgot to patent 3-phase. In reality Tesla believed that the more phases the better.)