Edision and Westinghouse go to war
Everyone probably knows that the electricity supply we get from our wall outlets is Alternating Current (AC), and not Direct Current (DC). Why is this? Well, there are certain crucial advantages to using AC to distribute electricity from power stations, but the decision to use AC and not DC actually has quite an interesting history.
Thomas Edison, the well known inventor and businessman, developed a system of distributing power using DC, and had a number of patents for this system. The state of New York adopted his DC power distribution system, and it made Edison’s company a lot of money. In the early 1880s, this was the preferred system.
However, by the late 1880s an efficient transformer had been developed in Europe, by engineers at the Ganz Works in Hungary. A transformer changes the voltage, it can either increase or decrease a voltage (a step-up or a step-down transformer). However, a transformer works using the principle of electromagnetic induction, and this requires an alternating current. It does not work with a direct current. Once the ability to change voltages using an efficient transformer had been developed, it lay the way open for AC’s strongest advantage, reducing power losses in transmitting cables. This is where George Westinghouse enters the story. He saw a business opportunity to rival Edison, and in 1886 he hired William Stanley Jr. to work on an AC distribution system utilising step-up and step-down transformers. Westinghouse also licensed the 1887 US Patents of Nikola Tesla’s invention of the AC inductor motor, and hired Tesla as a consultant. Tesla had come to the United States from Serbia in 1884 to work for Edison, so Westinghouse hiring him as a consultant would not have gone unnoticed by Edison!
Reducing power losses in transmission cables
Any electricity cable used for distributing power has a certain resistance. This resistance depends on the material being used (which is usually copper), the length of the cable and the cross-sectional area of the cable. For a cable with a certain resistance R, the power lost in the cable as electricity flows along it is given by the formula where is the current. By transmitting the electricity at a high voltage, the current can be kept low, which keeps the power losses low.
Thus, a power station can send its electricity at a very high voltage (often 250,000 or even 400,000 Volts), and this voltage is reduced using transformers in several steps, finally coming into our houses from a local sub-station where it is converted down to 240V in Europe and most of the World (or 110V in North America). Transmitting at such high voltages keeps the power losses in the distribution cables down to acceptably low values, meaning power stations can be located dozens of kilometres from the homes and factories they are supplying. In contrast, with Edison’s DC system, power generators needed to be within 1.6km (1 mile) of the devices they were supplying, meaning every community needed to have its own generating facility! Edison tried to argue that this was more “democratic”, as it would keep power generation out of the hands of big businesses.
Most domestic appliances either don’t care whether they use AC or DC (examples would be a toaster, an oven, an electric fire), or they need to use DC (this tends to be small appliances like a radio, music system, clock, computer). For appliances needing to use DC, a device called a rectifier is used to convert the AC to DC. But, not only was the short distances DC could be distrbuted a problem for Edison’s system, one of the other problems was that different cables were needed for devices needing different voltages. In the 1880s the main devices requiring electricity were incadenscent light bulbs, which could operate quite well at 110V, and DC electric motors, which needed a higher voltage. Edison needed to supply both voltages separately, leading to at least twice as many cables. Converseley, with the AC system, voltages could be changed with transformers, so only one set of cables was needed to supply devices requiring different voltages.
Edison’s campaign to discredit AC
One of the more interesting chapters in this history is some of the things Edison did to try to win the AC/DC war. Edison had so much money to lose should AC be adopted as the preferred electricity distribution system that he mounted a concerted campaign to discredit AC. He spread disinformation on the dangers of AC, exaggerating or simply making up incidents of accidents with AC. He also started a series of demonstrations where he (or, more usually, a representative of his Company) would publicly kill an animal (usually a stray cat or dog) using AC, to show how lethal AC was. Of course, none of these demonstrations pointed out that DC was equally as lethal!
Possibly the most famous animal execution Edison’s Company undertook was that of a circus elephant called Topsy. Tospy had killed her trainer (who had apparently burnt her trunk using a lit cigar), and then trampled two other circus workers in the ensuing hubbub. The Forepaugh Circus Company deemed she was a danger and so arranged for her to be killed. They were going to hang her, but Edison stepped in and suggested electrocution as part of his on-going demonstrations of the dangers of AC electricity. Topsy was electrocuted in January 1903.
Despite being an opponent of capital punishment, Edison even went so far as to sponsor the development of the electric chair by Harold Brown which was adopted by the State of New York as their preferred method of killing people who had committed a crime punishable by death. The first executions of prisoners using electrocution started in 1890.
Ultimately Edison lost his battle. AC was adopted as the electricity distribution system throughout the World. It was one of the few business failures Thomas Edison suffered in his highly successful career.