Whether we suspect it or not, we are already pretty familiar with alternating current: This form of electrical energy is what powers our houses and appliances, our televisions and lights, our sounds and images.
Unlike direct current, which flows in only one direction and we use to charge batteries and supply large amounts of power, alternating current periodically reverses direction in a form that follows a sine wave. In order for the power to be transmitted through power lines at high voltage and efficiently, electrical energy is distributed as alternating current while a transformer can be used to increase or decrease AC voltage. The main advantage? It reduces the energy lost as heat due to resistance of the wire, plus the remaining is transformed to a lower, safer, voltage for use (because power transmitted at a higher voltage requires less loss-producing current than for the same power at a lower voltage. It also doesn’t need as much insulation and is generally safer to work with.)
Most electric power is generated at 50 or 60 Hertz. The frequency of the system depends on the country, some like Japan have a mixture of 50 Hz and 60 Hz supplies. This lower frequency can have advantages for railways and their motors, but also produces noticeable flickers in arc lamps and incandescent light bulbs. Some European rail systems still use 16.7 Hz power, for example Austria, Norway, Germany and Sweden. On the other end, 400 Hz can be used for the military industry, marine, aircraft, and spacecraft applications, mostly off-shore; while computer mainframe systems were often powered by 400 Hz or 415 Hz. All in all, we see values of 200 V (Japan), 208 V, 240 V (North America), 380 V, 400 V or 415 V (Europe), and generally 50 Hz or 60 Hz.
A somewhat unexpected use of alternating current is also to transmit information, for example using telephones and cable television. Plain old telephone service (1876 until 1988) signals have a frequency of about 3 kHz, close to the baseband audio frequency, while television shows similar to the electromagnetic wave frequencies often used to transmit information over the air.
The History of Alternating Current
The first-ever alternator that produced AC was based on Michael Faraday‘s principles. A dynamo electric generator, it was created by Hippolyte Pixii (a French instruments maker) in 1832 and included a commutator to produce direct current, which was more popular then. In 1855, Guillaume Duchenne, who developed electrotherapy, announced that AC was superior to direct current – albeit for electrotherapeutic triggering of muscle contractions, which was ‘his thing’. In the 1870, the Hungarian Ganz Works company began work in AC technology, and in the 1880s it was Sebastian Ziani de Ferranti, Lucien Gaulard, and Galileo Ferraris who paved the way for electric lighting. In Austria-Hungary, it was AC systems that used arc and incandescent lamps, generators, and other equipment.
Ganz factory is at the center of AC development of the time. In 1884, the engineers Károly Zipernowsky, Ottó Bláthy and Miksa Déri (ZBD) filed patent applications for novel transformers (later called ZBD transformers) with closed magnetic circuits where copper windings were either wound around a ring core of iron wires or else surrounded by a core of iron wires. One of its innovations: the magnetic flux traveled almost entirely within the confines of the iron core, with no intentional path through air, making these new transformers 3.4 times more efficient than the open-core bipolar devices of Gaulard and Gibbs.
Because of how good these systems were distributing electricity efficiently over long distances, AC power systems was adopted rapidly after 1886. In 1886, ZBD designed the world’s first power station which used AC generators to power the steam-powered Rome-Cerchi power plant electrical network. As soon as 1886, the Ganz Works electrified the whole of Rome, one of Europe’s main metropolis. In the meantime, Sebastian de Ferranti advanced his field in the UK, redesigning the AC system at the Grosvenor Gallery power station in 1886, the power station at Deptford in 1890 and converting then the first into an electrical substation. While in the US, William Stanley, Jr. figured out one of the first practical devices to transfer AC power efficiently between isolated circuits. His design, called an induction coil, was an early transformer. Adapting European designs for US entrepreneur George Westinghouse, who couldn’t wait to develop AC systems – which in turn triggered a push back in late 1887 by Edison who attempted to discredit alternating current as too dangerous. This is where the expression the “War of Currents” was born.
But when Galileo Ferraris and Nikola Tesla presented their functional AC motor, an electric motor driven by an alternating current, modern practical applications finally became a real possibility. Among the first hydroelectric alternating current power plants we find the Niagara Falls Adams Power Plant (1895), the San Antonio Canyon Generator (1892) and the first commercial three-phase power plant in the United States using alternating current–the hydroelectric Mill Creek No. 1 Hydroelectric Plant near Redlands, California.