AC Transformers

Chronology

A transformer is a device that changes the amount of voltage (V) and alternating current (I) between the input windings and the output windings.   The power (P) remains the same at both input and output sides of the transformer.   Since P = V x I on both sides (ignoring small losses), then

Thus, a low voltage and high current is "transformed" into a high voltage and low current and vice-versa.   Because losses along a wire are proportional to the current, they will be reduced over long distances by transmission with high voltages and low current.   At the power destination (homes, factories, offices), the voltage is reduced and the current is increased for safety and operating ease.   Transformers CANNOT be used for direct current, which is why alternating current generators that produce alternating current are more efficient than direct current generators for transmitting power over long distances.

To 1790

1790-1799

1800-1809

1810-1819

1820-1829

In 1820, the Danish scientist, H. C. Oersted discoveres the existence of a magnetic field surrounding an electric current.   From this knowledge, D. F. J. Arago in 1820 and William Sturgeon in 1825 produce the first laboratory model electromagnets and Michael Faraday, a British scientist, demonstrates the principle of an electric motor. ^{Singer 179,180,231}: Iron wound with wire carrying an electric current made the iron into a magnet.   The power for the electromagnetics comes from batteries.   Joseph Henry sees a demonstration of Sturgeon's battery in New York City in 1826 and publishes a paper on electromagnetism in 1831.   He then spends several years developing more powerful electromagnetics that are used commercially.

1830-1839

In 1831, the British scientist, Michael Faraday, discovers the principle of magnetic induction:   A magnet moving in the vicinity of an fixed electrical circuit produces a current in it.   Alternately, the circuit moving in the presence of a fixed magnet produces a current in the circuit.   In the same year, he also demonstrates a transformer, in which parts of a winding can induce currents in other parts of the same winding.   However, he uses it only to demonstrate magnetic induction. ^{Singer 179,198} In the same year, Joseph Henry, an American scientist, independently of Faraday demonstrates the principle of electrical induction by using it to ring a bell.   The bell is operated remotely by means of an electrical circuit powered by a battery. ^{Carruth 185}   However, Faraday publishes his results first, so he is credited with the discovery.

1840-1849

1850-1859

1860-1869

1870-1879

1880-1889

Lucien Gaulard and John Dixon Gibbs invent a device called a "secondary generator" in London in 1881.   It is the first practical transformer.   They sell their patent to the Westinghouse Corp., which is looking for a practical way to decrease high-voltage transmitted alternating current to make it safe for factories and homes.   They exhibit the invention in Turin in 1884, where it is adopted for its electric lighting system.   It uses an open iron core, which is later abandoned in favour of a more efficient circular core with a closed magnetic path. ^{Wiki n.p.}   It does not work well, but will serve as a model for an improved 1885 Westinghouse transformer.

William Stanley, an engineer for Westinghouse, builds the first practical transformer in 1885 following the Westinghouse purchase of the Gaulard and Gibbs's patents.   The core is made from interlocking E-shaped iron plates.   This design will be used commercially in 1886. ^{Wiki n.p.}

1890-1899

1900-1909

1910-1919

1920-1929

1930-1939

1940-1949

1950-1959

1960-1969

1970-1979

1980-1989

1990-1999