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Transformers: Devices for Energy Transfer Between Circuits

A transformer transfers electrical energy from one circuit to another without a metallic connection.
A varying current in the primary coil produces a varying magnetic flux in the core, which induces an electromotive force (EMF) in the secondary coil.
Transformers are used to change AC voltage levels, provide galvanic isolation between circuits, and couple stages of signal-processing circuits.
Since the invention of the first transformer in 1885, they have become essential for the transmission, distribution, and utilization of AC electric power.
An ideal transformer is linear, lossless, and perfectly coupled with infinitely high core magnetic permeability and winding inductance.
Real transformers have core losses, winding resistances and inductances, parasitic capacitance, and leakage flux.
Leakage flux results in inferior voltage regulation, causing the secondary voltage not to be directly proportional to the primary voltage.
Transformer equivalent circuits incorporate an ideal transformer and winding joule losses, leakage reactances, and core loss and reactance.
Transformers are vulnerable to insulation failure due to transient voltages with high-frequency components.
Transformer energy losses are dominated by winding and core losses, with hysteresis and eddy current losses constant at all load levels.
Designing energy-efficient transformers requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire.
Transformers can have core form or shell form designs, with laminated steel cores made of high permeability silicon steel and constructed by stacking layers of thin steel laminations.Transformers: Types, Construction, and Applications
Transformers are used to transfer electrical energy from one circuit to another through electromagnetic induction.
To prevent harmless inrush currents, protection devices such as fuses must be selected.
Geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices on transformers connected to long, overhead power transmission lines.
Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous metal alloy.
Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz.
Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level.
The main disadvantages of toroidal transformers are higher cost and limited power capacity.
Air-core transformers are unsuitable for use in power distribution, but are frequently employed in radio-frequency applications.
Large transformers are cooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of these.
Transformers may be classified based on their applications, including electric power transmission, electronic devices, signal and audio, isolation, and resonant transformers.
Electromagnetic induction, the principle of operation of transformers, was discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832.
The first type of transformer to see wide use was the induction coil, invented by Rev. Nicholas Callan of Maynooth College, Ireland in 1836.The Invention and Development of Transformers
Before the 1880s, AC power transmission was done through inefficient series circuits with open-core transformers.
In 1885, Hungarian engineers Károly Zipernowsky, Ottó Bláthy, and Miksa Déri invented closed-core transformers, which were more efficient and reliable for regulating voltage.
The first closed-core transformers were shipped by the Ganz Works in Hungary in September 1884 and were 3.4 times more efficient than open-core transformers.
The ZBD patents for closed-core transformers also included innovations for parallel-connected utilization loads and high turns ratio transformers, making it feasible to provide electric power for lighting in homes, businesses, and public spaces.
The ZBD engineers also invented lamination of electromagnetic cores in early 1885 to eliminate eddy current losses.
The ZBD engineers popularized the word "transformer" to describe a device for altering the EMF of an electric current.
In 1886, the ZBD engineers designed the world's first power station that used AC generators to power a parallel-connected common electrical network, the Rome-Cerchi power plant.
George Westinghouse bought Gaulard and Gibbs' patents in 1885 but had to develop alternative designs for the US market due to Edison Electric Light Company's option on the ZBD patents.
William Stanley developed an induction coil design with soft iron cores and adjustable gaps, which was used commercially in the US in 1886.
Westinghouse, Stanley, and associates developed a low-cost design for closed-core transformers with a stack of thin "E-shaped" iron plates insulated by thin sheets of paper or other insulating material.
In 1889, Russian-born engineer Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer in Germany.
In 1891, Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for producing very high voltages at high frequency.