Development history Faraday invented an "inductance ring" on August 29, 1831, which is called "Faraday induction coil". In fact, it is the first prototype transformer in the world. But Faraday only used it to demonstrate the principle of electromagnetic induction, and did not consider that it could have practical applications. Faraday induction coil, 1881, Lucien   Gaulard and John Dixon Gibbs   Dixon   Gibbs showed off a device called a "secondary hand generator" in London and sold the technology to Westinghouse,   This may be the first practical power transformer, but it is not the first one. In 1884, lucerne goral and John Dixon Gibbs demonstrated their equipment in Turin, Italy, where electric lighting was used. In the early stage, the linear core was used in the transformer, which was later replaced by the more effective ring core. William steinley, an engineer of Westinghouse, bought patents for transformers from George Westinghouse, Lucerne GOLAR and John Dixon Gibbs, and then built the first practical transformer in 1885. Later, the core of the transformer was made of e-type iron sheets, which was put into commercial use in 1886. The principle of transformer transformation was first discovered by Faraday, but it was not put into practice until 1880s. In the competition between DC and AC power output of power plant, the use of transformer is one of the advantages of AC power. The transformer can convert the electric energy into the form of high voltage and low current, and then convert it back. Therefore, the loss of electric energy in the transmission process is greatly reduced, and the economic transmission distance of electric energy is further. In this way, power plants can be built far away from electricity. Most of the world's electricity through a series of transformation, and finally to the user there. working principle   The transformer is composed of iron core (or magnetic core) and coil. The coil has two or more windings. The winding connected to the power supply is called primary coil, and the other windings are called secondary coil. It can transform AC voltage, current and impedance. The simplest core transformer consists of a core made of soft magnetic material and two coils with different turns on the core. The function of transformer core is to strengthen the magnetic coupling between two coils. In order to reduce eddy current and hysteresis loss, the core is made of coated silicon steel sheets; There is no electrical connection between the two coils. The coil is made of insulated copper wire (or aluminum wire). One coil connected with AC power is called primary coil (or primary coil), and the other coil connected with electrical appliance is called secondary coil (or secondary coil). The actual transformer is very complex, inevitably there are copper loss (coil resistance heating), iron loss (core heating) and magnetic flux leakage (magnetic induction line closed by air), etc. The condition of an ideal transformer is to ignore the leakage flux and the current of primary and secondary coilsIgnore the loss of the core, ignore the no-load current (secondary coil open circuit, current in the original coil). For example, the power transformer in full load operation (secondary coil output rated power) is close to the ideal transformer situation.