Classification and development history of transformer
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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.
Main categories General transformer classification can be summarized as follows: 1. According to the number of phases: 1) single phase transformer: for single-phase load and three-phase transformer group. 2) Three phase transformer: used for voltage rise and drop of three-phase system. 2. According to the cooling mode: 1) dry type transformer: it relies on air convection for natural cooling or increased fan cooling, and is mostly used in high-rise buildings, high-speed toll stations, local lighting, electronic circuits and other small capacity transformers. 2) Oil immersed transformer: it depends on oil as cooling medium, such as oil immersed self cooling, oil immersed air cooling, oil immersed water cooling, forced oil circulation, etc. 3. According to the purpose: 1) power transformer: used for the voltage rise and fall of transmission and distribution system. 2) Instrument transformer: such as voltage transformer, current transformer, measuring instrument and relay protection device. 3) Test transformer: it can produce high voltage and conduct high voltage test on electrical equipment. 4) Special transformers: such as furnace transformer, rectifier transformer, regulating transformer, capacitive transformer, phase-shifting transformer, etc. 4. According to the winding form: 1) double winding transformer: used to connect two voltage levels in the power system. 2) Three winding transformer: generally used in power system regional substation, connecting three voltage levels. 3) Autotransformer: used to connect power systems with different voltages. It can also be used as common step-up or step-down transformer. 5. According to the form of iron core: 1) core transformer: used for high voltage power transformer. 2) Amorphous alloy transformer: amorphous alloy core transformer is a new type of magnetic conductive material, with no-load current reduced by about 80%. It is an ideal distribution transformer with energy saving effect, especially suitable for rural power grid and developing areas with low load rate. 3) Shell type transformer: special transformer for high current, such as furnace transformer and welding transformer; Or for electronic instruments and television, radio and other power transformers.