Transformer
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This article is about the electrical device. For the toy line franchi, e Transformers. For other us, e Transformer (disambiguation).
Pole-mounted distribution transformer with center-tapped condary winding. This type of transformer is commonly ud in the United States to provide 120/240 volt "split-pha" power for residential and light commercial u. Note that the center "neutral" terminal is grounded to the transformer "tank", and a grounded conductor (right) is ud for one leg of the primary feeder.
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A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the condary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the condary winding. This effect is called mutual induction.
If a load is connected to the condary, an electric current will flow in the condary winding and electrical energy will be transferred from the primary circuit through the trans
former to the load. In an ideal transformer, the induced voltage in the condary winding (Vs) is in proportion to the primary voltage (Vp), and is given by the ratio of the number of turns in the condary (Ns) to the number of turns in the primary (Np关于分手的歌真空包装保质期) as follows:
By appropriate lection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np.
In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons ud to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electr
onic circuits, transformers are still found in nearly all electronic devices designed for houhold ("mains") voltage. Transformers are esntial for high-voltage electric power transmission, which makes long-distance transmission economically practical.
Contents [hide] ∙ 1 History o 1.1 Discovery o 1.2 Induction coils o 1.3 Clod-core transformers and the introduction of parallel connection o 1.4 Other early transformers ∙ 2 Basic principles o 2.1 Induction law o 2.2 Ideal power equation o 2.3 Detailed operation ∙ 3 Practical considerations o 3.1 Leakage flux o 3.2 Effect of frequency o 3.3 Energy loss o 3.4 Dot convention ∙ 4 Equivalent circuit ∙ 5 Types o 5.1 Autotransformer o 5.2 Polypha transformers o 5.3 Leakage transformers o 5.4 Resonant transformers o 5.5 Audio transformers李白的家乡在哪里 英文文献o 5.6 Instrument transformers ∙ 6 Classification ∙ 7 Construction o 7.1 Cores ▪ 7.1.1 Laminated steel cores ▪ 7.1.2 Solid cores ▪ 7.1.3 Toroidal cores ▪ 7.1.4 Air cores 图形平移 o 7.2 Windings o 7.3 Coolant o 7.4 Insulation drying o 7.5 Terminals ∙ 8 Applications ∙ 9 See also ∙ 10 Notes ∙ 11 References ∙ 12 External links |
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[edit] History
[edit] Discovery
Faraday's experiment with induction between coils of wire [1]
The phenomenon of electromagnetic induction was discovered independently by Michael Faraday and Joph Henry in 1831. However, Faraday was the first to publish the results of his experiments and thus receive credit for the discovery.[2] The relationship between 和仲蒙夜坐
electromotive force (EMF) or "voltage" and magnetic flux was formalized in an equation now referred to as "Faraday's law of induction":
.
where is the magnitude of the EMF in volts and ΦB is the magnetic flux through the circuit (in webers).[3]
Faraday performed the first experiments on induction between coils of wire, including winding a pair of coils around an iron ring, thus creating the first toroidal clod-core transformer.[4]
[edit] Induction coils
Faraday's ring transformer
The first type of transformer to e wide u was the induction coil, invented by Rev. Nicholas Callan of 寻隐者不遇的作者Maynooth College, Ireland in 1836. He was one of the first rearchers to realize that the more turns the condary winding has in relation to the primary winding, the larger is the increa in EMF. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. Since batteries produce direct current (DC) rather than alternating current (AC), induction coils relied upon vibrating electrical contacts that regularly interrupted the current in the primary to create the flux changes necessary for induction. Between the 1830s and the 1870s, efforts to build better induction coils, mostly by trial and error, slowly revealed the basic principles of transformers.
