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For other uses, see Transformer (disambiguation).
Three-phase pole-mounted step-down transformer.
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic field. This changing magnetic field induces a changing voltage in the second circuit (the secondary). This effect is called mutual induction.
If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit.
The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings:
By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.
Transformers are some of the most efficient electrical 'machines', with some large units able to transfer 99.75% of their input power to their output. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide.
1. The transformer in this applet is assumed (1) no flux leakage and (2) no resistance in the two windings .
2. The inductances of the two windings are NOT assumed to be infinite. However, you may assign large inductances to them by selecting "Larger inductance".
4. Click the switch to open or close it.
5. Change the parameters by dragging the ends of corresponding bars.
6. Please note that it is pointless to compare the amplitude of a voltage and that of a current when they are dispalyed simultaneously on the screen. They have different units