33 The simplest type of transformer is the singlephase one, which has only one set of windings. Other kinds of transformers, threephase ones, have three sets of windings and are mainly used in industry. Search the Internet and find out which of the devices that we use every day need a transformer. TRANSFORMERS What is a transformer? A transformer is a device that transfers electrical energy from one alternating-current circuit to one or more other circuits, either increasing (stepping-up) or reducing (stepping-down) the voltage. Basic transformers are made up of a magnetic core, usually an iron square, with two coils of wire wound around it. The primary winding is connected to the source of the input voltage, which is the voltage that has to be changed, while the secondary winding provides the resulting output voltage. How do transformers work? Transformers work on the principle of electromagnetic induction. When alternating current flows through the primary winding, it produces a magnetic field surrounding the winding, which induces an alternating voltage in the secondary winding. The ratio between the input and the output voltage is proportional to the number of turns of wire in each winding. Therefore, if the primary winding has more turns than the secondary one, the voltage will be stepped down; if the secondary winding has more turns of wire than the primary one, the voltage will be stepped up. Main applications of transformers Transformers are used for a wide variety of applications: big transformers are used in electrical power stations to transmit power at high voltages or to lower the voltage in transmission lines before electricity reaches the final users; signal and audio transformers are much smaller and are used to match the output of microphones and other audio devices to the input of amplifiers; transformers are used in batteries and charging sources to regulate the voltage. TRANSFORMER IP Primary circuit core: nucleo ratio: rapporto winding: avvolgimento 84 ELECTRICITY IS VP VS NP Turns NS Transformer Turns Secondary circuit