Carpool lanes, like this one on a California freeway near the Westwood neighborhood in Los Angeles, were designed to encourage more people per car. (Corbis-Bettmann) Transformers
A transformer is an electrical component used to connect one alternating current (ac) circuit to another through the process of electromagnetic induction. The input current travels through a conductor (the primary) wound around a conductive core. The current traveling through the primary windings creates an alternating magnetic field in the core. An output conductor (the secondary) is wound around the same core so that the magnetic field cuts through the secondary windings, inducing the output electrical current. For most transformers, the primary and secondary windings never come into direct electrical contact with each other. Instead, the transfer of energy from primary to secondary is accomplished solely through electromagnetic induction.
Transformers were developed through a series of scientific discoveries in the nineteenth century. Most notably, Michael Faraday showed in 1831 that a variable magnetic field could be used to create a current, thus pioneering the concept of electromagnetic induction. It was not until the 1880s that Nikola Tesla was able to use this principle to bolster his patents for a universal ac distribution network.
The majority of power transformers change the voltage from one side of the transformer to the other. The change in voltage is directly related to the number of turns each conductor (primary and secondary) makes around the transformer's core. For example, if the primary makes ten turns around the core, and the secondary makes five turns around the core, the secondary voltage will be half of the primary voltage. This type of transformer would be called a step-down transformer, since it steps down the voltage. On the contrary, if the number of turns in the primary is less than the number of turns in the secondary, the transformer will be a step-up transformer.
The power transformer also must maintain a balance of power from one side to the other. Power is the product of voltage and current. Therefore, neglecting any internal losses, if a transformer steps up the voltage by a given factor, it will also step down the current by the same factor. This has great application in the generation and transmission of electricity. It is difficult to generate extremely high voltages of electricity. Generating plants produce electricity at a relatively low voltage and high current, and step the voltage up to transmission levels through a transformer. This has the added effect of reducing transmission losses, since as the voltage increases, the current decreases, thereby reducing resistive voltage drops.
Iron (or steel) is frequently used as a transformer core because it provides adequate magnetic flux at a relatively low reluctance. In other words, iron cores, however, require additional design considerations to prevent excessive power losses and heat dissipation. The changing magnetic field inside the core creates current not only in the secondary windings of the transformer but also within the core itself. Using a laminated core constructed from small laminated plates stacked together and insulated from each other reduces these losses.
Other types of transformers include instrument, radio-frequency, wide-band, narrow-band, and electronic transformers. Each of these transformers operates similarly and is used in specific applications best suited for the transformer's design characteristics.
Electric Motor Systems; Electric Power, Generation Of; Electric Power Transmission and Distribution Systems; Faraday, Michael; Magnetism and Magnets; Tesla, Nikola.
Bibliography
Faraday, M. (1965). Experimental Researches in Electricity. New York: Dover Publications.
Fink, D. G., and Beaty, H. W., eds. (1993). Standard Handbook for Electrical Engineers, 13th ed. New York: McGraw-Hill.
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