electrical engineering(redirected from AC/DC (electrical))
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electrical engineering:see engineeringengineering,
profession devoted to designing, constructing, and operating the structures, machines, and other devices of industry and everyday life. Types of Engineering
The primary types of engineering are chemical, civil, electrical, industrial, and mechanical.
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the branch of science and technology associated with the use of electrical and magnetic phenomena to convert energy, obtain and alter the chemical composition of useful substances, produce and process materials, transmit information, and convert and use electric energy for practical human activities.
History. The advent of electrical engineering was preceded by a long period in which knowledge was accumulated about electricity and magnetism and during which only isolated attempts were made to use electricity in medicine and to transmit signals. In the 17th and 18th centuries works on research in electrical phenomena were written by M. V. Lomonosov, G. V. Rikhman, B. Franklin, C. A. de Coulomb, and P. Divisch. Of crucial importance to the establishment of electrical engineering was the construction of the first DC source—the voltaic pile (A. Volta, 1800). Subsequently, the creation of improved primary cells made it possible during the first third of the 19th century to carry out numerous investigations of the chemical, thermal, optical, and magnetic phenomena produced by electric currents (the works of V. V. Petrov, H. C. Oersted, D.-F. Arago, M. Faraday, J. Henry, A. M. Ampère, G. S. Ohm, and others). The foundations of electrodynamics were established during this period, and a major law of electric circuits—Ohm’s law—was discovered. The most notable attempts to apply the results of such advances were in the fields of telegraphy (the electromagnetic telegraph of P. L. Shilling 1832), military engineering (the electrochemical naval mines of B. S. Iakobi, 1840’s), and electrical measurement (the electric current indicator known as a multiplier, devised by the Austrian scientist J. S. C. Schweigger, 1820).
The discovery of electromagnetic induction (1831–32) paved the way for the appearance of electric machines—motors and generators. Inasmuch as all the first users of electric energy required direct current, which had been given the most study, the first electric machines were also DC designs. Electric motors were created before electric generators because during the first third of the 19th century primary cells more or less satisfied practical needs as a source of current. In the course of 50 years the design of the electric motor was improved from laboratory devices that demonstrated the possibility of converting electric energy into mechanical energy (Faraday’s installation, 1821) to industrial machines. In the first electric motors the moving element performed a reciprocating or oscillatory motion, and the torque on the motor’s shaft pulsated (as in Henry’s motor). Motors with a rotating armature were built beginning in the 1830’s. One such motor, used to propel an electric boat, was developed by Iakobi (1834–38).
Iakobi’s motor demonstrated the fundamental feasibility of practical applications as well as the need to create sources of electric energy that were more economical than primary cells. The electric generator, for which Faraday’s acyclic machine was the prototype (1831), filled this need. The first generators for practical use were magnetoelectric models, in which the magnetic field was produced by permanent magnets and the armatures were massive induction coils (Iakobi, 1842). In 1851 the German scientist W. J. Sinsteden proposed that the permanent magnets be replaced with electromagnets and that the windings be supplied from independent magnetoelectric generators. The subsequent development of generators centered on the use of the generator’s own current to excite the winding of the electromagnet. Such self-excited generators were proposed almost simultaneously by the Danish scientist S. Hjorth (1854), the British engineers C. F. Varley and S. A. Varley (1867), and A. I. Jedlik, C. Wheatstone, and W. von Siemens. The industrial production of generators was begun in 1870 in Paris, after Z. T. Gramme had become the first to use a laminated ring armature in a self-excited generator; the basic design of the armature had been proposed for an electric motor in 1860 by A. Pacinnotti. The Gramme machine operated both as a generator and as a motor, thus marking the first practical use of the principle of reversibility of electric machines (discovered by H. F. E. Lenz, 1832–38) and paving the way for wider application of electric machines.
The subsequent development of DC machines centered on improving their structural elements by replacing the ring armature with a drum armature (F. von Hefner-Alteneck, 1873), improving laminated armatures (the American inventor H. S. Maxim, 1880), and introducing a compensating-field winding (1884) and commutating poles (1885). By the 1880’s DC electric machines had acquired the principal structural features of modern machines. Their development was facilitated by the discovery of the law of the direction of induced currents (seeLENZ’S LAW), the detection and investigation of the counter electromotive force (Iakobi, 1840) and of armature reaction (Lenz, 1847), the development of computational methods for electric circuits (G. R. Kirchhoff, 1847) and for magnetic circuits (the British scientist J. Hopkinson, early 1880’s), and the study of the magnetic properties of iron (A. G. Stoletov, 1871). In the late 1870’s, J. C. Maxwell began his work on formulating the equations that are the foundation of the modern study of electromagnetic fields (seeMAXWELL’S EQUATIONS).
Chemical current sources were improved along with electric generators. The invention of the lead-acid storage battery by the French physicist G. Plante in 1859 was a major step in this direction. By the 1880’s an improved version of the battery already exhibited all the basic elements of modern batteries.
The development of reliable current sources made it possible to satisfy the growing demand for electric energy for practical use. The subsequent progress of electrical engineering is associated with the advent of the electrical engineering industry and the wide acceptance of electric lighting, which steadily replaced gas lighting from the 1850’s to the 1870’s. The idea of using electric energy for illumination was put forth by Petrov in 1802 in the wake of the discovery of the electric arc. The first electrical sources of light were variations of carbon arc lamps, of which the cheapest and simplest was called the Iablochkov candle (P. N. Iablochkov, 1876). Between 1870 and 1875, A. N. Lodygin developed several types of incandescent lamps, which were later improved by T. A. Edison and became the leading lamp type everywhere by the 1890’s. The achievements in the creation and application of electric light sources had an important influence on the establishment and development of illuminating engineering. The advent of electric power systems is linked with the spread of electric lighting. Iablochkov’s first lighting devices exhibited all the basic elements of energy systems: a prime mover, generator, power transmission line, transformer, and consumer.
The first use of electric energy for production purposes was the result of work carried out by Iakobi (1838), who proposed the use of electric current to make metallic copies of images and to deposit metallic coatings (seeELECTROPLATING TECHNOLOGY).
Expansion of the practical uses of electric energy was made possible only during the 1870’s and 1880’s, when the problem of transmitting electric energy over a distance was solved. In 1874, F. A. Pirotskii concluded that it would be economical to generate electric energy at sites where there were cheap fuels or hydroelectric resources and then to transmit the energy to the consumer. In 1880 and 1881, D. A. Lachinov and M. Deprez independently proposed to use high-voltage current in order to reduce power losses in transmission lines. The first DC power line, constructed by Deprez in 1882 between the cities of Miesbach and Munich, was 57 km long and carried a voltage of 1.5–2 kilovolts. However, attempts to transmit direct current proved inefficient because the technical facilities for obtaining high-voltage direct current were limited and direct current was inconvenient for the customer. As a result, as direct current was being used for power transmission, research was simultaneously being conducted on the use of single-phase alternating current for the same purposes; the alternating current could be changed in voltage (stepped up and stepped down) with a single-phase transformer. The development of an industrial single-phase transformer (O. Bláthy, M. Déri, and K. Zipernowski, 1885) essentially solved the problem of transmitting energy. However, the wide application of single-phase alternating current in industry was not as yet possible, because single-phase electric motors did not meet the requirements for an industrial electric drive. As a result, the use of single-phase alternating current was restricted to lighting installations.
In the 1870’s and 1880’s electric energy began to be used in production processes to obtain aluminum, copper, zinc, and high-quality steels; in the machining and welding of metals; and in the hardening of parts by means of heat treatment. In 1878, Siemens created an industrial electric furnace, and methods of arc welding were proposed by N. N. Benardos in 1885 and N. G. Slavianov in 1891.
The first attempts to use electric energy in transportation also date from the 1870’s, when Pirotskii tested a railroad car with an electric traction motor. In 1879, Siemens constructed an experimental electric railway in Berlin, and during the 1880’s trolley car lines were opened in many cities in Western Europe and later in the USA. In Russia the first trolley car went into service in Kiev in 1892. During the 1890’s electric traction was used on underground railways (in London in 1890 and in Budapest in 1896) and later on mainline surface railroads.
By the end of the 19th century, the industrial use of electric energy had changed into a major, integrated problem of technology and economics: in addition to the need for efficient power transmission, it was necessary to have an electric motor that met the requirements for an electric drive. The solution to the problem became possible after the development of polyphase, especially three-phase, AC systems (seeTHREE-PHASE CIRCUIT). Although many engineers and scientists worked on the problem (N. Tesla, the American C. S. Bradley, the German engineer F. A. Hasel-wander), an integrated solution was offered only in the late 1880’s by M. O. Dolivo-Dobrovol’skii, who created several industrial designs for three-phase asynchronous motors and three-phase transformers. In 1891, Dolivo-Dobrovol’skii, constructed a three-phase power transmission line between Laufen and Frankfurt am Mein—a distance of 170 km.
Modern electrical engineering. The practical application of three-phase systems marked the beginning of the modern development of electrical engineering, which is characterized by the growing electrification of industry, agriculture, transportation, and daily life. The increased demand for electric energy has been responsible for the construction of high-capacity power plants and distribution networks and for the creation of new electric power systems and the extension of existing systems. The construction of high-capacity, high-voltage transmission lines has led to the development of all types of high-voltage equipment and insulating materials as well as measurement methods and conversion technology. It has also given impetus to improvements in the design of electric machines and equipment and to the development of methods of analysis for the processes in AC circuits (notably, research by C. P. Steinmetz). The improvement of electrical engineering equipment has facilitated the organization of such scientific disciplines as high-voltage engineering, electric circuit theory, and the theory of electric machines and electric drives. Advances in electrical engineering have had a major influence on the development of radio engineering and electronics, remote control and automation, and computer technology and cybernetics.
One of the most important branches of electrical engineering is electromechanics, which deals with the problems of converting energy. The practical solution of problems of this nature on a broad scientific basis has necessitated the development of special methods for analyzing and describing the processes that take place in electrical engineering devices. The mathematical description of such processes is based on the solutions of Maxwell’s equations, which may be supplemented with equations describing the particular process; the variational principles of mechanics may also be used. Based on the virtual work principle, various formalized methods have been worked out for use in studying the processes that take place in electric systems, machines, and equipment. Those of the greatest practical importance include selection of the most convenient systems of generalized coordinates, analysis of transients in electric circuits, and determination of operating stability for regulated and unregulated electric machines that are connected to power transmission lines. Important contributions to the development of such methods have been made by A. A. Gorev, P. S. Zhdanov, S. A. Lebedev, and the British scientist O. Heaviside. Their works laid the foundation for the mathematical theory of electric machines and demonstrated the possibility of using complex mathematical procedures (tensor calculus, the theory of graphs, the theory of matrices, and operational calculus) to solve a variety of applied problems, especially those involving the study of complex electromechanical systems and electromechanical and electromagnetic transients. The use of the tensor calculus has resulted in the advent of research methods in which data characterizing an entire complicated system (such as an electric circuit containing hundreds and thousands of nodes and branches) can be obtained by analysis of the behavior of individual parts.
The application of formalized methods in combination with computer design techniques has proved particularly effective and is one of the most promising trends in the treatment of contemporary problems in electromechanics (especially synthesis problems, which may be solved by using the algebra of logic and the theory of directed graphs). Formalized methods are used in the study of many problems and tasks in electrical engineering, such as the investigation of nonlinear circuits and the harmonic and subharmonic oscillations that arise in them. Such research is conducted on the basis of methods for analysis and synthesis previously developed for linear circuits in the works of A. M. Liapunov, N. M. Krylov, N. N. Bogoliubov, L. I. Mandel’shtam, N. D. Papaleksi, and A. A. Andronov.
An important trend in modern electrical engineering is the development of theoretical and experimental research methods based on similarity theory, analogue and physical modeling, and the theory of experiment design; such methods make it possible to solve a number of fundamental scientific and technical problems in electrical engineering, including the improvement of existing means of power transmission and the development of new ones. Within the scope of such problems are the study of the processes that occur in power transmission lines and conversion equipment, the development and improvement of controlled elements in switching equipment, the creation of semiconductor converters capable of operating efficiently in combination with electromechanical devices (seeCONVERSION TECHNOLOGY), and investigation of the possibility of using superconductors for power transmission lines.
Of great practical importance is the development of optimum control methods for complex electric power systems and the improvement of the reliability of the systems. The solution of such problems requires the use of modeling methods and probability theory. A necessary condition for increasing the stability and operating reliability of electric power systems is the provision of highpower balancing devices, static regulators, and other equipment to ensure optimum operating conditions.
Two important trends in electrical engineering are the creation of complex electromagnetic fields with specific properties, which requires the development of methods for calculating and modeling electric and magnetic fields in ferromagnetic, plasma, and other nonlinear and anisotropic media together with the study and determination of optimum configurations for systems (particularly superconducting systems) that create strong magnetic fields; and the development of a theory of control for electromagnetic fields and methods of synthesizing systems that create such fields.
Of considerable interest is the investigation of high-intensity pulsed fields (seePULSE TECHNOLOGY, HIGH-VOLT AGE), including the development of methods for analyzing the interaction between such fields and matter and the study of thermal and electrodynamic processes in electric power devices having limit parameters. The results of such investigations are being used in the design of superpowered electric transformers and series reactors.
The theoretical and experimental methods of electrical engineering have been developed in various other branches of science and technology, particularly those associated with investigation of the properties of substances (semiconductors and plasmas), with the development and construction of equipment for nuclear and laser technology, with the study of phenomena of the microcosm and the vital activities of living organisms, and with the conquest of space.
The achievements of electrical engineering are being applied in all spheres of human activity—in industry, agriculture, medicine, and everyday life. The electrical engineering industry manufactures machines and equipment for the production, transmission, conversion, distribution, and consumption of electric energy. The range includes a variety of electrical engineering and production equipment; electrical measuring instruments and devices for telecommunication; regulating, monitoring, and control equipment for automatic control systems; electric household instruments and machines; and medical and scientific research equipment.
Scientific institutions, organizations, and periodicals. International organizations have played an important role in the progress of electrical engineering. Prominent examples include the International Electrotechnical Commission (IEC), the International Conference on Large High-Voltage Electric Systems (CIGRE), the International Power Industry Computer Application Conference, and Interelektro (International Electric). Soviet scientists take an active part in the work of these international organizations.
In the USSR scientific research in electrical engineering is conducted at the V. I. Lenin All-Union Electrical Engineering Institute (Moscow), the G. M. Krzhizhanovskii State Scientific Research Power Institute (Moscow), the All-Union Scientific Research Institute of Electromechanics (Moscow), the All-Union Scientific Research Institute of Electric Drive (Moscow), the All-Union Scientific Research Institute of Current Sources (Moscow), the Moscow Power Engineering Institute, the Leningrad Electrical Engineering Institute, the All-Union Scientific Research Institute of Electric Machine Building (Leningrad), the Scientific Research Institute of Direct Current (Leningrad), and many research centers in other cities in the Soviet Union.
Problems in electrical engineering are discussed in numerous periodicals. The USSR publishes the national journals Elektri-chestvo (Electricity), Elektrotekhnika (Electrical Engineering), and Elektricheskie Stantsii (Electric Power Stations). Abroad, the best-known journals are the EEl Bulletin (New York City, since 1933), Energy International (San Francisco, 1963), Revue de I’energie (Paris, 1949), and Electrical Review (London, 1872).
REFERENCESOsnovy elektrotekhniki. Edited by K. A. Krug. Moscow-Leningrad, 1952.
Istoriia energeticheskoi tekhniki SSSR, vols. 1–2, Moscow-Leningrad, 1957.
Istoriia energeticheskoi tekhniki, 2nd ed. Moscow-Leningrad, 1960.
White, D. C, and H. H. Woodson. Elektromekhanicheskoe preobrazovanie energii. Moscow-Leningrad, 1964. (Translated from English.)
Polivanov, K. M. Teoreticheskie osnovy elektrotekhniki, 2nd ed., parts 1 and 3. Moscow, 1972–75.
Zhukhovitskii, B. Ia., and I. B. Negnevitskii. Teoreticheskie osnovy elektrotekhniki, part 2. Moscow-Leningrad, 1965.
Seshu, S., and M. B. Reed. Lineinye grafy i elektricheskie tsepi. Moscow, 1971. (Translated from English.)
Mel’nikov, N. A. Matrichnyi metod analiza elektricheskikh tsepei, 2nd ed. Moscow, 1972.
Neiman, L. R., and K. S. Demirchian. Teoreticheskie osnovy elektrotekhniki, 2nd ed., vols. 1–2, Leningrad, 1975.
Steklov, V. Iu. V. I. Lenin i elektrifikatsiia, 2nd ed. Moscow, 1975.
Veselovskii, O. N., and Ia. A. Shneiberg. Energeticheskaia tekhnika i ee razvitie. Moscow, 1976.
Energetika SSSR v 1976–80gg. Edited by A. M. Nekrasov and M. G. Pervukhin. Moscow, 1977.
V. A. VENIKOV and IA. A. SHNEIBERG
electrical engineering[i′lek·trə·kəl ‚en·jə′nir·iŋ]
The branch of engineering that deals with electric and magnetic forces and their effects. See Engineering
Electrical engineers design computers and incorporate them into devices and systems. They design two-way communications systems such as telephones and fiber-optic systems, and one-way communications systems such as radio and television, including satellite systems. They design control systems, such as aircraft collision-avoidance systems, and a variety of systems used in medical electronics. Electrical engineers are involved with generation, control, and delivery of electric power to homes, offices, and industry. Electric power lights, heats, and cools working and living space and operates the many devices used in homes and offices. Electrical engineers analyze and interpret computer-aided tomography data (CAT scans), seismic data from earthquakes and well drilling, and data from space probes, voice synthesizers, and handwriting recognition. They design systems that educate and entertain, such as computers and computer networks, compact-disk players, and multimedia systems. See Character recognition, Computer, Control systems, Digital computer, Electric heating, Electric power generation, Electric power systems
The integration of communications equipment, control systems, computers, and other devices and processes into reliable, easily understood, and practical systems is a major challenge, which has given rise to the discipline of systems engineering. Electrical engineering must respond to numerous demands, including those for more efficient and effective lights and motors; better communications; faster and more reliable transfer of funds, orders, and inventory information in the business world; and the need of medical professionals for access to medical data and advice from all parts of the world. See Information systems engineering, Systems engineering