ELETTROTECNICA. — After the discovery of electromagnetic, electrothermal, and electrochemical phenomena, no one could doubt the possibility of significant practical applications of electric currents; but certainly no one would have dared to imagine that, within a century, they would assume their present proportions.
Given the impossibility of entering into detail, we shall merely indicate in summary what the salient features of the present-day technology of electricity are.
I. INDUSTRIAL PRODUCTION OF ELECTRIC CURRENTS
However surprising and useful for the development of electrology, the production of electric currents by means of batteries, even the most perfected, proved too limited, inconvenient, and costly to be employed on a broad scale. Consequently, immediately after the discovery of the phenomena of electromagnetic induction, which made it possible to produce electric currents by another means, the problem of their realization on an industrial scale became pressing. The first apparatuses, still of extremely limited power, consisting of circuits by means of which lines of force emanating from permanent magnets were made to link alternately, demonstrated the possibility of solving the problem, but at the same time revealed its difficulty. The currents that could be produced in this way, besides still being too weak, were alternating and could practically be used only to deliver the so-called electric shocks, sometimes for therapeutic purposes, but more often as an amusing novelty.Only in 1860 did A. Pacinotti succeed in constructing the first machine which, after further improvement, could automatically supply a direct current. Theoretically, the problem could be regarded as solved, but only about a decade later was the first industrial mechanical generator of electric current (electric dynamo) constructed in France, operating according to Pacinotti’s principle.
Today, generators of direct currents with powers of thousands of HP and also very high voltages (thousands of volts) are constructed according to various principles throughout the world.
But in this field of human activity as well, a costly revolution took place. Alternating currents (which periodically reverse their direction), which could have been produced in considerable quantities long before direct currents and which were thought to be of little or no practical use, are now instead by far the most widespread, whereas direct currents con-
It is interesting to understand the reasons for this development, because it concerns economic and social interests of great importance.
The first installations for the production of electrical energy were, for the most part, as we say today, electrothermal; that is, they used thermal energy as the primary energy to be transformed. It is readily understandable that in many countries, especially those poor in natural fuels, there arose a desire to make use of hydraulic energy as the primary energy source. But water resources are found in conditions more favorable for utilization in the mountains and, in general, far from the major centers where the electrical energy obtained can be used advantageously. Thus the problem arose of transporting that energy over great distances.
Now, according to the fundamental laws of electric currents, it is known that power losses on a transmission line are reduced the more the current intensity is lowered and, consequently, the voltage increased. But extremely high voltages (above a few thousand volts) cannot be obtained directly with machines producing either direct or alternating currents; for the latter, however, there is the possibility of transforming them further to extremely high voltages (even several hundred thousand volts) by means of the so-called static transformers, extremely simple devices based on the phenomena of mutual induction, in which no mechanism is involved. By means of other analogous transformers at the point of arrival, operating in the opposite direction, the current can be transformed back to the distribution voltage. Thus the problem of transmission for alternating currents was solved in a more than satisfactory manner.
The other difficulties involved in the use of alternating currents were also overcome. For their use in lighting, it sufficed that their frequencies (their alternations per second) be no lower than 90; for their use in supplying motors, which in turn drive every kind of machine, there was required, in the great majority of cases, another major Italian invention: the rotating magnetic-field motor, devised and developed by Galileo Ferraris. It is because of this combination of circumstances that alternating currents prevailed and spread everywhere.
Where direct current is necessary (e.g., for electrolytic purposes), or where it is almost universally preferred (e.g., for railway and tramway traction), the so-called converters are used: complex machines which, when supplied with alternating currents, produce direct currents at the voltages required for use.
At this point it is interesting to observe that the processes mentioned above are advantageous only because the efficiency (that is, the ratio between what is expended and what is obtained) of electromagnetic transformations is extremely high in comparison with that of other transformations in other fields of physics. Whereas, for example, the efficiency of machines that transform thermal energy into mechanical energy (heat engines) ranges between ten and thirty percent, that of analogous machines transforming electrical energy into mechanical energy or vice versa may exceed ninety percent, and that of devices transforming electrical energy from one form into another is even higher. Static transformers, moreover, can attain efficiencies of as much as ninety-nine percent.
II. ELECTROLYTIC UTILIZATIONS OF CURRENTS
These applications, which began on the modest scale of silver-plating or gilding, or of the electroplating of a few medals, have now assumed enormous proportions. All the copper used in the increasingly widespread electrical machinery and installations is refined, that is, reproduced electrolytically. All the aluminum, a large part of the soda and hypochlorites produced in the world, and innumerable other chemical products are prepared through electrolytic processes. It is therefore no exaggeration to say that a considerable part of the electrical energy produced is absorbed by the electrochemical industries.BIBLI: E. Gerard, Leçons sur l'électricité, Parigi, various editions; L. Lombardi, Lexical di e., 2 vols., Torino, various editions; E. Kistler, Handbuch der Elektrotechnik, 2 vols., Stoccarda, various editions.