ELECTROTECHNICS. - After the discovery of electromagnetic, electrothermal and electrochemical phenomena, no one could doubt the possibility of notable practical applications of electric currents, but certainly no one would have dared to think that within a century they would take on their present proportions.
Given the impossibility of going into details, only a summary mention will be made of the salient characteristics of the present-day technology of electricity.
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 ones, proved too limited, inconvenient and costly to be widely employed. Therefore, immediately after the discovery of the phenomena of electromagnetic induction, which made it possible to produce electric currents by another route, the problem of achieving this on an industrial scale became pressing. The first apparatuses, still of very limited power, consisting of circuits with which lines of force emanating from permanent magnets were made to concatenate alternately, demonstrated the possibility of a solution to the problem, but at the same time revealed its difficulty. The currents that could thus be produced, besides being still too feeble, turned out to be alternating and could practically be used only to give so-called electric shocks, sometimes for therapeutic purposes, but more often as an amusing novelty.
Only in 1860 did A. Pacinotti succeed in building the first machine which, further perfected, could automatically supply a direct current. Theoretically the problem could be considered solved, but only after about a decade was the first industrial mechanical generator of electric current (electric dynamo) built, constructed in France but operating on Pacinotti's principle.
Now generators of direct currents of powers of thousands of HP and of even very high voltages (thousands of volts) are built according to various criteria throughout the world.
But even in this sector of human activity a costly revolution took place. Alternating currents (which reverse their direction periodically), which could have been produced in considerable proportions well before direct currents, and which were believed to be scarcely and not at all usable in practice, are now instead by far the most widespread, while direct currents are employed almost only for particular purposes, especially for traction (railways and tramways) and electrochemical ones.
It is interesting to understand the reasons for this evolution because it touches economic and social interests of great importance.
The first plants for the production of electrical energy were largely, as one says today, electrothermal, that is, they used thermal energy as the primary energy to be transformed. It is immediately understandable that in many countries, especially those poor in natural fuels, the desire arose to use water power as primary energy. But these are found in better conditions for utilization among the mountains and in general far from the great centers where the electrical energy obtained can be advantageously used. Thus arose the problem of transporting that energy even over great distances.
Now, according to the fundamental laws of electric currents, it is known that the power losses on a transmission line are smaller the lower the current intensity and consequently the higher the voltage. But very high voltages (greater than a few thousand volts) cannot be obtained directly with the machines producing either direct or alternating currents; for the latter, however, there exists the possibility of further transforming them to very high voltages (even of several hundred thousand volts) by employing so-called static transformers, very simple devices based on the phenomena of mutual induction, in which no mechanism is involved. By means of other similar transformers at the arrival point operating in the reverse sense, the current can be retransformed to the distribution voltage. Thus the problem of transmission for alternating currents was solved in a more than satisfactory manner.
The other difficulties inherent in the utilization of alternating currents were also overcome. For their use for lighting purposes it was enough that their frequencies (their alternations per second) be not lower than 90; for their use in supplying motors, which in turn drive every sort of machine, another great Italian invention was needed in the great majority of cases: the rotating magnetic field motor, conceived and built by Galileo Ferraris. And it is because of this complex of things that alternating currents imposed themselves and spread everywhere.
Where direct current is needed (e.g., for electrolytic purposes) or where it is only almost generally preferred (e.g., for railway and tramway traction), so-called converters are employed, complex machines which, fed by alternating currents, produce direct currents at the utilization voltages.
At this point it is interesting to observe that the aforementioned processes prove convenient only because the efficiency (that is, the ratio between what is spent and what is obtained) of electromagnetic transformations is very high compared with other transformations in other fields of physics. While, for example, the efficiencies of machines that transform thermal energy into mechanical energy (thermal motors) hover between ten and thirty percent, that of the analogous machines that transform electrical energy into mechanical energy or vice versa can be higher than ninety percent, and even higher that of the devices that transform electrical energy from one form to another. Static transformers, moreover, can reach efficiencies of ninety-nine percent.
II. ELECTROLYTIC USES OF CURRENTS
These applications, which began on the modest scale of silvering or gilding or the electroplating of some medal, have now assumed enormous proportions. All the copper used in the ever more widespread electrical machinery and installations is refined, that is, reproduced electrolytically. All the aluminum, a good part of the soda and of the hypochlorites produced in the world, and countless 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.