12. Look at Fig. 11, name a, b, c, d, e and describe the figure.

LESSON EIGHTEEN

THE TRANSMISSION OF ELECTRIC POWER

One reason electricity serves us so well is that it can be generated in a suitable locality, transmitted over long distances, and supplied with almost unchangeable power to exactly the locality where it is wanted, i.e., where we want to use it and wherever wires can pass.

Until a hundred years ago, or so, power was never carried far away from its source. Later on, the range of transmission was expanded into a few miles. And now, in a comparatively short period of time, electrical engineering has achieved so much, that it is quite possible, at will, to convert mechanical power into electrical power and transmit it over hundreds of kilometres and more in any direction required. Then, electric power may be reconverted into mechanical power whenever and wherever it is desirable. It is not difficult to understand that the above process has been made possible owing to the generators, transformers, and motors, as well as to other necessary electrical equipment. We should also name here Dolivo-Dobrovolsky, the outstanding Russian electrical engineer, who was the founder of the three-phase technique. It was his invention that made possible the long-distance power transmission and, hence, electrification in the real sense of the word.

You will find below two examples illustrating the growth of electric power generation in our country: perhaps, you are familiar with the fact that the longest transmission line in prerevolutionary Russia was that connecting the Klasson Power Station with Moscow. It is said to have been built 70 km long, while the present Samara-Mos­cow high-tension transmission line is 900 kilometres long. ( the English terms "high-ten­sion" and "high-voltage" are interchange­able.)

Generally speaking, the length of high-tension transmission lines in our country is so great that they could cir­cle the globe six times.

It goes without saying that as soon as electric power is produced at the pow­er station, it is to be transmitted over wires to the consumer. However, the longer the wire, the greater is its resistance to current flow. On the other hand, the higher the offered resistance, the greater are the heating losses in electric wires. We can lower these undesirable losses in two ways, namely, we can reduce either the resistance, or the current. It is easy for us to see how one can reduce re­sistance: it is necessary to make use of better conducting material and as thick wires as possible. However, such wires would require too much material and, hence, they would be too expensive. Can the current be reduced? It is quite possible to supply the consumer with the amount of power he needs and at the same time to reduce the current in the transmission line by employing transformers. In effect, the unnecessary waste of useful power has been greatly decreased due to high-voltage lines, so that one may transmit power over long distances with small loss. High voltage means low current, low current, in its turn, results in reduced heating losses in electrical wires. It is dangerous, however, to use power at very high voltages for anything but transmission and distribution. For that reason, the voltage is always lowered again before the power is made use of.

Russian scientists are successfully developing quan­tum generators, called lasers, for emitting light amplitude radio waves. Theoretical calculations have shown that lasers are very likely to transform the power of light radio waves into electrical power with an efficiency amounting to about 100 per cent. It means that electrical power might be trans­mitted over considerable distances with negligible losses and what is very important without the use of transmission lines.