The physical essence of the phenomenon of transformation of currents has been reported in the chapter on the phone. It must, however, say a few words about the invention of this remarkable device, allowing you to solve the many large and small electrical problems. It is logical to say that the first transformer has appeared simultaneously with the discovery of the phenomenon of electromagnetic induction. One of the experiments was to Faraday that he blew current from the battery through the coil winding. Thus there is a current in the windings of the second coil, which is nearby, but it had nothing to do with the first. Instant current flow was detected galvanometer. Faraday himself, however, I never used this effect to convert the voltage.
In 1848 Ruhmkorff first drew the attention of physicists at the transformer amazing ability to create very high-voltage currents. But it took several more years before he was able to create a working model of this device. As a result, in 1852, came the famous Ruhmkorff induction coil, which played a huge role in the history of technology. In the manufacture of the first transformer to the inventor had to overcome considerable difficulties. In order to increase the number of turns in the winding of the secondary coil, Ruhmkorff had to use a very thin wire and at the same time carefully to make sure that the high voltage does not try to isolate it. Having bought a few kilometers as thin as hair, wire, he carefully insulate it, and then gently Naville on the coil turn to turn. Through its coil Ruhmkorff could receive current oscillations of very high voltage. DC can not be transformed. In order to convert DC battery into alternating current, Ruhmkorff series with the primary coil included chopper, which periodically make and break the current of the primary circuit (usually with a frequency of several tens to several hundred times per second). When the primary current circuit of the battery is induced in the secondary winding a voltage which was higher than the primary in the same ratio as was the number of turns in the secondary and primary windings. At the opening of the primary current is induced in the secondary even higher voltage. Its value was greater, the quicker it went tripping current. As the chopper was used spring plate that attracts the coil core and opens the circuit. interrupt frequency dependent on the mass and elasticity of the spring, on the number of turns in the primary winding and the battery voltage.
For several decades, almost no transformers used in engineering and scientific applications have exclusively. Only in the late 70-ies of the induction coils have been widely used in telephones and electric lighting device. The fact that after the spread in Europe spark Yablochkov electrical faced with a problem of so-called "crushing" of electrical energy. It consisted of the following. As a rule, one of the genset had to eat a lot of light bulbs. Meanwhile, a series connection of many candles network operation becomes unstable. The extinction of only one candle was tantamount to breaking the network, and then went out and the rest of the candles. If included in the spark circuit in parallel, it is usually lighted up only that one, which was the least resistance (because the current is known, there is always a line of least resistance). When the candle is completely burned off, sunbathing next to which was the least resistance, and so on. Faced with this problem, Yablochkov proposed to use for the "crushing" induction coil energy.
When this compound is included in series primary windings of the coils and the secondary winding, depending on the parameters may be included, one, two, three or more candles. Work coil while in the transformer mode, giving the required output voltage. With the extinction of the lamp chain is not interrupted, so that the individual candles continued to burn.
With the development of alternating current technology got transformers important. In 1882 Golyar and Gibbs took a patent for a transformer, which is used not only for the "fragmentation" of energy, but also to convert the voltage.
On a wooden support strengthened vertical number of induction coils, whose primary windings are connected in series. Secondary windings divided into sections, each section had a pair of pins for connecting the current receivers that operate independently of each other. The resistance in the primary circuit (and hence the current and power) can be controlled by moving the cores inside the coils. The cores of the primary and secondary windings are not connected to each other, so that these transformers have open magnetic system. Soon, however, it has been observed that if a secondary and primary coil spread on a single core, the transformer will work much better - reduced energy loss and increase efficiency. The first transformer with a closed magnetic system was created in 1884 by English inventor brothers Jones and Edward Hopkinson.
The core of the transformer has been assembled from steel strips or wires separated by an insulating material, which reduces the energy losses of eddy currents. This core is alternately placed high and low voltage coil.
In 1885, the Hungarian electrical engineer Deri proved that the transformers should be included in the chain in parallel, and took out a patent on the method of connection. Only after that has begun commercial production of transformers, single-phase AC. Since the power transformers were tested at their work significant overheating of the system of oil cooling (inside the transformer were placed ceramic vessel with oil) has been developed.
Transformers were extremely helpful and the three-phase system. In general, the three-phase current system would not have received in the first few years of the existence of such widespread use if it does not solve the problem of power transmission over long distances. But such a transfer, as will be shown below, is beneficial only if the high voltage, which in the case of alternating current, obtained by means of a transformer. Three-phase system did not represent fundamental difficulties for the energy transformation, but required three-phase transformers instead of one with a single-phase system. Such an increase in the number of relatively expensive equipment could not cause the desire to find a more satisfactory solution.
In 1889 Dolivo-Dobrovolsky invented the three-phase transformer core with a radial arrangement. In this case, the higher and lower voltages for each phase winding arranged on a respective radial cores consisted of a magnetic flux on the outer shell (outer yoke). Then Dolivo-Dobrovolsky has found that it is easier to place the rods in parallel with the windings and the ends of the rods (cores) to connect the same yoke. Then the whole system gets more compact. This type of transformer is called "prismatic".
Finally, in October 1891 Dolivo-Dobrovolsky took out a patent on a three-phase transformer with parallel rods arranged in a single plane. Its design was so successful that survives to this day almost unchanged.