High frequency currents. Resonance transformer. Is the current safe? Lecture of Tesla on high frequency currents.

According to Tesla, the year he spent in Pittsburgh was lost to research in the field of multiphase currents. It is possible that this statement is close to the truth, but it is possible that this year was the beginning of the further creative success of the inventor. The discussion with the engineers at the Westinghouse plant did not pass without a trace. The justification of the frequency of alternating current proposed by him in 60 periods required a more thorough analysis of the economic efficiency of applying both lower and higher frequencies. Tesla's scientific conscientiousness did not allow him to leave this question without careful verification.

Returning in 1889 from Europe, he set about designing an alternator of high frequency and soon created a machine whose stator consisted of 348 magnetic poles. This generator made it possible to obtain an alternating current with a frequency of 10,000 cycles per second (10 kHz). Soon he managed to create an even more high-frequency generator and begin to study various phenomena at a frequency of 20 thousand periods per second.

Studies have shown that as the frequency of alternating current increases, the volume of iron in electromagnetic motors can be significantly reduced, and starting at a certain frequency, it is possible to create electromagnets consisting of windings alone, generally without iron in the coils. Engines made from such electromagnets without iron would be extremely light, but in many other respects uneconomical, and a reduction in metal costs would not pay off due to a significant increase in electricity consumption.

Examining a wide range of alternating current frequencies initially within the limits that could be applied in a multiphase system (25-200 periods per second), Tesla soon went on to study the properties and possibilities of the practical use of currents raised (10-20 thousand periods per second) and high (20-100 thousand periods per second) of frequencies. To obtain a much larger number of periods and much higher voltages than could be achieved by the generators of high frequency currents, it was necessary to find and rely on other principles. Well-known with the world literature on electrophysics and electrical engineering, Tesla studied the work of the famous American physicist Joseph Henry, who expressed in 1842 the assumption that with certain electrical discharges (including the discharge of the Leyden jar) there are not only "main categories" but also Counter, each succeeding somewhat weaker than the previous one. Thus, the existence of a damped two-sided electric discharge was observed for the first time.

Tesla also knew that eleven years after Henry the English physicist Lord Kelvin had experimentally proved that the electric discharge of a capacitor is a two-way process that continues until the energy is used up to overcome the resistance of the environment. The frequency of this two-way process reaches 100 million vibrations per second. The spark between the spark gap balls, seeming homogeneous, actually consists of several million sparks, passing in a short time in both directions.

Kelvin gave a mathematical expression of the process of double-sided discharge of the capacitor. Later, Fedderson, Schiller, Kirchhoff, Helmholtz and other researchers not only verified the correctness of this mathematical expression, but also significantly supplemented the theory of electric discharge. The sign was Tesla and with the work of Anton Oberbank, who observed the phenomenon of electrical resonance, that is, the process of a sharp increase in the amplitude (amplitude) of the oscillations as the external oscillation frequency approaches the frequency of the internal oscillations of the system.

It was well known to him and the experiments of Hertz and Lodge, engaged in the study of electromagnetic waves. Tesla was particularly impressed by the experiments of Heinrich Hertz, which confirmed the theoretical assumptions of James K. Maxwell on the wave nature of electromagnetic phenomena. It should be noted that in the works of Hertz Tesla for the first time found an indication of the phenomenon of so-called "standing electromagnetic waves," that is, waves superimposed one on top of the other so that they in one places strengthen each other, creating "antinodes", and in others reduce to Zero, creating "nodes."

Knowing all this, Nikola Tesla in 1891 completed the design of the device, which played an exceptional role in the further development of the most diverse branches of electrical engineering and especially radio engineering. To create currents of high frequency and high voltage, he decided to use the known property of resonance, that is, the phenomenon of a sharp increase in the amplitude of the natural oscillations of any system (mechanical or electrical) when external oscillations with the same frequency are applied to them. Based on this well-known phenomenon, Tesla created his resonant transformer.

The effect of a resonant transformer is based on tuning the resonance of its primary and secondary circuits. The primary circuit, containing both the capacitor and the induction coil, makes it possible to obtain alternating currents of very high voltage with frequencies of several million periods per second. The spark between the spark gap balls causes rapid changes of the magnetic field around the primary coil of the vibrator. These changes in the magnetic field cause the occurrence of a corresponding high voltage in the winding of the secondary coil consisting of a large number of turns of a thin wire, the frequency of the alternating current in it corresponding to the number of spark discharges reaches several million changes per second.

The frequency reaches its highest value at the moment when the periods of the primary and secondary circuits coincide, that is, when the phenomenon of resonance in these chains is observed.

Tesla developed very simple methods of automatically charging the capacitor from a low voltage power source and discharging it through an air core transformer. Theoretical calculations of the inventor showed that even with the smallest capacitance and induction values ​​in the resonant transformer created by him, with appropriate tuning, very high voltages and frequencies can be obtained by resonance.

The principles of electrical tuning of a resonant transformer discovered by him in 1890 and the possibility of changing the capacitance for changing the wavelength of electromagnetic oscillations created by a transformer have become one of the most important foundations of radio engineering, and Tesla's thoughts about the huge role of the capacitor and, in general, capacitance and self-induction in the development of electrical engineering were justified.

When creating a resonant transformer, one more practical task had to be solved: to find insulation for ultrahigh voltage coils. Tesla tackled the theory of insulation breakdown and based on this theory he found the best way to isolate coil turns - immerse them in paraffin, linseed or mineral oil, now called transformer. Later, Tesla once again returned to the development of electrical isolation issues and made very important conclusions from his theory.

Having barely begun experiments with high-frequency currents, Nikola Tesla clearly realized the great prospects that opened up before mankind with the wide use of high frequency currents. The direction of work of Tesla testifies to the unusually versatile conclusions he made from his discovery.

First of all, he came to the conviction that electromagnetic waves play an exceptionally important role in most natural phenomena. Interacting with each other, they either increase, or weaken, or cause new phenomena, the origin of which we sometimes attribute to completely different reasons. But not only electromagnetic radiation plays a huge role in the most diverse phenomena of nature. Tesla intuition of a great scientist understood the significance of various radiations before the remarkable discoveries of radioactive elements. When later, in 1896, Henri Becquerel, and then Pierre and Marie Curie discovered this phenomenon, Tesla found in this confirmation of his predictions, voiced by him back in 1890.

The enormous importance of alternating currents in the development of industry, which finally got the electric motor it needed, became clear to Nicole Tesla at the first acquaintance with the advantages of a three-phase current requiring only three wires for its transmission. For Tesla already at that time it was undoubtedly that a way of electricity transmission should be opened and completely without wires, with the help of electromagnetic waves. This problem attracted the attention of Tesla, became the subject of his studies as early as the end of 1889.

However, the practical application of high frequency currents for a variety of purposes required the study at first glance of a variety of unrelated issues. These and other experiments on a large scale began in Nikola Tesla's laboratory.

Having started systematic experiments with high-frequency and high-voltage currents, Tesla had to develop first of all measures to protect against the danger of electric shock. This particular, auxiliary, but very important task led him to discoveries that laid the foundation for electrotherapy - an extensive field of modern medicine.

The course of thought of Nikola Tesla was extremely original. It is well known, he reasoned, that a low-voltage direct current (up to 36 volts) does not have harmful effects on a person. As the voltage rises, the possibility of destruction increases rapidly.

With the increase in voltage, since the resistance of the human body is almost unchanged, the current strength also increases and reaches a threatening value at 120 volts. Higher voltage becomes dangerous for people's health and life.

The matter is different. For him, the limit of dangerous voltage is much higher than for a constant voltage, and this limit is pushed up with increasing frequency. It is known that electromagnetic waves of a very high frequency do not have any painful effect on a person ¹⁰ . An example of this is the light perceived at normal brightness by a healthy eye without any painful sensations. Within what frequencies and voltages is the alternating current dangerous? Where does the safe current start?

Step by step Tesla investigated the effect of an alternating electric current on a person at different frequencies and voltages. He spent experiments on himself. First, through the fingers of one hand, then through both hands, finally, through the entire body, he passed currents of high voltage and high frequency. Studies have shown that the effect of an electric current on the human body consists of two components: the effect of current on tissue and cells by heating and the direct action of current on nerve cells.

It turned out that heating does not always cause destructive and painful consequences, and the effect of current on nerve cells ceases at a frequency of over 700 periods, similar to how a person's hearing does not respond to fluctuations above 2,000 per second, and the eye to vibrations outside visible Colors of the spectrum.

Thus, the safety of high-frequency currents was established even at high voltages. Moreover, the thermal effects of these currents could be used in medicine, and this discovery of Nikola Tesla found wide application; Diathermy, treatment of UHF and other methods of electrotherapy is a direct consequence of his research. Tesla himself has developed a number of electrothermal devices and devices for medicine, which have become very popular both in the US and in Europe. His discovery was then developed by other outstanding electricians and physicians.

Once, while experimenting with high-frequency currents and bringing their voltage to 2 million volts, Tesla accidentally brought the copper disc painted with black paint to the equipment. At the same instant, a thick black cloud enveloped the disc and immediately rose, and the disc itself shone, as if someone's invisible hand scraped all the paint and polished it.

Surprised Tesla repeated the experience, and again the paint disappeared, and the disk shone, teasing the scientist. Repeating dozens of times with different metals, Tesla realized that he had discovered a way to clean them with high frequency currents.

"It is curious," he thought, "but whether these currents will affect the skin of a person, whether it will be possible to remove from them various, paints that are difficult to remove."

And this experience was a success. The skin of the hand, painted with paint, instantly became clean, as soon as Tesla brought it into the field of high frequency currents. It turned out that these currents can remove from the skin of the face a small rash, clean pores, kill microbes, always in abundance covering the surface of the human body. Tesla believed that his lamps have a special beneficial effect not only on the retina of the eye, but also on the entire nervous system of man. In addition, Tesla lamps cause ozonation of air, which can also be used in the treatment of many diseases. Continuing to engage in electrotherapy, Tesla in 1898 made a detailed report on his work in this area at the next congress of the American Electro-Therapeutic Association in Buffalo.

In the laboratory Tesla passed through his body currents of 1 million volts at a frequency of 100 thousand periods per second (current reached at the same magnitude of 0.8 amperes). But, operating with high-frequency and high-voltage currents, Tesla was very cautious and required his assistants to comply with all the rules of safety developed by him. So, when working with a voltage of 110-50 thousand volts at a frequency of 60-200 periods, he taught them to work with one hand to prevent the possibility of a current flowing through the heart. Many other rules, first established by Tesla, are firmly established in modern safety techniques when working with high voltage.

Having created a variety of apparatus for the production of experiments, Tesla in his laboratory began to study a huge range of issues related to a completely new field of science, in which he was most interested in the practical uses of high frequency and high voltage currents. His works encompassed a variety of phenomena, ranging from questions of generating (creating) currents of high frequency and ending with a detailed study of the various possibilities of their practical use. With each new discovery, more and more problems arose.

As one of the particular tasks, Tesla was interested in the possibility of using the discovery of the electromagnetic nature of light by Maxwell and Hertz. He had an idea: if light is electromagnetic waves with a certain wavelength, can it not be artificially obtained by heating the filament of an electric incandescent lamp (which makes it possible to use only 5 percent of the energy converted into a light flux), but by creating such oscillations, Which would cause the appearance of light waves? This task became the subject of research in the laboratory of Tesla in the beginning of 1890.

Soon he accumulated a huge number of facts that allowed us to proceed to generalizations. However, Tesla's caution forced him to check his assertions tens and hundreds of times. He repeated hundreds of times each experience before drawing any conclusions from him. The extraordinary nature of all the discoveries of Nikola Tesla and his enormous authority attracted the attention of the leaders of the American Institute of Electrical Engineers, again, like three years ago, invited Tesla to lecture about their work. Tesla chose the topic: "Experiments with alternating currents of very high frequency and their use for artificial lighting."

By tradition, established since the first years of the institute, a limited number of invitations were sent to only the most outstanding electrical engineers. Before such an elected audience on May 20, 1892, Tesla read one of his most inspired lectures and demonstrated the experiments already carried out by him in his laboratory.

- There is nothing that could more attract the attention of a person and would deserve to be studied than nature. To understand its enormous mechanism, to discover its creative forces and to know the laws that govern it, is the greatest goal of the human mind, "Tesla began his speech with these words.

And now he is already demonstrating to the listeners the results of his research in a new, yet unexplored region of high frequency currents.

"Scattering of electromagnetic energy in the space surrounding the source of high frequency currents makes it possible to use this energy for a variety of purposes," the scientist says with conviction and immediately shows a remarkable experience. He puts forward a brilliant position about the possibility of transmitting electricity without wires and in proof makes both ordinary incandescent lamps and specially created lamps without threads inside shine, introducing them into an alternating electromagnetic field of high frequency. "Lighting by lamps of this kind," says Tesla, "where light does not arise from the heating of threads by a flowing current, but because of the special vibrations of molecules and gas atoms, it will be easier than lighting with modern incandescent lamps. The lighting of the future, - the scientist emphasized, - is lighting by high-frequency currents.

Particularly detailed Tesla stopped describing his resonant transformer as a source of very high frequency waves and again stressed the value of the discharge of the capacitor in creating such oscillations. Tesla correctly estimated the great future of this most important detail of modern radio engineering means. He expressed this thought in the following words:

"I think that the discharge of a capacitor will play an important role in the future, since it will not only provide the opportunity to receive light in a simpler way, in the sense that the theory I have set forth, but will prove important in many other respects.

Having described in detail the results of experiments with high-frequency currents obtained with the help of a resonant transformer, Tesla concluded the lecture with words indicating his clear presentation of the significance of the further study of phenomena over which his work barely revealed the veil of secrecy:

- We pass with inconceivable speed through infinite space; Everything around us is in motion, and energy is everywhere. There must be a more direct way to utilize this energy than is currently known. And when the light comes from the environment around us and when all forms of energy from their inexhaustible source are obtained in the same way without effort, humanity will go forward in giant steps.

One contemplation of this magnificent perspective raises our spirit, strengthens our hope and fills our hearts with the greatest joy.

Under stormy applause Tesla finished his remarkable performance. The extraordinary nature of everything shown and the bold conclusions of the scientist, who saw the revolutionary consequences of his discoveries, astounded the listeners, although not all understood the contents of the lecture as deeply as Nichola Tesla wished.