How to increase the voltage frequency. How to increase the current without changing the voltage? What is current strength

10.02.2022

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The most popular method of increasing (or decreasing) the current frequency today is the use of a frequency converter. Frequency converters make it possible to obtain from a single-phase or three-phase alternating current of industrial frequency (50 or 60 Hz) the current of the required frequency, for example from 1 to 800 Hz, to power single-phase or three-phase motors.

Along with electronic frequency converters, in order to increase the frequency of the current, electroinduction frequency converters are also used, in which, for example, an asynchronous motor with a phase rotor operates partially in generator mode. There are also umformers - motor-generators, which will also be discussed in this article.

Electronic frequency converters

Electronic frequency converters allow you to smoothly adjust the speed of synchronous and asynchronous motors due to a smooth increase in the frequency at the output of the converter to a predetermined value. The simplest approach is provided by setting a constant V / f characteristic, and more advanced solutions use vector control.

Usually, they include a rectifier that converts industrial frequency alternating current into direct current; after the rectifier there is an inverter, in its simplest form - based on PWM, which converts the direct voltage into an alternating load current, and the frequency and amplitude are already set by the user, and these parameters may differ from the network parameters at the input up or down.

The output unit of an electronic frequency converter is most often a thyristor or transistor bridge, consisting of four or six switches, which form the required current to power the load, in particular, the electric motor. To smooth out noise in the output voltage, an EMC filter is added at the output.

As mentioned above, an electronic frequency converter uses thyristors or transistors as keys for its work. To control the keys, a microprocessor module is used, which serves as a controller and simultaneously performs a number of diagnostic and protective functions.

Meanwhile, frequency converters are still of two classes: with direct connection, and with an intermediate DC link. When choosing between these two classes, the advantages and disadvantages of both are weighed, and the expediency of one or the other for solving an urgent problem is determined.

with direct connection

Direct-coupled converters are distinguished by the fact that they use a controlled rectifier, in which groups of thyristors, alternately unlocking, switch the load, such as motor windings, directly to the mains.

As a result, pieces of sinusoids are obtained at the output. mains voltage, and the equivalent output frequency (for the motor) becomes less than the mains frequency, within 60% of it, that is, from 0 to 36 Hz for a 60 Hz input.

Such characteristics do not allow to vary the parameters of equipment in the industry over a wide range, and therefore the demand for these solutions is low. In addition, non-lockable thyristors are difficult to control, the cost of circuits becomes higher, and there are many noises at the output, compensators are required, and as a result, the dimensions are high and the efficiency is low.

With DC link

Much better in this regard are frequency converters with a pronounced DC link, where first the alternating mains current is rectified, filtered, and then again converted into an alternating current of the desired frequency and amplitude by an electronic switch circuit. Here the frequency can be much higher. Of course, double conversion somewhat reduces the efficiency, but the output parameters in terms of frequency just meet the requirements of the consumer.

In order to get a pure sine on the motor windings, an inverter circuit is used, in which the voltage of the desired shape is obtained thanks to. The electronic keys here are lockable thyristors or IGBT transistors.

Thyristors withstand large pulse currents compared to transistors, therefore, more and more often they resort to thyristor circuits, both in converters with direct connection and in converters with an intermediate DC link, the efficiency is up to 98%.

In fairness, we note that electronic frequency converters for the supply network are a non-linear load, and generate higher harmonics in it, this worsens the quality of electricity.

In order to convert electricity from one of its forms to another, in particular, to increase the frequency of the current without the need to resort to electronic solutions, so-called umformers are used - motor-generators. Such machines function like a conductor of electricity, but in fact there is no direct conversion of electricity, such as in a transformer or in an electronic frequency converter, as such.

The following options are available here:

direct current can be converted into alternating current of higher voltage and required frequency;

direct current can be obtained from alternating;

direct mechanical frequency conversion with increase or decrease thereof;

obtaining a three-phase current of the required frequency from a single-phase mains frequency current.

In the canonical form, the motor-generator is an electric motor, the shaft of which is directly connected to the generator. At the output of the generator, a stabilizing device is installed to improve the frequency and amplitude parameters of the received electricity.

In some models of umformers, the armature contains both motor and generator windings, which, and the conclusions of which are connected, respectively, to the collector and to the output slip rings.

In other cases, there are common windings for both currents, for example, there is no collector with slip rings to convert the number of phases, but taps are simply made from the stator winding for each of the output phases. So an asynchronous machine converts a single-phase current into a three-phase one (identical in principle to an increase in frequency).

So, the motor-generator allows you to convert the type of current, voltage, frequency, number of phases. Until the 70s, converters of this type were used in the military equipment of the USSR, where they fed, in particular, lamp devices. Single-phase and three-phase converters were fed with a constant voltage of 27 volts, and the output was an alternating voltage of 127 volts 50 hertz single-phase or 36 volts 400 hertz three-phase.

The power of such umformers reached 4.5 kVA. Similar machines were also used in electric locomotives, where a direct voltage of 50 volts was converted to an alternating voltage of 220 volts with a frequency of up to 425 hertz to power fluorescent lamps, and 127 volts 50 hertz to power passengers' razors. The first computers often used umformers for their power supply.

To this day, you can still find umformers in some places: on trolleybuses, in trams, in electric trains, where they were installed in order to obtain low voltage to power control circuits. But now they have already been replaced almost completely by semiconductor solutions (on thyristors and transistors).

Converters of the motor-generator type are valuable for a number of advantages. Firstly, it is a reliable galvanic isolation of the output and input power circuits. Secondly, the output is a pure sine without interference, without noise. The device is very simple in its design, and maintenance is quite simple.

This is an easy way to get three-phase voltage. The inertia of the rotor smooths out current surges when the load parameters change sharply. And of course, it is very easy to recuperate electricity here.

It was not without its shortcomings. Umformers have moving parts, hence their resource is limited. Mass, weight, abundance of materials, and as a result - high cost. Noisy operation, vibrations. The need for frequent lubrication of bearings, cleaning of collectors, replacement of brushes. Efficiency within 70%.

Despite the shortcomings, mechanical motor generators are still used in the electric power industry to convert large powers. In the future, motor generators may well help to coordinate networks with frequencies of 60 and 50 Hz, or to provide networks with increased requirements for power quality. Power supply of the rotor windings of the machine in this case is possible from a low-power solid-state frequency converter.

Instruction

Connect the electric motor to a variable EMF current source. Increase its value. Together with it, the voltage on the motor windings will increase. Keep in mind that if we neglect the losses on the supply conductors, which are very small, then the EMF of the source is equal to the voltage on the windings. Calculate the increase in motor power. To do this, find, at times, the voltage, and square this value.

Example. The voltage on the motor windings was increased from 110 to 220 V. How many times is its power? The voltage has increased by 220/110=2 times. Therefore, the engine power has increased by 2²=4 times.

Rewind the motor winding. In the vast majority of cases, a copper conductor is used for the motor winding. Use a wire of the same length, but with a larger cross section. The resistance of the winding will decrease, and the current in it of the motor will increase by the same amount. The voltage on the windings must remain unchanged.

Example. A motor with a winding cross section of 0.5 mm² was rewound with a wire with a cross section of 0.75 mm². How many times has its power increased, if unchanged? The cross section of the winding increased by 0.75/0.5=1.5 times. The engine power has also increased by the same amount.

When connecting a three-phase asynchronous motor to a household single-phase network, increase its useful power. To do this, turn off one of its windings. The braking torque generated during the operation of all windings will disappear, and the useful power of the motor will increase.

Increase the power of an AC induction motor by increasing the frequency of the AC current flowing through the windings. To do this, connect a frequency converter to the motor. By increasing the frequency of the supplied current on it, increase the power of the electric motor. Fix the power value with a tester operating in the wattmeter mode.

You will need

- capacitor;
- generator;
- key;
- wires.

Instruction

Assemble a circuit with a capacitor in which a sinusoidal voltage creates an alternator current.

At zero voltage at the moment of closing the key in the first quarter of the period, the voltage at the generator terminals will begin to increase, and the capacitor will begin to charge. A current will appear in the assembled circuit, but, despite the fact that the voltage on the generator plates is still quite small, the value current in the circuit will be the largest (the value of its charge).

Note that as the discharge of the capacitor decreases, the indicator current in the circuit decreases, and at the moment of complete discharge, the current is zero. In this case, the voltage value on the capacitor plates will constantly increase, and at the moment of complete discharge of the capacitor it will reach its maximum value (i.e. the value will be completely opposite to the voltage on the generator plates). Thus, we can conclude: at the initial moment of time, the current with the greatest force will rush into the uncharged capacitor, and as it is charged, it will begin to decrease completely.

note

Remember that as the frequency of the current increases, the resistance of the capacitor to AC (capacitor capacitance) also decreases. Thus, the capacitance of the resistance is inversely proportional to the capacitance of the circuit and the frequency of the current supplying it.

Useful advice

A capacitor is a fairly versatile element. When it's discharged, it behaves like short circuit- the current flows through it without restrictions, and its value tends to infinity. When it is charged, an open circuit occurs at this point in the circuit and the voltage of the circuit begins to constantly increase. It turns out an interesting relationship - there is voltage, but no current, and vice versa. Therefore, it is possible to achieve an increase in the frequency of the current only with a discharged capacitor, which comes into this state with a certain interval the required number of times. Use this information when creating a circuit.

3.2.1 An increase in the frequency of the current occurs when there is an excess of generated power due to the disconnection of powerful consumers, power interconnection nodes, breaking interconnections, and allocating a power plant to power a separate power interconnection node.

3.2.2 With an increase in frequency, an asynchronous run may occur, as a result of which the destruction of the turbine and generator rotors, damage to the auxiliary equipment of the power plant can occur. The duration of operation of turbogenerators at increased frequency is limited. In the event of a sudden (within a few seconds) increase in frequency up to 50.1 Hz, together with the dispatcher, the reason for the increase in frequency is determined, and if the frequency is more than 50.2 Hz, the NSS, with the permission of the power association dispatcher, takes the necessary measures to change the generating capacity of the thermal power plant in order to reduce frequencies in the power system. At the same time, the flows along the lines extending from the power plant are controlled.

3.2.3 When the frequency rises above 50.4 Hz, when the control capabilities of TPPs and HPPs in terms of lowering the frequency are practically exhausted (the emergency unloading of the NPP begins), the operating personnel of the power plant take measures to lower the frequency by shutting down or unloading the required number of power units as agreed with the dispatcher . In this case, the blocks are turned off while saving the s.s. or blocks remain in the network with the lowest possible load. The reduction in the generated power is carried out by remote influence (in addition to the action of automatic regulators) on the turbine power control system and on the reduction of the steam output of the boilers, while maintaining acceptable parameters and a stable operating mode of the boilers and controlling the flows along the lines extending from the power plant.

3.2.4 Heads of shifts of power plants allocated for independent actions of personnel, with a further increase in frequency to 51.5 Hz (unless otherwise indicated in the instructions of the enterprise) without instructions from the power pool dispatcher (operational personnel of the control room only at the direction of the NSS), urgently reduce the generated power by turning off part of the units or power units , while maintaining acceptable parameters and a stable mode of operation of the boilers.

The list of equipment that can be switched off independently by the personnel, as well as the order of switching off, are given in the instructions of the organization. This takes into account the conditions for maintaining nutrition s.s. power plants, maintaining off-line boilers and turbines at idle for subsequent synchronization of generators and power generation.

3.2.5 The personnel of the power plant should immediately notify the dispatcher of the power pool about emergency shutdowns of equipment performed independently.

3.2.6 In special cases, when, when increasing the frequency in individual power systems (nodes of power systems), it turns out to be necessary to prevent the automatic unloading of the station (ARS) from operating in order to maintain stability for any specific intersystem or intrasystem communications, the operating personnel of the power plant, within the limits of reserves and permissible overloads, increases the power turbines and steam capacity of boilers or, in extreme cases, retains their previous load. In this case, if necessary, those automatic devices are deactivated, the operation of which interferes with the implementation of the requirements of the regime.

The grounds for these actions of operational personnel can be:

Obtaining orders from higher operational personnel;

Operation of a special command alarm;

Reliable detection (by instruments and signals) of the occurrence of a regime requiring just such actions (if it is provided for by the enterprise's instructions).

3.2.7 In case of a sharp increase in frequency (51 Hz or more) with the occurrence of oscillations when the ARS fails, the TPP personnel are allowed to disconnect the turbogenerators from the network with the possibility of re-synchronization. In this case, the turbogenerators must operate at s.n. while maintaining the nominal speed. Personnel must carefully monitor the parameters of boilers and turbogenerators, preventing violations of the regime and ensuring their readiness for inclusion in the network, as well as for loading.

Asynchronous Modes

3.3.1 An asynchronous mode in a power grid may occur as a result of a violation of static or dynamic stability due to an overload of intersystem transit links (emergency shutdown of large generating capacity, a sharp increase in power consumption, failure of emergency automatic devices), failure of switches or protections during short circuit, non-synchronous switching on of links (for example, non-synchronous automatic reclosure ). In this case, the synchronism of individual power plants in relation to the power pool or between the individual parts of the power pool is disrupted and an asynchronous run occurs.

In addition to the asynchronous modes listed above, sometimes for other reasons, an asynchronous operation of a separate generator operating with excitation occurs in the power pool, and an asynchronous operation of the generator occurs when it loses excitation.

3.3.2 A sign of the asynchronous operation of individual power plants in relation to the power pool or between separate parts of the power pool is stable deep periodic current and power fluctuations at power plants and over the communication line, determined by the swing of the ammeter and wattmeter needles in the circuits of generators, transformers, power lines. Characteristic is the occurrence of a frequency difference between the parts of the power systems that have gone out of synchronism, despite the preservation of the electrical connection between them. Simultaneously with fluctuations in current and power, voltage fluctuations are observed. The largest voltage fluctuations usually occur at points close to the center of the swing. The most probable point of the swing center is the middle of the transit transmission lines connecting the out-of-sync power plants or parts of the power system. As you move away from the center of the oscillations, the voltage fluctuations decrease to inconspicuous values. However, depending on the configuration of the system and the ratio of inductive reactances, the swing center may also be on the busbars of the power plant. On the buses of power plants located near the center of oscillations, periodic deep voltage fluctuations occur with a decrease in it below the emergency allowable values, including s.n. with the possible shutdown of responsible mechanisms s.n. and individual units. The generators of these power plants are characterized by a violation of synchronism with power shedding. In case of violation of synchronism and a deep decrease in frequency in a deficient area to the value of the AFC operation, it is possible automatic synchronization and termination of the asynchronous mode.

3.3.3 The termination of the asynchronous run is ensured by the actions of the system emergency automatics, the dispatching personnel of the energy association, and the operating personnel of the power plant. If the stability of intersystem transit communication lines is violated, the asynchronous mode that has arisen should normally be eliminated by the ALAR. If for some reason the ALAR failed and the asynchronous mode continues, the dispatcher gives a command to separate transits, asynchronously operating power systems or nodes at the ALAR installation sites.

When characteristic signs of an asynchronous run appear, the operational personnel of power plants, if the automatic elimination of the asynchronous run of the mode has not worked or is absent, immediately takes measures to restore the normal frequency, without waiting for the order of the power pool manager. This may promote resynchronization.

In parts of the power interconnection, where there is a deep drop in voltage, frequency meters, especially vibration meters, can give unstable or incorrect readings. In these cases, the personnel is guided by the readings of the turbine tachometers.

3.3.4 If, when the normal frequency is reached, the asynchronous operation does not stop, the personnel of the power plant, at which the frequency increased in the event of an accident, makes its further decrease only by order of the dispatcher.

3.3.5 Lowering the frequency at power plants, where it has increased, is carried out by continuous action on the turbine control mechanism both remotely and manually in the direction of lowering the load until the oscillation stops or the frequency decreases, but not lower than 48.5 Hz; it is also allowed (only for the time of resynchronization) to reduce the load by the power limiter.

3.3.6 The increase in frequency in those parts of the power interconnection in which it has decreased is carried out by increasing the load at power plants that have a reserve, with the maximum allowable turbine loading speed according to the instructions of the organization until the oscillations stop or the normal frequency (or the normal number of revolutions according to tachometer readings) is reached.

3.3.7 With an asynchronous course, the operating personnel of the power plant, if it is provided for in the instructions of the organization, raises the voltage to the maximum allowable.

3.3.8 An indicator of the correct actions of the operational personnel is a decrease in the frequency of swings.

As the frequencies in the power pool are equalized, the oscillation period increases, and with a frequency difference of the order of 1.0 - 0.5 Hz, the power plants that have gone out of synchronism are drawn into synchronism.

3.3.9 After the termination of the asynchronous run, the normal load of the power plant is restored (taking into account the actual circuit).

3.3.10 When fluctuations in currents, power and voltage occur, power plant personnel can distinguish synchronous swings from asynchronous. With synchronous swings over communication lines, the power, as a rule, does not change its sign and retains its average value over the period, therefore, with synchronous swings, there is no stable frequency difference in the corresponding parts of the power system. Synchronous oscillations of currents and voltages on generators usually occur around an average value close to the normal (before the appearance of oscillations) value. Most often they are fading in nature. To accelerate the termination of synchronous oscillations of generators, they are unloaded in terms of active power and reactive power is increased without overloading transit links. With synchronous swings through interconnections, the voltage at the power plants of the receiving part of the system increases (reduction of the flow due to the use of a reserve or disconnection of consumers).

3.3.11 The asynchronous operation of one generator in case of loss of excitation due to a malfunction or personnel errors has its own characteristics. In case of loss of excitation, the generator can be left in operation and carry a resistive load. Leaving the generator in operation in this case or its shutdown by protection against loss of excitation is determined by the local conditions of the generator in the network and the possibility of its rapid unloading.

Each power plant draws up a list of generators that allow operation without excitation, indicating the permissible active power and the duration of operation without excitation.

External signs of loss of excitation on generators are:

Consumption by the generator from the mains of a large reactive power, the value of which depends on the voltage in the power system and the active power of the generator;

Decreasing voltage on the busbars of the power plant;

Partial reset of active power and its swing;

Rotor acceleration and its rotation with advanced sliding. In this case, the rotor current disappears or an alternating current with a slip frequency appears in the rotor.

In the event that the generator does not turn off when the excitation is lost, the personnel of the power plant, simultaneously with taking measures to restore the excitation or transfer it to a backup exciter, takes the following measures:

Reduces the active power of the generator up to 40% (it is advisable to use automatic unloading when the protection against loss of excitation is operating using an attachment as part of the ECHSR, or an attachment and a high-speed turbine control mechanism);

Provides voltage increase by increasing the reactive power of other operating generators;

When eating s.n. by tapping from the unit, the generator-transformer provides normal voltage on its buses by transferring power using the AVR device to a backup transformer or by using voltage regulation on s.n. transformers.

If it is not possible to restore excitation within the time specified in the instructions of the organization, the generator is unloaded and disconnected from the network.

3.3.12 When one generator goes out of synchronism with the excitation of the NSS, if there has not been automatic shutdown, immediately disconnects it from the network with simultaneous shutdown of the AGP. The generator out of synchronism can be caused by incorrect actions of the operating personnel (for example, a sharp decrease in the rotor current when the generator is operating with a backup electric machine exciter) or damage to the AVR and, as a result, its incorrect functioning during short circuit and other modes.

The output of the generator from synchronism is accompanied by a change in the values (swings) of currents, voltage, active and reactive power. Due to the uneven acceleration of the changing magnetic field, the out-of-synchronism generator emits a hum. The frequency of the electric current in the network remains practically unchanged.

The operating personnel of the power plant, after turning off the generator that has gone out of synchronism, reports this to the dispatcher, regulates the operating mode of the power plant, determines and eliminates the cause of the violation of synchronism. If the equipment is in good condition (no damage to the generator and other power elements) and automation devices, the turbogenerator is synchronized, connected to the network, and the load is lifted.

In the event of fluctuations in currents, power and voltage on all generators of the power plant and a sharp change in frequency (increase, decrease), the operating personnel act in accordance with the requirements of paragraphs. 3.3.2 -3.3.9.

Separation of the power system

3.4.1 The division of the energy pool into parts and the disappearance of voltage in its individual parts can occur due to:

Deep decrease in frequency and voltage;

Shutdown of transit power lines due to overload;

Incorrect operation of protections or incorrect actions of operational personnel;

Failure of switches;

Asynchronous running and action of dividing protections.

3.4.2 When the energy pool is divided, in some of its parts there is a deficit, and in others - an excess of active and reactive power and, as a result, an increase or decrease in frequency and voltage.

3.4.3 Operating personnel of power plants in the event of the above modes:

Informs the dispatcher of the power association about the outages that have occurred at the power plant, deviations in frequency and voltage, and the presence of overloads of transit power lines;

Takes measures to restore voltage and frequency on the buses of power plants in the divided parts of the system in accordance with the instructions of paragraphs. 3.3.5, 3.3.6. If it is impossible to increase the frequency in the separated system, which is deficient in power, the increase in frequency (after all measures have been taken) is carried out by disconnecting consumers in agreement with the dispatcher;

Removes overloads from transit power lines in case of a threat of violation of static stability;

Provides reliable operation of s.n. mechanisms. up to their allocation to non-synchronous power when the frequency drops to the limits established for a given power plant;

Synchronizes the generators separated during the accident in the presence of voltage from the power pool (or when it appears after the disappearance).

In the absence of bus voltage, the disconnected generators (not included in the s.n. selection circuit) are kept idling or in a state of readiness for a quick turnaround and reconnection to the network with a load set.

At the request of the dispatcher, separate generators or the entire power plant are separated from the part of the power pool, it is synchronized with the deficient part of the power pool.

3.4.4 When voltage appears on the buses of a power plant allocated for operation on a balanced area of \u200b\u200bthe power grid or on a s.n., the operating personnel turn on idle generators for parallel operation. The inclusion can be performed using self-synchronization, if such a method of inclusion is allowed to them and if the s.n. these generators are powered by the selection circuit. Reduced values of voltage and frequency are not the reason for refusal to use the self-synchronization method.

The operating personnel of power plants, the voltage at which was completely lost, when voltage appears, immediately takes measures to turn the mechanisms of s.n. and generators and their inclusion in the network.

3.4.5 The turn of the equipment of the power plant is carried out according to a previously developed scheme with power from generators, power plants operating with allocated s.n. After turning the generators, they are synchronized with the generators of the reserve source, from which the voltage was supplied.

Voltage drop

3.5.1 Automatic regulators of generator excitation systems ensure that the voltage on the buses of power plants is maintained with a droop of 3-5% when the reactive power of the generator changes to the nominal (Q nom) - When the voltage drops at the control points of the generators ARV, in an effort to maintain the voltage on the station buses unchanged, they increase the output of reactive power . At the direction of the dispatcher, the output of Q can be changed by the station personnel in relation to the dispatch schedule by influencing the ACD setting. However, if the voltage at a given control point or at the power facilities of the system drops below a certain value, this voltage will be maintained by using the overload capacity of the generators. At the same time, after a certain time, in accordance with the overload characteristics of the generator, the automation will reduce the rotor current to the nominal value, which can lead to a deeper voltage drop and a possible breakdown of the power system. In case of failure of the limitation, the automation will turn off the generator with overload protection. During this time, after clarifying with the dispatcher the reasons for the voltage drop, the dispatcher takes measures to increase the voltage in the power system (increasing the load of the SC, turning on the batteries of static capacitors, turning off the shunt reactors, changing the transformation ratios of transformers equipped with an on-load tap changer, reducing power flows through the lines). If the use of reactive power reserves turns out to be insufficient, an increase in reactive power loading in power systems with reduced voltage can be obtained by unloading turbogenerators in terms of active power. In a deficient system, this is not recommended due to possible increases in the allowable overflows along the communication line. However, if the voltage drop becomes lower than necessary for s.n. power plants, then active power unloading, together with the disconnection of some consumers, will become necessary.

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

Returning from Europe in 1889, he set about designing a high frequency alternator and soon created a machine whose stator consisted of 348 magnetic poles. This generator made it possible to receive alternating current with a frequency of 10 thousand periods per second (10 kHz). Soon he managed to create an even higher frequency generator and began 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 amount of iron in electromagnetic motors can be significantly reduced, and starting from a certain frequency, it is possible to create electromagnets consisting of windings alone, without any iron in the coils. Motors made from such electromagnets without iron would be extremely light, but in many other respects uneconomical, and the reduction in metal costs would not pay off due to the significant increase in electricity consumption.

Exploring a wide range of alternating current frequencies, initially within the limits that could be applied in a polyphase system (25-200 periods per second), Tesla soon moved on to studying the properties and possibilities of practical use of increased currents (10-20 thousand periods per second) and high (20-100 thousand periods per second) frequencies. To obtain a significantly larger number of periods and significantly higher voltages than could be achieved by the current generators he created high frequency, it was necessary to find and rely on other principles. Well acquainted with the world literature on electrophysics and electrical engineering, Tesla studied the work of the famous American physicist Joseph Henry, who suggested back in 1842 that in some electrical discharges (including the Leiden jar discharge) there are not only "main discharges", but also counter, and each subsequent is somewhat weaker than the previous one. Thus, the existence of a damped two-sided electric discharge was first noticed.

Tesla also knew that eleven years after Henry, the English physicist Lord Kelvin experimentally proved that the electric discharge of a capacitor is a two-way process, continuing until its energy is spent on overcoming the resistance of the medium. The frequency of this two-way process reaches 100 million vibrations per second. The spark between the balls of the spark gap, which seems to be homogeneous, actually consists of several million sparks passing in a short period of time in both directions.

Kelvin gave a mathematical expression for the process of double-sided discharge of a 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. Tesla was also familiar with the works of Anton Oberbank, who observed the phenomenon of electrical resonance, that is, the process of a sharp increase in the amplitude (range) of oscillations when the frequency of an external oscillation approaches the frequency of the natural internal oscillations of the system.

He was well aware of the experiments of Hertz and Lodge, who studied electromagnetic waves. Tesla was especially impressed by the experiments of Heinrich Hertz, which confirmed the theoretical assumptions of James K. Maxwell about 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 the so-called "standing electromagnetic waves", that is, waves superimposed on one another so that in some places they reinforce each other, creating "antinodes", and in others they reduce to zero, creating "nodes".

Knowing all this, Nikola Tesla in 1891 completed the construction of a device that played an exceptional role in the further development of various branches of electrical engineering and especially radio engineering. To create high-frequency and high-voltage currents, he decided to use the well-known property of resonance, that is, the phenomenon of a sharp increase in the amplitude of 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 action of a resonant transformer is based on tuning its primary and secondary circuits into resonance. The primary circuit, containing both a capacitor and an induction coil, makes it possible to obtain alternating currents of very high voltage with frequencies of several million cycles per second. A spark between the balls of the spark gap causes rapid changes in the magnetic field around the primary coil of the vibrator. These changes in the magnetic field give rise to a corresponding high voltage in the winding of the secondary coil, which consists of a large number of turns of thin wire, and 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 greatest value at the moment when the periods of the primary and secondary circuits coincide, that is, when the phenomenon of resonance is observed in these circuits.

Tesla developed a very simple methods automatically charging the capacitor from a low voltage current source and discharging it through an air-core transformer. The theoretical calculations of the inventor showed that even with the smallest values of capacitance and induction in the resonant transformer he created, 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 ability to change the capacitance to change the wavelength of electromagnetic oscillations created by the transformer became 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 problem had to be solved: to find insulation for ultra-high voltage coils. Tesla took up the theory of insulation breakdown and, on the basis of this theory, found the best way to isolate the turns of the coils - to immerse them in paraffin, linseed or mineral oil, now called transformer oil. Later, Tesla once again returned to the development of electrical insulation issues and drew very important conclusions from his theory.

Having barely begun experiments with high-frequency currents, Nikola Tesla clearly imagined the enormous prospects that opened up to humanity with the widespread use of high-frequency currents. The direction of Tesla's work testifies to the unusually versatile conclusions that he drew from his discovery.

First of all, he came to the conclusion that electromagnetic waves play an extremely important role in most natural phenomena. Interacting with each other, they either increase or weaken, or give rise to new phenomena, the origin of which we sometimes attribute to completely different reasons. But not only electromagnetic radiation plays a huge role in a variety of natural phenomena. Tesla, by the intuition of a great scientist, understood the significance of various radiations even 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 a confirmation of his predictions, expressed by him back in 1890.

The enormous importance of alternating currents in the development of industry, which finally received the electric motor it needed, became clear to Nikola Tesla at the first acquaintance with the advantages of three-phase current, which requires only three wires to transmit it. For Tesla already at that time it was undeniable that a method of transmitting electricity should be discovered without wires at all, using electromagnetic waves. This problem attracted Tesla's attention and became the subject of his studies as early as the end of 1889.

However practical use high-frequency currents for a wide variety of purposes required the study of at first glance the most diverse, unrelated issues. It was these experiments on a large scale that Nikola Tesla began to conduct in his laboratory.

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

Nikola Tesla's thought process was extremely original. It is known, he reasoned, that direct current of low voltage (up to 36 volts) does not have harmful effects on a person. As the voltage increases, the possibility of damage increases rapidly.

With an increase in voltage, since the resistance of the human body is practically unchanged, the current strength also increases and reaches an alarming value at 120 volts. Higher voltage becomes dangerous for human health and life.

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

Step by step, Tesla investigated the effect of alternating electric current on a person at different frequencies and voltages. He experimented on himself. First, through the fingers of one hand, then through both hands, and finally through the whole body, he passed currents of high voltage and high frequency. Studies have shown that the effect of electric current on the human body consists of two components: the effect of current on tissues and cells by heating and the direct effect 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 stops at a frequency of more than 700 periods, similar to how a person’s hearing does not respond to vibrations over 2 thousand per second, and the eye does not respond to vibrations beyond the visible spectrum colors.

Thus, the safety of high-frequency currents even at high voltages was established. Moreover, the thermal effects of these currents could be used in medicine, and this discovery of Nikola Tesla was widely used; diathermy, UHF treatment and other methods of electrotherapy are a direct consequence of his research. Tesla himself developed a number of electrothermal devices and devices for medicine, which were widely used both in the USA and in Europe. His discovery was then developed by other eminent electricians and physicians.

Once, while experimenting with high-frequency currents and bringing their voltage to 2 million volts, Tesla accidentally brought a copper disk painted with black paint closer to the equipment. At the same moment, a thick black cloud enveloped the disk and immediately rose up, and the disk itself shone, as if some invisible hand had scraped off all the paint and polished it.

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

“It is curious,” he thought, “whether these currents will also affect human skin, whether it will be possible with their help to remove various paints that are difficult to remove from it.”

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 a small rash from the skin of the face, clean the pores, and kill the microbes that always cover the surface of the human body in abundance. Tesla believed that his lamps had a special beneficial effect not only on the retina, but also on the entire human nervous system. In addition, Tesla lamps cause air ozonation, 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 regular congress of the American Electrotherapeutic Association in Buffalo.

In the laboratory, Tesla passed currents of 1 million volts through his body at a frequency of 100 thousand periods per second (the current reached a value of 0.8 amperes). But, operating with currents of high frequency and high voltage, Tesla was very careful and demanded that his assistants comply with all the safety rules he himself developed. 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 in order to prevent the possibility of current flowing through the heart. Many other rules pioneered by Tesla have become part of modern high voltage safety precautions.

Having created a variety of equipment 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 possibility of practical use of high frequency and high voltage currents. His works covered the whole variety of phenomena, ranging from the generation (creation) of high-frequency currents to a detailed study of various possibilities for their practical use. With each new discovery, more and more problems arose.

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

Soon he accumulated a huge amount of facts, which made it possible to proceed to generalizations. However, Tesla's caution forced him to check each of his statements dozens and hundreds of times. He repeated each experience hundreds of times before drawing any conclusions from it. The unusualness of all the discoveries of Nikola Tesla and his enormous authority attracted the attention of the leaders of the American Institute of Electrical Engineers, who again, like three years ago, invited Tesla to give a lecture on his work. Tesla chose the topic: "Experiments with alternating currents of very high frequency and their use for artificial lighting."

According to the tradition that has been established since the first years of the institute's existence, a limited number of invitations were sent out only to the most outstanding electrical engineers. Before such a select audience on May 20, 1892, Tesla gave one of his most inspirational lectures and demonstrated the experiments he had already carried out in his laboratory.

There is nothing that could attract the attention of man to a greater extent and would deserve to be the subject of study than nature. To understand its huge mechanism, to discover its creative forces and to know the laws that govern it is the greatest goal of the human mind, - with these words Tesla began his speech.

And now he is already demonstrating to the audience the results of his research in a new, yet unstudied area of high-frequency currents.

The 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 wonderful experience. He puts forward an ingenious position on the possibility of transmitting electricity without wires and, as proof, makes both ordinary incandescent lamps and lamps specially created by him without filaments glow inside, introducing them into an alternating high-frequency electromagnetic field. “Lighting with lamps of this kind,” says Tesla, “where the light does not arise from the heating of the filaments by the flowing current, but due to special vibrations of the molecules and atoms of the gas, will be easier than lighting with modern incandescent lamps. Illumination of the future, - emphasized the scientist, - is illumination by high-frequency currents.

Tesla dwelled in particular detail on the description of his resonant transformer as a source of waves of very high frequency and again emphasized the importance of the discharge of a capacitor in creating such oscillations. Tesla correctly assessed the great future of this most important part of modern radio equipment. He expressed this idea in the following words:

I think that the discharge of the capacitor will play an important role in the future, since it will not only make it possible to receive light more in a simple way in the sense indicated by the theory I have outlined, but will be important in many other respects.

After detailing the results of experiments with high-frequency currents produced by a resonant transformer, Tesla concluded the lecture with words that testify to his clear understanding of the value of further study of phenomena on which his work had barely lifted the veil of mystery:

We are passing with unfathomable 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 currently known. And when light is obtained from the environment around us, and when all forms of energy are obtained effortlessly from their inexhaustible source in the same way, humanity will advance with gigantic strides.

The mere contemplation of this glorious prospect lifts our spirits, strengthens our hope, and fills our hearts with the greatest joy.

To thunderous applause, Tesla ended his remarkable performance. The extraordinary nature of everything shown and the particularly bold conclusions of the scientist, who saw the revolutionary consequences of his discoveries, amazed the audience, although not everyone understood the content of the lecture as deeply as Nikola Tesla would have liked.