RU2663545C1 - Optical measurement of variable and constant currents in high-voltage networks - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention relates to optical instrumentation, or more precisely to optical polarization devices, in which the Faraday effect is used. Invention will be used in the electric power industry, for example in high-voltage networks of various classes, digital substations and other electrical installations. Proposed device comprises a light source, a multimode optical fiber, a Faraday cell, a second multimode fiber, a photodetector, an electronic unit with an indicator of measurement results. For measurement of alternating and direct current, the first polarizer of the Faraday cell is made in the form of a Wollaston prism, the second polarizer is made as a ring from a polaroid film. Outgoing from the Wollaston prism, the rays pass through the inner opening of the second polarizer. Active element of the Faraday cell is made in the form of an optical glass cylinder with polished bases. On one of the bases is a mirror coating. Double-transmitted polarized light beams pass through a second polarizer whose transmission plane is at an angle ±45° with respect to the transmission planes of the first polarizer. After the second polarizer, two light-gathering lenses, two multimode optical fibers, two photodetectors, and also two linear photodetector amplifiers are installed in the two bunches separated by the Wollaston prism. As an embodiment, the high voltage line conductor fragment consists of a set of parallel conductors connected in parallel, made in the form of a solenoid that covers the Faraday cell cylinder and contains n turns where 1≤n≤6.

EFFECT: thanks to the presence of the Wollaston prism, the proposed device is universal, that is, it measures alternating or direct current.

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Description

The invention relates to optical instrumentation, and more specifically to optical polarization devices, which use the effect of rotation of the plane of polarization of light by a substance located in a longitudinal magnetic field (Faraday effect). The invention can be used in the electric power industry, for example, in high voltage networks of various classes, in electric transport networks, metallurgy and other electrical installations.

Usually, electromagnetic current transformers containing a primary winding of one or two turns (a fragment of a high-voltage line conductor) and a secondary winding containing a large number of turns, which is connected to control equipment located at zero ground potential, are used to measure alternating current in high-voltage networks. Between the primary and secondary windings there is an insulating material, for example, special oil or SF6. The main disadvantage of such transformers is the high probability of breakdown of insulation between the windings, which threatens the risk of fire.

An alternative to traditional electromagnetic current transformers are optoelectronic current meters. These meters are based on the phenomenon of rotation of the plane of polarization of light by a transparent substance located in a longitudinal magnetic field relative to the direction of light propagation, discovered by M. Faraday [1]. Research in the field of creation of optoelectronic current meters has been underway for a long time [2].

The main node of such devices is the so-called Faraday cell, which consists of two linear polarizers, between which an active transparent substance is installed, for example, glass with a large Verdet constant, placed in a magnetic field so that the magnetic field lines of the field coincide with the direction of propagation of linearly polarized light in the substance.

Under the action of the longitudinal magnetic field lines of the high-voltage line conductor fragment, the active substance acquires the ability to rotate the plane of polarization of linearly polarized light by an angle

where: H is the value of the longitudinal magnetic field acting on the active element of the Faraday cell;

V is the Verdet constant of the material of the active element;

- длина пути, пройденного пучком света в активном элементе;

- the length of the path traveled by a beam of light in the active element;

β is the angle between the direction of light propagation and the direction of the lines of force of the magnetic field;

N is the number of turns of a fragment of a conductor with current;

i is the current flowing along the conductor;

k is a design coefficient that takes into account the distance to the conductor, aspect ratio, conductor cross-section and averaging of the magnetic field at various points of the active element.

From the measured value of the angle of rotation of the plane of polarization α, it is possible to determine the magnitude of the current i flowing through a conductor fragment

- постоянные величины для конкретной конструкции ячейки Фарадея.where N, k, V and

- constant values for the specific design of the Faraday cell.

Devices are known in which an optical fiber is used as the active substance of a Faraday cell. A typical representative of such devices is a current measuring system according to the US patent [3]. It contains a light source and a multimode optical fiber, a polarizer, a coil of single-mode optical fiber, a second polarizer, the transmission plane of which is an angle of ± 45 ° with the transmission plane of the first polarizer, the second multimode optical fiber, a photodetector, and an electronic unit.

During the passage of current i through a fragment of a conductor of a high-voltage line, a magnetic field arises around it, the lines of force of which coincide with the turns of a coil of optical single-mode fiber, and therefore coincide with the direction of propagation of light rays. As a result, the effect of rotation of the plane of polarization of linearly polarized light (the Faraday effect) occurs in an optical fiber.

However, it is known that the principle of operation of any optical fiber is based on the phenomenon of total internal reflection of light, in which a phase difference δ [1] inevitably arises between mutually orthogonal components of polarized light and the light becomes elliptically polarized. The magnitude of the phase difference δ and the degree of ellipticity depend on the orientation of the plane of incidence of light at the interface between the core of the optical fiber and its cladding and the angle of refraction during each event of total internal reflection of light inside the optical fiber. During the passage of linearly polarized light through a single-mode fiber, the angle of incidence of light at the interface between the fiber core and its cladding is close to 90 ° and the resulting phase difference δ is not large compared with what is observed in a multimode optical fiber. But she is always there. In addition, when bending an optical fiber, mechanical loads inevitably arise in it, which lead to the appearance of birefringence.

Therefore, any optical fiber can be represented as a set of phase plates with different directions of the main axes, converting linearly polarized light to elliptically polarized.

During the propagation of linearly polarized light in an optical fiber, a random transformation of the state of polarization of light occurs, and instead of linearly polarized light, at the output of the optical fiber we obtain partially polarized light (if the fiber is single-mode) or completely non-polarized light (if the fiber is multi-mode).

As a result, simultaneously with the effect of rotation of the plane of polarization by an angle α in a single-mode fiber, partial depolarization of light occurs with a depolarization coefficient Δp.

Consequently, the active element of the Faraday cell, made in the form of a single-mode optical fiber, can be represented by a transformation matrix by the effect on linearly polarized light

where: p = 1-Δp is the degree of polarization of light;

α is the angle of rotation of the plane of polarization of light by an optical fiber under the influence of a magnetic field.

The light intensity I after the Faraday cell can be found from the equation

- искомый вектор Стокса;Where

- the desired Stokes vector;

is the Stokes vector of unpolarized light with the intensity I _{O of the} light source;

- a light conversion matrix by a first linear polarizer, the transmission plane of which, for example, is horizontal;

- light conversion matrix by a second linear polarizer, the transmission plane of which is an angle of 45 ° with respect to the first polarizer.

After multiplying the matrices (5-7), we find the desired first Stokes parameter proportional to the light intensity

An alternating current with a frequency of 50 Hz flows through a fragment of a conductor of a high-voltage line, therefore, the magnetic field H is also variable, and at the output of the Faraday cell, the photodetector senses light that varies according to the law

where: α _max - the maximum angle of rotation of the plane of polarization corresponding to the moment of maximum current:

ω = (50 ± 1) Hz - network frequency.

From equation (9) shows that in the absence of current i in the network, when H = 0 and α = 0, the light intensity I = 0,25 I ₀ and the spectrum of the photodetector signal is present only the constant component U _{= =} 0,25 I ₀ . When an alternating current conductor i = i _max sinωt flows through a fragment of a conductor, an alternating component appears in the spectrum of the photodetector signal

The signal conversion unit calculates the ratio

and then the desired current i in the conductor fragment

From equation (12) it is seen that the degree (level) of polarization of light p directly affects the value of the angle of rotation of the plane of polarization α and, therefore, the result of measuring the current i.

It is known that a multimode optical fiber almost completely depolarizes light. Polarized light p = 1 turns into unpolarized light p = 0 and therefore a multimode optical fiber is unsuitable for use as an active element of a Faraday cell. A single-mode optical fiber (fiber diameter of about 4 μm) with a small length partially retains the polarization, however, there are a number of significant difficulties in introducing a light beam into such a fiber with a sufficient amount of luminous flux. In addition, during the manufacture of an optical fiber coil, fiber bending occurs, in which uncontrolled mechanical stresses appear in the fiber, which leads to even more depolarization of light and, ultimately, to significant uncontrolled errors in measuring AC current.

Therefore, the advertised optical current meters, in which coils of single-mode optical fiber are used as the active element of the Faraday cell, have the significant disadvantages listed above.

A more advanced device and the closest prototype is an optical meter of alternating current in high-voltage networks [4].

The known optical meter of alternating current in high voltage networks [4] contains a light source 1 (Fig. 1), a multimode optical fiber 2, the end of which is the focal plane of the collimating lens 3 installed behind it, the first polarizer 4, the active element of the Faraday cell 5, made of optical glass located in a longitudinal (relative to the direction of light) magnetic field created by a fragment of a conductor with current 6, a second polarizer 7, the transmission plane of which is an angle of ± 45 ° with the transmission plane ervogo polarizer 4, the collecting lens 8, and the second multimode fiber 9, a photodetector 10. The photodetector 10 is connected to an amplifier, which is located in the signal conversion unit 11. Active element 5 Faraday cell is formed as a quadrangular prism 5 TF5 glass having a high Verdet constant. The first base of the prism 5, on which light is incident, is polished and a mirror-like coating in the form of a rectangular strip is applied on its surface in the center. Another base of prism 5 is divided into three equal rectangular zones. On both sides of the central zone there are two polished surfaces with mirror coatings that make up equal angles with the plane of the central zone

where: D is the diameter of the collimated beam of light;

h is the height of the quadrangular prism 5.

A fragment of a network conductor in the form of a flat bus 6 is located near the wide face of prism 5. Light from a source 1 is transmitted through a multimode optical fiber 2 to the focal plane of a collimating prism 3. A diverging light beam emerging from optical fiber 2 is converted by lens 3 into a collimated beam with a diameter D. Further the light passes through the first polarizer 4 and becomes linearly polarized, the azimuth of light polarization is parallel to one of the side faces of the prism 5, for example, a wide face. The linearly polarized collimated light beam passes through the prism 5 four times, passes the polarizer 7, the transmission plane of which is ± 45 °, and the lens 8 is collected at the end of the optical fiber 9. Next, the light enters the photodetector 10.

If the current i on the bus 6 does not pass and the magnetic field around the bus H = 0, then the light intensity I, perceived by the photodetector 10,

where: I ₀ - the intensity of the light incident on the polarizer 4;

R- Light reflection coefficient from three mirror surfaces of prism 5.

If alternating current i = i _max sinωt of the frequency of the network ω flows through bus 6, then the photodetector 10 picks up light intensity

and converts it into an electrical signal

which in the electronic unit 11 is formed in the form of a constant component U ₌ U ₀ and a variable component U _~ = U ₀ [sin (2α _max sinωt)]. In the electronic unit 11, the ratio is calculated

and then the desired current i flowing along the bus 6 is calculated according to the formula

where N = 1 is the number of turns of the tire 6;

V is the Verdet constant of the glass prism 5;

- длина пути, пройденного света в призме 5;

- the length of the path traveled by the light in the prism 5;

M is a coefficient characterizing the efficiency of using the longitudinal component of the magnetic field of the tire 6.

Analyzing formulas (16) and (17), we find that the ratio of the variable component U _~ to the constant component U _{= of} the photodetector 10 signal at small angles α is proportional to the desired current value i and does not depend on a change in the value of U _O , that is, Q is a normalized value.

Tests have shown that if an alternating current flows through a fragment of a conductor 6, then using a well-known optical AC meter [4], it is possible to measure current, for example, in the range from 0 to 600 A with an accuracy of ± 0.5 A.

A significant drawback of the known optical AC meter in high voltage networks [4] is its practical unsuitability for operation in DC networks.

So, if a constant current flows through bus 6 (Fig. 1), then at the output of photodetector 10 we get a signal that varies according to the law

From formula (19) it can be seen that at constant current there are no signs for separation of the constant component of the signal U ₀ , independent of the angle of rotation of the plane of polarization of light α and component U ₀ sin2α, depending on the change in the angle α.

In this case, for angle α and current i, we can write

It can be seen from expressions (20) and (21) that any uncontrolled change in the constant component of the photodetector signal leads to errors in measuring the angle α and, accordingly, the current i.

The use of special stabilizers of the power supply of the light source 1 and the power of the signal amplifier of the photodetector 10 does not completely eliminate the errors of direct current measurement. For example, changes in the magnitude of the signal of the photodetector 10 can occur as a result of severe climatic conditions of use.

A new optical meter of alternating and direct current is proposed, free from the mentioned drawback.

An optical meter of alternating and direct current in high-voltage networks contains a light source and a multimode optical fiber installed sequentially along the rays of light, the end of which is in the focal plane of the collimating lens installed behind it, the first polarizer, the active element of the Faraday cell made of glass with a high constant value Verde, located in a longitudinal magnetic field of a conductor fragment with a high-voltage network current, is a second polarizer, the transmission plane of which was it has an angle of ± 45 ° with the plane of polarization of the first polarizer, a light-collecting lens, a second multimode optical fiber, a photodetector, an electronic unit with a signal converter, a computer, and an indicator of the measurement results. In order to measure both alternating and constant currents in high-voltage networks, the first polarizer is made in the form of a Wollaston prism with an angle of dilution of polarized rays

where: D is the diameter of the working light beam;

L is the path length of the light beam passed from the Wollaston prism to the second polarizer.

The active element of the Faraday cage is made in the form of a glass cylinder with polished bases, one of which is coated with a mirror. The second polarizer is made in the form of a ring, the inner diameter of which is larger than the diameter D of the working light beam, and is installed so that two light beams emerging from the first polarizer pass through the internal holes of the second polarizer. After the second polarizer, two identical light-collecting lenses, two identical multimode optical fibers, two identical photodetectors, and two identical linear photodetector signal amplifiers, respectively, are installed in two beams of light separated and reflected from the mirror surface of the cylinder.

All optical elements related to the Faraday cell, that is, a collimator lens, a Wollaston prism, a glass cylinder, a second ring-shaped polarizer that collects lens light, are mounted in a single monolithic body of dielectric material. A fragment of a conductor of a high-voltage network consists of a set of separate conductors connected in parallel, for example, buses, and is made in the form of a solenoid, covering the active element of a Faraday cell, consisting of n turns, where 1≤n≤6.

In FIG. 1 is a structural diagram of a known optical AC meter in high voltage networks [4].

In FIG. 2 shows a structural diagram of the proposed optical meter AC and DC in high voltage networks.

The proposed optical meter of alternating and direct current in high-voltage networks (Fig. 2) contains a light source 1, for example, in the form of a semiconductor quantum generator module, with a maximum radiation spectral density μ _{(λ) max} ≈ 532 nm. And the multimode optical fiber 2, the collimating lens 3, the first polarizer in the form of a Wollaston 4 prism, the active element of the Faraday cell in the form of a glass cylinder 5, installed in the longitudinal magnetic field of a fragment of the conductor 6 with the high-voltage network current, the second polarizer 7, installed sequentially along the rays of light, made in the form of a ring. The polished end face of the optical fiber 2 is mounted at the focus of the collimating lens 3. The dilution angle of the polarized rays of the Wollaston prism 4

2β≥arctg (2D / L),

where: D is the diameter of the working light beam after the collimation lens 3;

L - The path length of the light beam passed from the Wollaston prism to the second polarizer.

The active element of the Faraday cell is made in the form of a glass cylinder 5 with polished bases. One of the polished bases (the opposite of the one onto which the light is incident) is coated with a mirror. The second polarizer 7 is made of a polaroid film in the form of a ring, the inner diameter of which is larger than the diameter D of the working light beam and is installed so that two light beams emerging from the first polarizer 4 pass through the inner hole of the second ring-shaped polarizer 7. After the second polarizer 7 in two separated two beams of light reflected from the mirror surface of the second base of the glass cylinder 5, respectively, are equipped with two identical collecting lenses 8, two identical multimode optical fibers 9 and two and entichnyh photodetector 10.

The light source 1, the photodetectors 10 and the ends of the optical fibers 2, 9 are mounted in a separate electronic unit 11, where there are two identical linear amplifiers 12 of the signals of the photodetectors 10, signal converters 13, 14, a computer 15 and an indicator of the results of measurements of currents 16.

All optical elements related to the Faraday cage are housed in a single assembly consisting of a base 17, an insert 18 and a cup 19 with a cover 20. The assembly parts are made of diamagnetic and dielectric material, for example, fiberglass. The base 17 has a flange with which the assembly of the Faraday cage is attached to the upper metal flange 21 of the high-voltage insulator (not shown in Fig. 2)

A fragment of the conductor 6 of the high-voltage line is made in the form of a solenoid and covers the Faraday cell in the place where the glass cylinder 5. The solenoid 6 is attached by brackets directly to the upper flange 21 of the insulator, but so that between the inner surface of the solenoid 6 and the glass 19 of the Faraday cup air gap. Such fastening prevents mechanical action on the Faraday cell from the side of the conductor fragment (solenoid) 6 in cases of inrush currents in the high-voltage line or the impact of wind gusts on it.

Since with increasing cross-section of a fragment of a conductor of a high-voltage line, restrictions arise in the allowable bending radii of the conductors, the fragment of conductor 6 is made in the form of a solenoid, which consists of separate thin conductors, for example, rectangular buses connected in parallel. Thinner conductors allow a smaller bending radius than thick ones. Therefore, a set of individual thin conductors interconnected in parallel allows, without violating GOST for conductors, to produce compact solenoids of small diameters and large cross sections.

This design of a fragment of a conductor of a high-voltage line makes it possible to increase the magnetic field strength in the region of the active element of a Faraday cage and thereby increase the sensitivity and accuracy of current measurement.

The proposed optical meter for alternating and direct current in high voltage networks operates as follows:

The light from the source 1 is transmitted through a multimode optical fiber 2 to the focal plane of the collimating lens 3. The diverging light beam emerging from the optical fiber 2 is converted by the lens 3 into a collimated light beam of diameter D. Then the light passes through the first polarizer in the form of a Wollaston 4 prism and is separated, for example, in the drawing plane (Fig. 2) into two linearly polarized beams whose polarization planes are mutually orthogonal. The separation angle of 2β polarized beams by prism 4 satisfies condition (22). Separated linearly polarized light beams pass through the glass cylinder 5, which is located in the center of the solenoid 6, are reflected from the mirror surface of the base of the cylinder 5, pass through the glass cylinder 5 again, and the second ring-shaped polarizer 7 passes from both sides in diameter. After polarizer 7, each of the two light beams lenses 8 are collected at the ends of multimode optical fibers 9 and are fed to the photosensitive layers of the photodetectors 10.

The collimated monochromatic light beam of source 1, as a rule, is partially polarized with an arbitrary azimuth of polarization ε, therefore, its radiation can be represented by the Stokes vector

where: I ₀ - light intensity of source 1;

p is the degree of polarization of light.

The multimode optical fiber 2 can be represented by the matrix of an ideal depolarizer by its effect on polarized light

Therefore, the collimated light beam after lens 3, which falls on the prism of Wollaston 4, will not be polarized and can be represented by a vector

If the Wollaston prism 4 is installed so that the polarized light beams are separated by it in the horizontal plane, then the plane of polarization of one of them is horizontal and the other is vertical. In this case, the intensities of light beams after the second polarizer can be found from the equation

- вектор Стокса света, падающего на призму Волластона 4;Where:

- Stokes vector of light incident on the prism of Wollaston 4;

- матрица преобразования призмы Волластона;

- Wollaston prism transformation matrix;

- матрица преобразования стеклянного цилиндра 5, на который действует магнитное поле фрагмента проводника 6;

- the transformation matrix of the glass cylinder 5, which is affected by the magnetic field of the fragment of the conductor 6;

- матрица преобразования поляризатора 7.

- polarization conversion matrix 7.

находим первые параметры Стокса пучков света, характеризующие их интенсивности I₁, I₂, когда по соленоиду 6 течет постоянный ток и на цилиндр 5 действует постоянное магнитное поле:After multiplying the transformation matrices of the optics and the original vector

we find the first Stokes parameters of light beams characterizing their intensities I ₁ , I ₂ when a direct current flows through solenoid 6 and a constant magnetic field acts on cylinder 5:

Photodetectors 10 convert light beams with intensities I ₁ and I ₂ into electrical signals

Line amplifiers 12 amplify these signals. The adder 13 sums the signals

and block 14 subtracts the signals

Calculator 15 finds the relation

value of the measured direct current

- постоянная величина, зависящая от числа витков N соленоида 6, от коэффициента использования магнитного поля k, от постоянной Верде V стекла цилиндра 5 и длины пути L пучка света в цилиндре 5.Where:

- a constant value, depending on the number of turns N of the solenoid 6, on the coefficient of use of the magnetic field k, on the Verdet constant V of the glass of the cylinder 5 and the path length L of the light beam in the cylinder 5.

If an alternating current of frequency ω flows along solenoid 6 and the magnetic field inside the solenoid 6 is also variable H = H _max Sinωt, then photodetectors 10 will perceive light intensity

Accordingly, the output of the linear amplifiers 12 will be electrical signals

The variable components of the frequency signals ω are out of phase, therefore, at the output of the adder 13 we get the same constant component 2U ₀ , as in the considered case for direct current (31), and at the output of the subtraction unit 14 we get the signal difference in the form of a variable component

After detection and smoothing, a signal characterized by dependence (39) can be represented by dependence (32).

Next, the calculator 15 also finds the ratio Q by the formula (33) and the value of the flowing alternating current through the solenoid 6 according to the formula (34).

The proposed device has several advantages.

Firstly, setting the Wollaston prism as the first polarizer allows one to obtain a normalized signal ratio Q, independent of some change in the intensity of radiation I _{0 of} source 1 or the amount of conversion of light into an electrical signal U ₀ . This normalization of the signals does not depend on the type of current flowing through the solenoid 6. Therefore, the proposed optical current meter is a universal device.

Secondly, the implementation of the second polarizer 7 in the form of a ring, and the first polarizer in the form of a Wollaston prism with an angle of dilution of polarized light beams of diameter D by an amount

2β≥arctg (2D / L), allowed to create a compact Faraday cell with a double passage of light beams through a glass cylinder 5.

Thirdly, the execution of a fragment of a conductor of a high-voltage line from a set of separate conductors connected in parallel to each other made it possible to bring them as close to cylinder 6 as possible and create a compact solenoid 6 with a sufficient total cross-section of conductors for passing alternating or direct currents up to 600 A in the variant of an optical current meter networks, 5000A in versions of the optical current meter in high-voltage lines of high and ultra-high classes, as well as at the same time achieve maximum efficiency olzovaniya magnetic field conductor 6.

Fourth, choosing the length of the cylinder 5 and the number of turns of the solenoid 6, you can choose the optimal mode of operation of the proposed optical meter of alternating or constant currents. For example, if solenoid 6 has 4 turns and is connected to a distribution network (U _max = 35 kV and i _max = 600 A), the cylinder length is 70 mm, then the maximum measured angle of rotation of the polarization plane of the Faraday cell ± α _max ≈ 9.8 °, which allows to achieve a current measurement sensitivity of ± 0.08A. This is a great achievement for this class of current meters.

INFORMATION SOURCES

1. Lansberg G.S. Optics, 4th ed. M., 1957, with 618-620.

2. Zubkov V.P., Krasina A.D. Optoelectronic measurement methods in high voltage installations: (review). - M .: Informenergo. 1975.156 s.

3. US patent No. 3605013, G01R 15/246.

4. RF patent for utility model No. 171401 dated November 30, 2016. “Optical meter of alternating current in high-voltage networks”.

Claims (4)

1. An optical meter for alternating and direct current in high-voltage networks, containing a light source and a multimode optical fiber installed sequentially along the rays of light, the end of which is in the focal plane of the collimating lens installed behind it, the first polarizer, the magneto-optical active element of the Faraday cage, located in the longitudinal in relation to the direction of light propagation, the magnetic field created by a fragment of a conductor with a high-voltage network current, a second polarizer, a plane the lowering of which is an angle of ± 45 ° with the transmission plane of the first polarizer, a light-collecting lens, a second multimode fiber, a photodetector, an electronic unit with a signal converter, a calculator and an indicator of the measurement results, characterized in that for measuring AC and DC current the first polarizer is made in the form Wollaston prisms with the angle of dilution of polarized rays

where: D is the diameter of the working light beam; L is the path length of the light beam passed from the Wollaston prism to the second polarizer, the active element is made of optical glass in the form of a cylinder with polished bases, one of which is coated with a mirror coating, the second polarizer is made in the form of a ring, the inner diameter of which is larger than the diameter D of the working of the light beam and is installed so that the light beams emerging from the first polarizer pass through the internal hole of the second polarizer, after the second polarizer, in two separated by a Wollaston prism and are reflected x two light-collecting lenses, two multimode optical fibers, two photodetectors, and two linear photodetector signal amplifiers, respectively, are installed from the mirrors of the active element to the light beams. 2. The optical meter of alternating and direct current according to claim 1, characterized in that the fragment of the high-voltage line conductor consists of a set of separate conductors connected in parallel, made in the form of a solenoid, covering the active element of the Faraday cage, and contains n turns, where 1≤n≤ 6.

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