RU2752341C1 - Optical dual-channel current meter - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to optical instrument manufacture, in particular, to polarisation apparatuses wherein the Faraday effect is used to measure the electric current in high-voltage networks. Substance: the optical dual-channel current meter is comprised of two measuring channels: precise and rough. Each channel comprises a light source, an optical fibre, a collimator, a first polariser, a glass prism, a second polariser, the transmission plane whereof constitutes ±45° with the transmission plane of the first polariser, a second optical fibre, and a photodetector. Both glass prisms are installed in a coaxial magnetic field of a complete coil of a conductor segment, made, e.g., of a copper wide bus in form of one or two coils. The path taken by the polarised light in the glass of the precise channel is several times longer than the path taken by the light in the rough channel.EFFECT: increased current measurement range with high measurement accuracy, provided is also a signal for positive action of the relay protection at short-circuit currents.2 cl, 9 dwg

Description

The invention relates to optical instrumentation, or rather to optical polarizing devices, in which the Faraday effect is used to measure alternating electric current in high-voltage networks.

Currently, the most common current meters in high-voltage networks are electromagnetic measuring current transformers (ITTE) [1], which contain a primary winding of one or two turns of a fragment of a high-voltage line conductor, a magnetic core made of transformer iron and one or two secondary windings. An insulating material such as transformer oil or SF6 gas is located between the primary and secondary windings.

The secondary winding is necessarily loaded with a complex resistance, through which the rated current of the secondary winding flows (usually 1, 2 or 5A).

If the voltage of the network is 330 kV and higher, then the ITFC is made in cascade, that is, with several magnetic circuits, in which the secondary winding of the previous magnetic circuit is the primary winding of the next one.

This reduces the requirement for insulation between the windings.

Significant disadvantages of ITTE are:

- high fire hazard due to possible electrical breakdowns of insulation between the windings;

- saturation of the magnetic circuit of the aperiodic component of the short-circuit current;

- significant consumption of copper for the manufacture of secondary windings;

- the inevitable consumption of electricity in the secondary windings;

- influence on the accuracy of current measurement of the load value and the number of measured current recorders connected to the secondary winding;

- analog signal characterizing the measured current;

- large dimensions, weight and cost, especially at network voltages of 330 kV and more.

As an alternative to ITTE, there are a number of devices for measuring current, the operating principle of which is based not on the principle of electromagnetic current transformation, but on other physical principles.

The most convenient and promising are optical current meters, the principle of operation of which is based on the phenomenon of rotation of the plane of polarization of linearly polarized light in a magnetically sensitive isotropic substance (glass) located in a longitudinal (coaxial) magnetic field (based on the Faraday effect).

The essence of the effect is as follows. Linearly polarized light can be represented as the sum of two circularly polarized components of the same amplitude. Under the action of a longitudinal magnetic field in substances such as glass, birefringence occurs for the circularly polarized components of the left and right circulation, and a phase difference arises between these components

where V _l , V _pr - phase velocities of propagation of the left and right waves;

n _l , n _pr - refractive indices, respectively, for the left and right circularly polarized components;

L is the path traversed by the polarized light in the substance along the magnetic field strength;

λ ₀ is the wavelength of light.

If the magnetically sensitive glass is isotropic, that is, it does not have linear birefringence [2], then at the exit from the glass the circular polarization of both components is retained and when they are added, linearly polarized light is obtained again, but with a changed polarization azimuth by an angle

- величина напряженности продольного магнитного поля, действующего на стекло;where:

- the magnitude of the strength of the longitudinal magnetic field acting on the glass;

V is the Verde glass constant;

L is the path traveled by the polarized light in the glass;

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

N is the number of turns of the wire fragment;

i is the current flowing through the fragment of the conductor;

k is a design factor that takes into account the distance from the glass to the current conductor and the averaging of the magnetic field strength at different points of the glass.

From formulas (1, 2), it can be seen that two methods can be used to measure the current i flowing through the conductor of a high-voltage line: a method based on measuring the azimuth of linear polarization α or measuring the phase difference δ ₀ .

Most often, the first method is used, in which linearly polarized light is directed to a magnetically sensitive element (glass) located in a longitudinal magnetic field, and at the exit from the glass the change in the azimuth of the linear polarization of light is measured, which is proportional to the magnetic field strength, and, therefore, to the measured current i ...

The simplest device is known [3] that implements this method. It contains a collimated light source, a first linear polarizer, a glass rod with polished ends, and a second linear polarizer. Let the transmission plane of the second polarizer make an angle of ± 45 ° with the transmission plane of the first polarizer, and the glass rod is placed in the center of the solenoid, through which the measured alternating current of the mains frequency ω = 50 Hz flows

According to the effect on linearly polarized light, a glass rod can be represented by a rotator matrix [4]:

where α _max is the maximum amplitude of the angle of rotation of the plane of polarization of light, in accordance with formula (3).

The light intensity I at the output of the device can be found from the equation

вектор Стокса неполяризованного света источника интенсивностью I₀;where

Stokes vector of unpolarized light source with intensity I ₀ ;

[M _P ] _{45 °} and [M _P ] _{0 °} are tabular matrices for ideal linear polarizers [4] with transmission planes, respectively, 0 ° and 45 °.

After multiplying the transformation matrices (5), we find the first parameter of the Stokes vector, which characterizes the light intensity I, after the second polarizer

The ratio Q of the variable component to the constant component of light I carries information about the angle of rotation α and the magnitude of the current i, namely:

However, such simple devices are not used in high-voltage networks due to the complexity of supplying light to a glass rod under high voltage. It is tempting to use fiber optics as a magnetically sensitive element of the Faraday cell. Known devices in which fiber optic fibers are wound in the form of coils and put on fragments of conductors with a high-voltage line current so that the turns of the optical fibers coincide with the direction of the magnetic field lines of the fragment of the conductor [5].

The main disadvantage of such devices is the significant depolarization of linearly polarized light in optical fibers. 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 inevitably occurs between the mutually orthogonal components of linearly polarized light and the linearly polarized light becomes elliptically polarized.

The magnitude of the phase difference and the degree of ellipticity depend on the orientation of the plane of polarization of the incident light relative to the plane of the interface between the fiber core and its cladding, as well as on the angle of refraction at each event of internal reflection inside the fiber. In addition, when the fibers are bent, mechanical loads inevitably appear in them, which lead to the appearance of linear birefringence and to an additional phase difference. Consequently, optical fibers are anisotropic. Any optical fiber can be represented as a set of phase plates with different directions of the main axes, converting linearly polarized light into elliptical.

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

Consequently, a magnetically sensitive element made in the form of a single-mode fiber light guide, according to the effect on linearly polarized light, can be represented by a transformation matrix

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

α is the angle of rotation of the plane of polarization of light under the influence of a magnetic field.

If matrix (9) is substituted into equation (5), then after multiplication of the matrices we find the intensity of the light emerging from the fiber after the second polarizer

In this case, the value of the measured current i can be represented by the expression

It can be seen from equation (11) that with a decrease in the degree of polarization p, the amplitude of the optical signal that carries information about the Faraday effect (about the angle of rotation α) decreases and, accordingly, an error is introduced into the results of measuring the current.

To eliminate this significant drawback, it was proposed in [6, 7] to use a spun fiber as a magnetically sensitive element of the Faraday cell and supply circularly polarized light to the spun fiber instead of linearly polarized light.

Spun fiber is fundamentally different from the rest in that it is obtained by rotating the blank during the drawing process. As a result, this fiber acquires a spiral structure and should be considered as a set of phase plates, the main axes of which rotate when moving in the direction of propagation of light, that is, the quasi-principal directions of optical anisotropy rotate, in which the integral Wertheim's law does not hold.

In this case, when linearly polarized light propagates along a spun fiber, its complete depolarization occurs, and if circularly polarized light is directed instead of linearly polarized light, then its degree of polarization is partially preserved [6]. The degree of conservation of circular polarization depends on the pitch of the spiral structure L _{s of the} spun fiber and the beat length of the built-in birefringence L _in , that is, on the parameter

Such a known device employs a method for measuring the phase difference (1) between right and left circulating polarized light components. The practical implementation of this method [6] is not easy both in terms of manufacturing spun-fiber and creating an infrared interferometer operating at a wavelength of λ = 1550 nm with a special ultrasonic birefringent modulator. The product is complex and expensive.

Known optical AC meter [8], which is a prototype of the proposed device.

This known device contains a light source 1 (Fig. 1), a first light-supplying multimode optical fiber 2, a collimating lens 3 forming a parallel light beam of diameter D, a first linear polarizer 4, a magnetically sensitive element made of optical glass with a high Verdet constant in the form a quadrangular prism 5 with a height h ₁ located in the longitudinal magnetic field of a fragment of a conductor 6 of a high-voltage line, a second polarizer 7, the transmission plane of which makes an angle of ± 45 ° with the transmission plane of the first polarizer 4, a collecting lens 8, a second multimode optical fiber 9, a photodetector 10, and electronic unit 11.

In order to repeatedly pass the polarized light beam of the common path L ₁ , for example, L ₁ = 4h ₁ , the rectangular prism 5 contains one mirror coating 12 in the form of a strip in the middle of the first base of the prism 5 and two mirror coatings on the polished planes 13, 14 of the second base of the prism 5 inclined to the plane of the first base at angles

The known device [8] works as follows.

The light from the source 1 (Fig. 1) is transmitted through the 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 beam of diameter D. Then the light passes through the first polarizer 4, becomes linearly polarized, passes four times the quadrangular prism 5, passes the second polarizer 7 and is collected by the lens 8 at the end of the optical fiber 9. Then the light enters the photodetector 10.

If the current does not flow through the conductor 6 and there is no magnetic field around the conductor 6, then during the passage of light through the prism 5 its polarization state does not change. Since the azimuth of the transmission plane of the polarizer 7 differs from the transmission plane of the polarizer 4 by an angle of ± 45 °, the photodetector 10 perceives light with an intensity

where I ₀ - light intensity of source 1;

R is the total reflection coefficient;

τ is the total transmittance of all elements of the optics.

If the bus 6 flows an alternating current i = i _max sinωt of the mains frequency (ω = 50 Hz), then the photodetector 10 perceives light with an intensity

where: α _max = H _max VL ₁ cos β is the maximum amplitude of the angle of rotation of the plane of polarization of light by the prism 5;

V is the Verde constant of the material of the prism 5;

L ₁ - the total length of the path of light in the prism 5;

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

Photodetector 10 operates in a linear mode, so the luminous flux I is converted into an electrical signal by the photodetector

where U ₀ is the constant component of the electrical signal of the photodetector 10.

In the electronic unit 11, the ratio Q of the variable component is calculated

to the constant component U ₀

and then the sought current i, flowing through the conductor 5, is calculated by the formula

where M is a coefficient characterizing the efficiency of using the magnetic field.

The measurement results of the alternating current are indicated on the digital display of the electronic unit 11 and, using the interface, are transmitted to other external devices.

This known device is superior to other so-called optical current transformers in that optical glass is used as a magnetically sensitive element, and optical fibers are used only to transmit unpolarized light.

However, it has some limitations during operation.

First, according to formulas (17), (18), the amplitude of the increment in the angle of rotation of the plane of polarization α _max should always be less than ± 45 °. So, if at rated current i _{n the} angle of rotation α _max ≈ 5 ° (the preferred mode of operation on the linear section of the curve Q = f (α)), then with an inrush current in the network, for example, as a result of a short circuit (i _kz ≥10i _n ) , angle α _kz > 50 °, which leads to violation of the principle of operation of the device and to the loss of information about the true value of the current.

Secondly, by initially adjusting the optical current meter to the maximum current i _n in real conditions, the measured current can be much less than expected, which leads to a decrease in the measurement accuracy compared to the settings for low currents.

Thirdly, with an increase in the value of the rated current, an increase in the cross-section of the fragment of the conductor (solenoid) is required, i.e. its replacement is required, which is inconvenient during the installation of the optical current meter at the facility.

A new two-channel optical current meter, free from the above-mentioned drawbacks, is proposed.

The two-channel optical current meter contains a precise channel, in which a light source is installed, a first light-supplying multimode optical fiber, a collimating lens, a first polarizer, a magnetically sensitive element in the form of a glass rectangular prism of height h ₁ with mirror coatings to ensure the multiple passage of polarized light of the common path L ₁ located in the longitudinal magnetic field of a fragment of a high-voltage line conductor, a second polarizer, the transmission plane of which makes an angle of ± 45 ° with the transmission plane of the first polarizer, a collecting lens, a second multimode optical fiber, a photodetector, a preamplifier, a signal processing unit, a microprocessor with an indicator of measurement results and interface.

In order to expand the range of current measurements and to ensure the formation of a signal for the operation of relay protection in case of a short circuit, an additional magnetosensitive element of a coarse channel is installed directly near the magnetosensitive element of the precise channel, also in the form of a glass rectangular prism with a height h ₂ <h ₁ , but without mirror coatings. In the second coarse channel, a second light source, a second pair of multimode optical fibers (supplying and receiving light), a second photodetector, and a second electronic unit are installed.

Next, the proposed device is described in detail and illustrated by the drawings.

FIG. 1 shows a block diagram of a known optical AC meter according to RF patent PM No. 171401.

FIG. 2 shows a block diagram of the proposed two-channel optical current meter.

FIG. 3 shows the optical scheme of the precise channel of the proposed two-channel optical current meter.

FIG. 4 shows the optical scheme of the second coarse channel of the proposed device.

FIG. 5 shows a block diagram of the electronic unit.

FIG. 6 shows a fragment of a high-voltage line conductor in the form of one complete turn from a flat copper bus with strips.

FIG. 7 shows the design of the pad.

FIG. 8 shows an embodiment of a fragment of a conductor in the form of two turns connected in series.

FIG. 9 shows the construction of one turn of a two-turn fragment of a conductor with a strap.

The proposed two-channel optical current meter contains an accurate current measurement channel, in which a light source 1 (Fig. 2) is installed in series, a first light-supplying multimode optical fiber 2, a collimating lens 3, a first polarizer 4, a magnetically sensitive element in the form of a rectangular glass prism 5 of height h ₁ , located in the longitudinal magnetic field of the fragment of the conductor 6 of the high-voltage line, the second polarizer 7, the transmission plane of which is ± 45 ° with the transmission plane of the first polarizer 4, the collecting lens 8, the second multimode optical fiber 9, the photodetector 10 and the electronic unit 11.

To ensure multiple, for example, fourfold, passage of polarized light in a rectangular prism 5 (Fig. 2, Fig. 3) of the exact channel, mirror coatings 12, 13, 14. A mirror coating 12 is applied in the form of a strip to the middle of the first base of the prism 5, and mirror coatings 13, 14 are applied to the inclined surfaces of the second base of the prism 5.

Directly next to the magnetically sensitive element (prism) 5 of the precise channel (Fig. 2), an additional magnetically sensitive element 15 of the coarse channel is also installed in the form of a glass rectangular prism 15 (Fig. 4) with a height h ₂ <h ₁ with a light path length L ₂ <L ₁ but no mirror coatings. Polished bases of prism 15 are glued with polarizers 16, 17. Polarizer 16 is protected by a cover plane-parallel plate 18, and polarizer 17 is glued between prism 15 and prism 19 of type BR-180 ° so that its transmission plane coincides with the main section of prism 19. Transmission plane of polarizer 16 makes an angle of ± 45 ° with the transmission plane of the polarizer 17.

In the second coarse channel, a second light source 20 is installed, (Fig. 2, Fig. 4) a second light supplying multimode optical fiber 21, a collimating lens 22, a light collecting lens 23, a second multimode optical fiber 24, which supplies light to the second photodetector 25.

The electronic unit 11 (Fig. 2, Fig. 5) of the proposed device also has two channels. The exact measurement channel contains a photodetector 10 (Fig. 5), a preamplifier 26, a signal processing unit 27 connected to the first input of the microprocessor 28, an indicator of measurement results 29, an interface 30 and a power supply unit 31.

An additional coarse measurement channel contains a photodetector 25, a preamplifier 32, a signal processing unit 33, which is connected to the second input of the microprocessor 28. A trigger-type threshold device 34 with a power amplifier 35 is connected to the preamplifier 32, which is connected to the microprocessor 28 and with a relay protection input (not shown in the drawing).

A fragment of the high-voltage line conductor is made in the form of one or two full turns from a flat copper bus.

(ГОСТ 434-78 и ГОСТ 859-2001) для измерения тока i_н=3000A.By way of example, in FIG. 6 shows an embodiment of a fragment of a conductor in the form of a full turn made of a copper bus ShMM a = 10 mm,

(GOST 434-78 and GOST 859-2001) for measuring current i _n = 3000A.

The inner diameter d of the turn of the fragment of the conductor 6 is selected on the basis of placing prisms 5 and 15 (Fig. 6) in it in the common frame 35 and providing a gap between the frame of the prisms and the fragment of the conductor 6 for air movement to prevent heating of the prisms 5, 15.

(фиг. 6) для подсоединения проводников высоковольтной сети перед формированием полного витка на концах заготовки шины толщиной а=10 мм, шириной

и длиной

выполнены вырезы шириной

и длиной

In order to form conclusions (sites) with a length

(Fig. 6) for connecting the conductors of the high-voltage network before forming a full turn at the ends of the bus blank with a thickness of a = 10 mm, a width

and length

cutouts are made in width

and length

меди фрагмента проводника 6 на его выводах напаяны и проварены по контуру накладки 36 и 37 (фиг. 6, 7),.изготовленные также из медной шины ШММ толщиной а=10 мм и шириной

To maintain the overall section

copper of a fragment of a conductor 6 on its terminals are soldered and welded along the contour of the strips 36 and 37 (Fig. 6, 7), also made of a copper bus ShMM with a thickness of a = 10 mm and a width

(ГОСТ 434-78). Этот вариант конструкции обеспечивает более высокую точность измерений тока в диапазоне до i_н=1200А.FIG. 8, as an example, an embodiment of a fragment of a conductor 6 is shown in the form of two identical turns 38, 39, connected in series by a jumper 40, which are made of a copper bus ShMM with a thickness of a = 8 mm and a width

(GOST 434-78). This design option provides a higher accuracy of current measurements in the range up to i _n = 1200A.

FIG. 9 shows the structure of one turn 38 with a strap 41. The strap 41 is soldered to the turn 38 with solder and additionally welded at the ends by welding.

The inner diameter of two turns 38, 39 (Fig. 8) and the inner diameter of one turn of the fragment of the conductor 6 (Fig. 6) are the same and equal to d. This achieves versatility during installation, depending on the value of the rated measured current i _n = 1200A or i _n = 3000A.

The proposed optical two-channel current meter operates as follows.

The light from the source 1 (Fig. 2) of the precise channel is transmitted through the 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 4, becomes linear polarized, passes four times the quadrangular prism 5, passes the second polarizer 7 and is collected by the lens 8 at the end of the optical fiber 9. Then the light enters the photodetector 10.

If an alternating current of frequency ω (50 Hz) flows through a fragment of a conductor in the form of a full turn of the bus 6

then, according to formulas (2, 15), the photodetector 10 perceives light with an intensity

The luminous flux I _{1 is} converted by the photodetector 10 into an electrical signal

- максимальный угол поворота плоскости поляризации света призмой 5;where:

- the maximum angle of rotation of the plane of polarization of light by the prism 5;

L ₁ is the path traveled by linearly polarized light in prism 5.

и переменную составляющуюAfter pre-amplification by the amplifier 26 (Fig. 5), the signal processing unit 27 separates the DC component of the signal (20)

and variable component

The constant component is supplied to one input of the microprocessor 28, and the variable component is detected, smoothed and fed to the second input of the microprocessor 28.

Microprocessor 28 calculates the ratio Q of the signal proportional to the AC component (21) to the DC component

then calculates the desired current i, flowing through the fragment of the conductor 6 according to the formula (19).

The results of measuring alternating current are indicated on a digital indicator 29 and, using the interface board 30, are transmitted to external devices for registration and control.

At the same time, light with an intensity I ₂ ≈I ₁ from a source 20 (Fig. 2, Fig. 4) of the second coarse channel is transmitted through the multimode fiber 21 to the focal plane of the collimating lens 22. The diverging light beam emerging from the optical fiber 21 is converted by the lens 22 into a collimated light beam also with a diameter D. Next, the light passes the plate 18, the polarizer 16, becomes linearly polarized, passes once the quadrangular additional prism 15, the polarizer 17, is twice reflected from the polished surfaces of the prism 19 of the BR-180 ° type, is collected by the lens 23 (Fig. 4) at the end of the fiber light guide 24 and transmitted to the photodetector 25.

The luminous flux 1 _{2 is} converted by a photodetector 25 into an electrical signal

- максимальный угол поворота плоскости поляризации света призмой 15 (фиг. 2);where:

- the maximum angle of rotation of the plane of polarization of light by the prism 15 (Fig. 2);

L ₂ - the path traveled by linearly polarized light in the prism 15.

After pre-amplification by the amplifier 32 (Fig. 5), the signal processing unit 33 separates the DC component of the signal (23) U ₁ = and the AC component

грубого канала равен или близок к уровню постоянной составляющей точного (основного) канала

А уровень (амплитуда) переменной составляющей грубого канала (23) в несколько раз меньше амплитуды точного канала (21) в связи с тем, что при прочих равных условиях путь L₂, пройденный светом в призме 15 (фиг. 2), в несколько раз (например, в 5 раз) меньше пути L₁, пройденного в призме 5.DC level

of the coarse channel is equal to or close to the level of the constant component of the fine (main) channel

And the level (amplitude) of the variable component of the coarse channel (23) is several times less than the amplitude of the exact channel (21) due to the fact that, other things being equal, the path L ₂ traversed by light in the prism 15 (Fig. 2) is several times (for example, 5 times) less than the path L ₁ traversed in prism 5.

So, for example, if at the rated current in the network i _{n the} angle of rotation of the plane of polarization α _1max in the exact channel is usually in the range from 5 to 10 °, then in the coarse channel it is only 1 ° -2 °.

Therefore, if an inrush current occurs in the network, for example, as a result of a short circuit (i _cc > 10i _n ), then in the exact channel there will be a violation of the principle of operation (α _1max >> 45 °), and in the coarse channel α _2max <45 ° ( α _2max from 5 ° to 10 °) and the optical current meter does not malfunction.

In addition, in the preamplifier 32 of the coarse channel, the variable component signal rises to the level of the trigger-type threshold device 34, which is amplified by the amplifier 35 and supplied to the relay protection to disconnect the network.

информация о измеренном токе i в высоковольтной сети поступает из первого (точного) канала, а с увеличением тока i информация о измеренном токе i поступает из дополнительного (грубого) канала.Microprocessor 28 is programmed so that at an angle α _1max ≤ 30 °, when the ratio of the variable component to the constant component

information about the measured current i in the high-voltage network comes from the first (exact) channel, and with increasing current i information about the measured current i comes from an additional (coarse) channel.

где L₁ - путь, пройденный светом в призме 5 (фиг. 2), a L₂ - путь, пройденный светом в призме 15.So, for example, if a 10 × 100 mm ² bus in the form of one turn is used as a fragment of a high-voltage line conductor (Fig. 6), then at i _n = _3000А α 1max = 9 ° and Q = 0.309, and at a current i ≈ 3i _n ≈ 10000А α _1max ≈ 30 ° and Q ≈ 0.87. That is, when the current in the network is exceeded by more than 3 times, the channels are automatically switched from the first to the second (coarse) and the current measurement continues without loss of information. Of course, this takes into account the coefficient

where L ₁ is the path traversed by the light in the prism 5 (Fig. 2), and L ₂ is the path traversed by the light in the prism 15.

The same happens in the case when an 8 × 60 mm ² bus in the form of two turns is used as a fragment of the conductor (Fig. 8), when i _n = 1200A. So, at i _n = _1200А α 1max = 9 ° and Q = 0.309, and at i _n = 4000А α _1max = 30 ° and Q = 0.87. And in this case, when the current i _{n is} exceeded by approximately three times (i ≈ 3.33⋅1200A ≈ 4000A), automatic channel switching occurs, and the relay protection does not operate yet. The relay protection will operate when the short-circuit current is reached.

Thus, the addition of an additional magnetosensitive element to the known device [8] and the organization of a second additional coarse channel makes it possible to measure current with high accuracy in a wide range of current measurement in a high-voltage network and to ensure guaranteed operation of relay protection only when a short circuit occurs (i _cc > 10i _n ).

SOURCES OF INFORMATION

1. GOST 7746-2001 Current transformers. General technical conditions.

2. Landsberg G.S. Optics: 5th ed., Rev. and add. - M .: Nauka, 1976, p. 618-620.

3. Gojayev N.M. Optics. Textbook for universities. - M .: Mir, 1965, p. 301.

4. Shercliff W. Polarized light. - M .: Mir, 1965.

5. RF patent №2321000, G01R 15/24.

6. Gubin VP, Starostin NI, Przhiyalkovsky Ya.V. Fiber-optic transformers of electric current // Photonics. - 2018. - vol. 12, No. 7 (75).

7. Gubin V.P. et al. Use of spun-type optical fibers in current sensors II quantum electronics. - 2006. - v. 36. No. 3.

8. RF patent (utility model) No. 171401, G01R 15/24.

Claims (2)

1. Two-channel optical current meter, containing an accurate current measurement channel, in which a light source, a first light-supplying multimode optical fiber, a collimating lens, a first polarizer, a magnetically sensitive element in the form of a glass rectangular prism of height h ₁ with mirror coatings are installed in series to ensure fourfold transmission polarized light of the common path L ₁ = 4h ₁ and located in the longitudinal magnetic field of a fragment of a high-voltage line conductor, a second polarizer, the transmission plane of which makes an angle of ± 45 ° with the transmission plane of the first polarizer, a collecting lens, a second multimode optical fiber, a photodetector and an electronic unit, containing a preamplifier, a signal processing unit, a microprocessor with an indicator of measurement results and an interface, characterized in that an additional magnetosensitive element of the coarse channel is installed next to the magnetosensitive element of the precise channel also in the form of a rectangular glass prism, but without mirror coatings, with a height h ₂ <h ₁ with a total light path length L ₂ <L ₁ , on the first base of which the first additional linear polarizer and a cover glass plane-parallel plate are glued, on the second polished base a second an additional linear polarizer and a BR-180 ° prism so that the transmission plane of the second additional polarizer coincides with the main section of the BR-180 ° prism and makes an angle of ± 45 ° with the transmission plane of the additional first polarizer, and a second light source is installed in the second coarse channel, a second multimode optical fiber supplying light to the prism; a second multimode optical fiber supplying light to a photodetector; a second preamplifier; and a second signal processing unit connected to the microprocessor. 2. Two-channel optical current meter according to claim 1, characterized in that in order to regulate the range and accuracy of current measurement, a fragment of the high-voltage line conductor is made in the form of a solenoid of one or two full turns of wide tires with cutouts for forming the leads.

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