RU2720187C1 - Ac and dc optical laboratory meter - Google Patents

Abstract

FIELD: optics; instrument engineering.

SUBSTANCE: invention relates to optical devices using a Faraday effect for measuring electric current. Disclosed device comprises a light source, a first polariser, a quadrangular glass prism with height h, on its first base an additional prism is fixed and a mirror coating is applied, second prism base comprises two polished surfaces with mirror coatings, which are inclined relative to the first base at equal angles γ=arctg(0.5D/h) and make a rib between themselves at the center. Further, along the beam path there is a second polariser in the form of a Wollaston prism with planes of polarization of rays separated by it at angles of ±45 degrees relative to the transmission plane of the first polariser, lenses, photodetectors and an electronic unit. On the first base there is a mirror coating, which occupies 2/3 of its surface, the line of separation between the clean and mirror surfaces is parallel to the rib of the second base of the quadrangular prism. Additional prism is glued to the clean surface of the first base so that its rib is perpendicular to the quadrangular prism rib, and its polished faces are inclined to its base at angles θ=arcsin{n_λsin[arctg(0.5l/L)]}, where n _λ is refraction index of additional prism glass for wavelength of λ light source; l is the distance between the centers of light entering the prism and emerging from it; L is path length of light beam in both prisms. Solenoid embraces a quadrangular prism along its entire height and is made in the form of a set of separate flat multilayer coils identical to the inner diameter from winding conductors laid in layers on each other and interconnected in parallel. Turns form coils containing one to four multilayer turns and connected to each other in parallel when measuring high currents or in series when measuring low currents.

EFFECT: wider range of measurements.

1 cl, 11 dwg

Description

The invention relates to optical devices that use the Faraday effect to measure electric current. The invention will be used as an exemplary current meter in the laboratories of Gosstandart and electric power enterprises.

An exemplary current meter should be universal in terms of current type, have a large measuring range, high accuracy of current measurement, and is also convenient for use.

The existing electromagnetic standard current transformers ITT-5000-5, TTIP-5000/5 and the verification procedure of traditional AC transformers according to GOST 8.217-2003 are not very suitable for testing electronic (digital) current transformers made according to GOST R IEC 60044-8-2010 “Measuring transformers. Part 8 Electronic current transformers. " The main reason for the difficulties is the differences in the systems for recording measured currents.

Currently, electronic optical current meters [1] have appeared on the market of current meters for high-voltage networks, the principle of operation of which is based on the Faraday effect [2].

The main unit of optical current meters is the so-called Faraday cell, which consists of two linear polarizers, between which a magnetically sensitive isotropic transparent substance is installed, for example, optical glass with a large Verdet constant, placed in the magnetic field of the conductor with the current so that the magnetic field vector coincides with the direction of propagation of linearly polarized light in a given substance. A fragment of the conductor may be in the form of a straight bus or in the form of a solenoid containing from one to several turns.

Under the influence of a longitudinal magnetic field of a conductor fragment with current, a magnetically sensitive substance (glass) acquires the ability to rotate (convert) the plane of polarization of linearly polarized light by an angle

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

V is the Verdet constant of a magnetically sensitive substance (glass);

L is the length of the path traveled by a beam of polarized light in a substance;

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

N is the number of turns of the conductor fragment;

i is the current flowing through the conductor;

k is a design coefficient that takes into account the distance of the magnetically sensitive substance to the conductor, averaging the magnetic field at various points of the magnetically sensitive element.

If we assume that the magnetic field H is constant and the magnetically sensitive substance is isotropic, then according to the effect on linearly polarized light it can be represented by a rotator matrix [3]

where α is the angle of rotation of the plane of polarization in accordance with formula (1).

Usually, in the Faraday cells used in optical current meters, the transmission planes of the polarizers differ by an angle of ± 45 °, then the light intensity I at the output of the Faraday cell can be found from the equation

- вектор Стокса не поляризованного света интенсивностью I₀;Where:

is the Stokes vector of non-polarized light of intensity I ₀ ;

[M _P ] _{45 °} [M _P ] ₀ — tabular matrices for ideal polarizers [3] with transmission planes 0 ° and 45 °, respectively.

After multiplying the transformation matrices (3), we find the first parameter of the Stokes vector, which characterizes the intensity of the light I passing through the Faraday cell,

If an alternating current i = i _max sinωt of the mains frequency ω = 50 Hz flows through a conductor fragment, then

and the light intensity I at the output of the Faraday cell changes according to the law

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

It is seen from equations (6, 7, 8) that the Faraday cells for optical AC meters should be made so that the amplitude of the change in the angle of rotation of the plane of polarization a does not exceed ± 45 °. It is desirable that the angle α satisfy the condition | α | <± 30 °.

Therefore, depending on the magnitude of the measured current i, the following should be correctly selected: the material of the magneto-optical element with respect to the Verde constant V, the path length L of the light beam in the magneto-optical element, the design of the conductor fragment with current (number of turns N of the solenoid), which forms a longitudinal magnetic field.

The design of the conductor with the current must be such that the magnetic field lines coincide with the direction of light and the coefficient k is the largest. For example, if this is a solenoid, then you should strive to ensure that the diameter of the solenoid is the smallest (the current conductor should be closer to the magneto-optical element), and its length should be as large as possible.

Typically, the nominal measured current i can be from 100 A to several kiloamperes. The cross section S of the fragments of the conductors of the current meters must correspond to the current i. So, for copper conductors at i = 300 A there should be S≥120 mm ² , and at i = 5000 A it should be S≥2000 mm ² . This raises two problems. Firstly, if thick tires are used as conductors, then there are restrictions for the minimum bending radii of the tires and it is difficult to manufacture solenoids of small diameters. Secondly, with alternating current in thick tires, Foucault eddy currents occur, which leads to additional heating of the conductor with current and heating of the magneto-optical element.

The magneto-optical element of a Faraday cell must be isotropic even when exposed to temperature when a conductor fragment (solenoid) is heated, so that thermal stresses and birefringence effects do not occur, linearly polarized light is converted to elliptically polarized and, ultimately, to the effect of light depolarization.

To ensure a large range of current measurements in an exemplary current meter, the design of a fragment of a conductor with current should allow it to control the intensity of the magnetic field created by it, for example, by changing the number of turns of the conductor cross section.

Digital optical current meters are known, in which an optical single-mode fiber is used as a magnetically sensitive substance, which is wound in the form of a coil and put on a conductor fragment with current so that the fiber turns coincide with the direction of the magnetic field lines of the conductor [4, 5, 6].

Such devices have a number of significant disadvantages.

The main disadvantage is 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 inevitably arises between mutually orthogonal components of polarized light and linearly polarized light becomes elliptically polarized.

The magnitude of the phase difference δ and the degree of ellipticity depends on the orientation of the plane of polarization of the incident light relative to the plane of the interface of the core of the optical fiber and its cladding, as well as on the angle of refraction for each event of internal reflection inside the optical fiber. In addition, when an optical fiber bends, mechanical loads inevitably arise in it, which lead to the appearance of birefringence and to an additional phase difference. Therefore, an optical fiber is an anisotropic substance. Any fiber can be represented as a set of phase plates with different directions of the main axes, converting linearly polarized light to elliptical.

During the propagation of linearly polarized light in an optical fiber, a chaotic 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, in a single-mode fiber, simultaneously with the effect of rotation of the plane of polarization by an angle α, partial depolarization of light occurs with a depolarization coefficient Δp.

Therefore, the magnetically sensitive element of the Faraday cell, made on the basis 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.

If we substitute matrix (9) into equation (3), then after multiplying the matrices we find the intensity of the light emerging from the optical fiber after the second polarizer

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

From equation (11) it is seen that with decreasing degree of polarization p, the amplitude of the optical signal that carries information about the Faraday effect (rotation angle α) decreases and, accordingly, an error is introduced as a result of measuring the current.

Known magneto-optical measuring transformer of alternating current [7], in which the Faraday cell is made in the form of four glass prisms of the type AR-180 ° glued in series so that they surround the conductor with current in a circle. At the entrance of the first prism and at the output of the fourth prism, linear polarizers are fixed, the transmission planes of which make an angle of ± 45 ° between themselves.

Light from a source located at zero ground potential is directed to a Faraday cell under a high voltage network using a multimode optical fiber and a collimator installed behind it.

The light transmitted through the Faraday cell is sent to the photodetector using a multimode optical fiber as well.

This well-known Faraday cell used in the patent [7] works as follows.

The light from the source is transmitted through the first multimode optical fiber to the focal plane of the collimator. Further, after the collimator, the light passes through the first linear polarizer, becomes linearly polarized, all four AR-180 ° prisms pass sequentially, the second polarizer, which collects the lens and is fed to the photodetector using a second multimode optical fiber.

If an alternating current of frequency ω = 50 Hz passes through a fragment of a conductor, then an alternating magnetic field is created around the conductor, the magnetic lines of force of which in the form of concentric rings penetrate the prisms along which linearly polarized light passes in a straight line parallel to the axial line of each prism. The longitudinal component of these lines of force, which coincides with the direction of light propagation in each of the four prisms, creates the effect of rotation of the plane of polarization of light by an angle

where: α _max = H _max VLcosβ;

H _max - the maximum amplitude of the magnetic field around the conductor;

V is the Verdet constant of glass prisms;

L is the path length of polarized light traveled along magnetic field lines;

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

Due to the fact that the main cross section of the subsequent prism is at an angle of 90 ° to the main cross section of the previous prism, the phase difference δ between the components of polarized light, which occurs when total internal reflection is in the previous prism, is compensated in the subsequent prism (if all the prisms are made of the same glass grade ) Therefore, unlike an optical fiber, during the passage of polarized light through all four prisms, depolarization of light does not occur.

However, this known device [7] has significant drawbacks.

First, in this device [7] the magnetic field arising around the current conductor is not used effectively. So, in each of the four prisms, light propagates in a straight line, making up the trajectory of the quadrangle, and the lines of force around the conductor are in the form of concentric rings. Moreover, the magnetic field strength at the surface of the conductor is greatest, and with increasing radius r of the ring decreases according to the law

Therefore, in the zone of the central part of each prism, the field strength H is greatest, and at the ends of the prisms it is substantially less. Moreover, at the ends of the prisms in the light transition from one prism to another, the light propagates perpendicular to the plane of the rings of magnetic lines of force and makes no contribution to the Faraday effect.

Secondly, if you want to achieve high accuracy in measuring AC current, this device does not have the prospects of significantly increasing the path L of polarized light in prisms and increasing the number of turns of a conductor with current.

Thirdly, this known device cannot measure direct current. In the known optical meter of alternating current in high voltage networks according to the patent of the Russian Federation (utility model) No. 171401, G01R 15/24 [8] a more advanced magneto-optical element in the form of a quadrangular prism is used.

This known device contains a collimated light beam source 1 of diameter D (Fig. 1), the first linear polarizer 2, a quadrangular glass prism 3 of height h, which is installed inside the bracket 4 made of a copper bus, are installed in series in the light beam. The first base 5 of prism 3 is polished and a mirror coating is applied in the form of a rectangular strip 6. The other base of prism 3 contains two polished surfaces with mirror coatings 7, 8, which are inclined relative to the first base 5 at equal angles γ = arctg (0.5D / h) and forms among themselves in the center of the base of the rib 9, parallel to the long side of the mirror strip 6.

The transmission plane of the first polarizer 2 is perpendicular to the edge 9 and parallel to the large face of the prism 3. After the prism 3, a second polarizer 10 is installed along the light beam, the transmission plane of which is an angle of ± 45 ° relative to the transmission plane of the first polarizer 2.

The known device [8] operates as follows. The collimated light beam from source 1 passes through the polarizer 2 and becomes linearly polarized, the polarization azimuth of which ψ is perpendicular to the edge 9 and parallel to the large face of the prism 3. The linearly polarized collimated light beam passes through the glass prism 3 and falls onto the mirror surface 7 at an angle γ, is reflected from it , a second time passes through a prism 3, at an angle of 2γ it falls onto a mirror surface of a strip 6, is reflected from it, a third time passes through a prism 3 and at an angle γ falls onto a mirror surface of 8, after reflection from it the prism 3 passes for the fourth time and the second polarizer 10 passes.

а азимут преимущественной поляризации после отраженияSince in this example the plane of polarization of the light incident on the glass-mirror coating boundary coincides with the plane of incidence, for the modules of complex reflection coefficients for the parallel and perpendicular components of polarized light, we can write

and the azimuth of preferential polarization after reflection

.Thus, the glass-mirror coating interface under the above conditions is an isotropic system with a reflection coefficient

.

If current i does not pass through bus 4 and there is no magnetic field, and mechanical or thermal loads do not act on prism 3, then the light intensity at the output of the Faraday cage

where I ₀ is the intensity of the light incident on the first polarizer 2.

If alternating current i = i _max sinωt of the mains frequency ω = 50 Hz flows through bus 4, then the light intensity at the output of the Faraday cell changes according to the law

and the amplitude of the alternating current can be determined by the formula (8):

From formulas (8) and (17) it can be seen that the well-known Faraday cell used in the known device [8] is more advanced than those in which an optical fiber is used as a magneto-optical element.

However, this known device also has significant drawbacks.

Firstly, the known device is designed to measure only alternating current.

Secondly, the fragment of the conductor 4 with alternating current is made of a wide and thick bus, in which eddy currents and a skin effect occur, the magnetic field is distorted and the heating of the fragment of the conductor increases.

Thirdly, the fragment of the conductor 4 has the shape of a bracket, which does not allow the maximum use of the magnetic field arising around the conductor. It is known, for example, that the magnetic field H in the center of a full turn is 1.36 times greater than in the center of the bracket.

Fourthly, to increase the accuracy of measuring current in the known device, it is difficult to increase the path L traveled by the light beam in a quadrangular glass prism 3 Faraday cells.

Known for a more advanced optical current meter [9], containing a monochromatic collimated light source 1 (Fig. 2, 3) of wavelength λ and diameter D, in which the first polarizer in the form of a Wollaston prism 2, a magneto-optical element 3 of a Faraday cell located in longitudinal magnetic field of solenoid 4 with current. The magneto-optical element of the Faraday cage is made in the form of a quadrangular glass prism 3 of height h, its first base 5 is polished, and in the center of the base 5 it is partially coated with a mirror coating in the form of a strip 6 of width D equal to the diameter of the collimated light beam. The second base of the prism 3 contains two polished surfaces 7, 8 with mirror coatings and inclined relative to the first base 5 at equal angles γ = arctg (0.5D / h), comprising the edge 9 in the center of each other. Next, a second polarizer 10 is installed along the rays , an additional prism 11, lenses 13, 14 (Fig. 3) and photodetectors 15, 16, which are connected to an electronic unit with an indicator of measurement results and an interface. The transmission plane of the polarizer 10 is angles of ± 45 ° with the planes of polarization of the rays emerging from the Wollaston prism 2. The additional prism 11 is made of the same glass as the prism 3, its two polished faces form an edge perpendicular to the plane of beam separation by the Wollaston prism 2, and form the same angles θ with the third polished face of the additional prism 11 that satisfy the condition

where: β is the angle of ray dilution with the Wollaston prism 2;

n is the refractive index of the glass of prisms 3 and 11.

The known optical current meter universal works as follows. A collimated, monochromatic light beam from a source 1 (Fig. 2, 3) falls on the first polarizer 2, made in the form of a Wollaston prism and is divided by it at an angle of 2β into two linearly polarized light beams of equal intensity with mutually orthogonal planes of polarization.

Next, the separated light beams lying in a plane perpendicular to the plane of the drawing (Fig. 2) pass through the magneto-optical element (prism 3), are reflected from the mirror surface 7, pass through the element 3 for the second time, are reflected from the mirror plane 6, the element 3 passes through the third time, are reflected from the mirror surface 8, the element 3 passes for the fourth time, the second polarizer 10 passes, they are refracted in the prism 11 and the lenses 13, 14 (Fig. 3) are directed to the photodetectors 15, 16. If a direct current flows through the solenoid 4, then the photodetectors 15, 16 transform beam ki of light with intensities I ₁ and I ₂ in electrical signals

where α is the angle of rotation of the plane of polarization of light.

In the electronic unit, the ratio is calculated

and the value of the measured direct current

where c = NVLK is a constant value depending on the number of turns N of the solenoid 4, the Verdet constant V of the glass of the prism 3, the length of the light path in the prism 3, and the coefficient of utilization of the magnetic field k.

If an alternating current of the mains frequency ω and a magnetic field inside the solenoid 4 flow through solenoid 4, it is also variable H = H _max sinωt, then the output of photodetectors 15, 16 will be electric signals

The variable components of the signals U ₁ and U _{2 of} frequency ω are in antiphase, therefore

The variable component of the electrical signal is detected, smoothed, so the microprocessor of the electronic unit finds the ratio Q and the magnitude of the measured current according to formulas (21) and (22).

The known device under consideration [9] is universal both in terms of the type of measured current (alternating or direct) and in voltage (only the design of an insulator depends on the high voltage class).

However, this known device [9] also has drawbacks that prevent it from being used as an exemplary laboratory current meter.

The known device does not contain structural features for adjusting the range of measurement of currents while maintaining high sensitivity and accuracy of measurement of currents. So, for example, with a solenoid made of copper conductors with a cross-section S = 240 mm ² , consisting of four turns (N = 4), the permissible rated current i _nom = 240 mm ² ⋅ 2.5 A / mm ² = 600 A and H = i⋅N = 600 ⋅4 = 2400A⋅volka. If a light beam travels in a magneto-optical substance with a path L = 280 mm, then according to the experiment, the nominal angle of rotation of the plane of polarization is α = NiVkL = ± 9.67 °, which, with the sensitivity of measuring the angle of rotation α _min = ± 0.006 °, corresponds to the current sensitivity Δi = ± 0.415A, i.e. 0.18 ° of the measured value.

If it is required to measure large currents, for example, i = 2000A, then the cross section of the solenoid S = 240mm ^{2 is} insufficient (S≥800mm ² is required), and the angle of rotation of the plane of polarization at such a current is α> 32 °, which is outside the permissible range.

And if the nominal measured current is less, for example, i _nom ~ 100A, then with the same design the current sensitivity is Δi = ± 0.373A, which corresponds to an error of current measurements of 0.373% (almost half as much as stipulated by GOST 7746-2001). Therefore, in the model current meter should be a high sensitivity current measurement and adjustment (selection) of the cross section S of the conductor and the number of turns N of the solenoid.

A new ac and dc optical laboratory meter is offered, free of the aforementioned drawbacks.

The optical laboratory AC and DC current meter contains a source of a monochromatic collimated light beam of wavelength λ and diameter D, in which the first polarizer, the magneto-optical element of the Faraday cell, which is located in the longitudinal magnetic field of the solenoid with current, are installed. The magneto-optical element is made in the form of a quadrangular glass prism of height h, its first base is polished, an additional prism of the same glass is fixed on it, and a mirror coating is partially applied. The second base of the quadrangular prism contains two polished surfaces with mirror coatings inclined relative to the first base at equal angles γ = arctan (0.5D / h) and constitute an edge between them in the center. Further along the rays, a second polarizer is installed in the form of a Wollaston prism with polarization planes of the rays separated by it at angles of ± 45 ° relative to the transmission plane of the first polarizer, lenses, photodetectors, and an electronic unit.

In order to increase the path of the polarized light beam in the quadrangular prism and, accordingly, increase the sensitivity and accuracy of current measurements, a mirror coating is applied to 2/3 of its surface on the first base of the quadrangular prism so that the interface between the clean and mirror surfaces is parallel to the edge of the second base quadrangular prism. An additional prism is glued to the clean surface of the first base so that its edge is perpendicular to the edge of the quadrangular prism, and its polished faces are inclined to its base at equal angles

where n _λ is the refractive index of the glass of the additional prism for wavelength λ, radiation of the light source;

l is the distance between the centers of the light beam entering and leaving the prism;

L is the path length of the light beam in a quadrangular and additional prisms.

To achieve consistently high accuracy in measuring currents over a wide range, the solenoid is designed to cover a quadrangular prism over its entire height h and is made up of a set of separate flat, identical in diameter inner multilayer turns of winding conductors, for example, flat buses laid in layers on top of each other friend and interconnected in parallel. Multilayer coils form coils containing one to four multilayer coils. The coils are equipped with standard lugs for connecting them to conductive busbars and to each other in parallel when measuring high rated currents (for example, from 500A to several kiloamperes), sequentially when measuring low rated currents (for example, up to 300A) and for mixed connection (for example, for measuring rated currents from 200 to 600A).

In FIG. 1 shows a structural diagram of a known optical meter of alternating current in high voltage networks according to the patent of the Russian Federation No. 171401.

In FIG. 2 shows a structural diagram of a known optical universal current meter according to the patent of the Russian Federation No. 2682133 (front view, in sections).

In FIG. 3 shows a structural diagram of a known optical universal current meter according to the patent of the Russian Federation No. 2682133 (side view, in sections).

In FIG. 4, 5 shows a structural diagram of the proposed new meter AC and DC optical laboratory.

In FIG. 6 shows the design of one full turn of the solenoid.

In FIG. 7 shows the design of the proposed coil of four turns, consisting of four layers of winding conductors in the form of a rectangular bus.

In FIG. Figure 8 shows the design of one full turn of a solenoid, consisting of two multilayer turns of winding copper conductors in the form of a 2 × 4 mm ² bus connected in parallel using standard tips.

In FIG. 9 shows the construction of a solenoid consisting of five coils (FIG. 7) connected in parallel.

In FIG. 10 shows the construction of a solenoid consisting of five coils (Fig. 7), four multilayer turns of winding conductors in each, connected in series.

In FIG. 11 shows the construction of a solenoid consisting of seven paired turns (FIG. 8) connected in parallel.

The proposed AC and direct current optical laboratory meter contains a source of a monochromatic collimated light beam 1 (Fig. 4, 5) of wavelength λ and diameter D. The first polarizer 2 is installed in the light beam, for example, in the form of a polaroid, a magneto-optical element of a Faraday cell made in in the form of a quadrangular glass prism 3 of height h.

The magneto-optical element 3 is located inside the solenoid 4, that is, in a longitudinal magnetic field and is made in the form of a quadrangular glass prism 3 of height h. The first base 5 of prism 3 is polished, 2/3 of its surface is coated with a mirror coating 6.

The second base of the quadrangular prism 3 contains two polished surfaces 7, 8 (Fig. 5) with mirror coatings that are inclined relative to the first base at equal angles γ = arctg (0.5D / h) and in the center of the base comprise an edge 9.

After the quadrangular prism 3, a second polarizer is installed in the form of a Wollaston prism 10 (Fig. 4) with polarization planes of its separated rays at angles of ± 45 ° relative to the transmission plane of the first polarizer 2.

The line is divided between the mirror coating 6 (Fig. 5) and the clean surface of the first base 5 parallel to the edge 9. An additional prism 11 of the same glass as the prism 3 is glued onto the clean surface of the first base 5, so that its edge 12 (Fig. .4) perpendicular to the edge 9 of the quadrangular prism 3. The polished faces of the additional prism 11 are inclined to its base and, therefore, to the first base 5 of the prism 3 at angles (27)

where n _λ is the refractive index of the glass of the prism 11 for the wavelength of light λ;

l is the distance between the centers of the light entering the prism 11 and the light emerging from it;

L is the path length of the light beam in a quadrangular 3 and an additional 11 prisms.

In the beams separated by the Wollaston prism 10, lenses 13, 14 are installed (Fig. 4), which collect light on photodetectors 15, 16. Photodetectors 15, 16 are connected to the electronic unit 17.

In order to achieve a consistently high accuracy in measuring currents in a wide range of their nominal values, the solenoid 4 covers a quadrangular prism 3 over its entire height h and is made in the form of a set of separate coils of the same inner diameter, containing from one to four multilayer turns of winding conductors (Fig. 6, 7, 8).

So in FIG. 6 shows the design of one full turn of a multilayer 18 containing four segments of a copper bus bar with a section of 2 × 4 mm ² laid in layers on top of each other and connected in parallel.

In FIG. 7 shows the construction of a coil 19 of four multilayer coils consisting of four layers of a conductor in the form of a copper bus bar with a section of 2 × 4 mm ² . At the ends of the coil, tips 20 are soldered for ease of installation in the solenoid.

In FIG. 8 shows the design of a coil of a single turn, containing two multilayer turns 18, interconnected in parallel.

As an example in FIG. 9 shows a General view of one of the options of the proposed solenoid, designed to measure currents up to 600A, in which there are five coils 19 (Fig. 6), interconnected in parallel. To supply current to the coils 19, the tips 20 connected to the beginning of the coils are connected to the copper bus 21 (Fig. 8), and the tips 20 connected to the ends of the coils 19 are connected to the bus 22 (Fig. 9) using screws 23.

Tires 21 and 22 are fixed on the protrusions 24 of the base 25, made of dielectric material. Tires 21, 22 have platforms with threaded holes 26, 27 for connecting to a conductor with a measured current.

In FIG. 10 shows a General view of a variant of the proposed solenoid, designed to measure currents up to 100A, in which there are five coils 19 (Fig. 7), but connected in series. For this, the coils 19 are turned through one (FIG. 10) around the axis by 180 °, and copper bridges 28 are provided in series for connecting them. The bridges 28 have flats 29 and are inserted into the grooves 30 made in the protrusions 24 of the base 25.

In FIG. 11 shows a General view of a variant of the proposed solenoid, designed to measure currents up to 1400A, in which seven paired multi-layer coils 18 (Fig. 8) are installed, connected in parallel.

The proposed meter AC and DC optical laboratory operates as follows.

The light from the source 1 (Fig. 4) passes through the polarizer 2, becomes linearly polarized, the polarization azimuth of which is perpendicular to the edge 9 of the prism 3 (in Fig. 5 is in the plane of the drawing), is refracted in the plane of the main section of the prism 11 and through the first base 5 enters prism 3 with a deviation relative to the initial direction by an angle

- угол наклона входной грани призмы 11 относительно ее основания;Where

- the angle of inclination of the input face of the prism 11 relative to its base;

n _λ is the refractive index of the glass of prisms 3 and 11;

l is the distance between the centers of the light entering the prism 11 and the light emerging from it;

L is the path length of the light beam in the quadrangular prism 3 and the additional prism 11.

A linearly polarized collimated light beam deflected in the plane of the drawing (Fig. 4) passes through the glass prism 3, falls onto the mirror surface 7 (Fig. 5), and is reflected from it with a deviation of an additional angle already in the plane of the main section of the prism 3

where D is the diameter of the light beam;

h is the height of the prism 3.

Next, the light beam passes the second time the glass prism 3, is reflected from the mirror surface 6 in the zone 31, the third time passes the prism 3, is reflected from the mirror surface 8, passes the prism 3 for the fourth time, is reflected from the mirror surface 6 in zone 32, for the fifth time passes prism 3, is reflected from mirror surface 8, passes prism 3 for the sixth time, is reflected from mirror surface 6 in zone 33, passes prism 3 for the seventh time, is reflected from mirror 7, passes prism 3 for the eighth time, and is refracted on the surface of prism 11 ( fi . 4) and falls on the Wollaston prism 10.

Prism 10 distributes a parallel beam of light into two beams lying in the dilution plane, which is an angle of ± 45 ° with respect to the transmission plane of the first polarizer 2. Lenses 13, 14 collect light beams separated by prism 10 and direct them to photodetector 15 and 16, respectively.

The light intensities I ₁ and I ₂ , perceived by the photodetectors 15, 16, are proportional to the first Stokes parameters, which we find after multiplying the transformation matrices of the optical elements according to the equation

вектор Стокса, характеризующий излучение источника света 1;Where:

Stokes vector characterizing the radiation of a light source 1;

- матрица преобразования линейного поляризатора 2;

- transformation matrix of the linear polarizer 2;

- матрица преобразования призмы 3, когда по соленоиду протекает постоянный ток, зеркальные поверхности которой характеризуются общим коэффициентом отражения R;

- prism 3 transformation matrix when a direct current flows through the solenoid, the mirror surfaces of which are characterized by a common reflection coefficient R;

- матрица преобразования призмы Волластона 10, развернутой по отношению к поляризатору 2 на угол ±45°, знак плюс для одного пучка света, а знак минус для другого пучка света.

- the transformation matrix of the Wollaston prism 10, rotated relative to the polarizer 2 by an angle of ± 45 °, the plus sign for one light beam, and the minus sign for another light beam.

After multiplying the matrices of transformation of the elements of optics we find

Photodetectors 15, 16 convert light beams with light intensities I ₁ , I ₂ into electrical signals (19, 20)

U ₁ = U ₀ (1 + sin2α),

U ₂ = U ₀ (1-sin2α).

The electronic unit 17 (Fig. 4) summarizes the signals

subtracts signals

finds their relationship (21)

and the size of the measured current (22)

where c = NVLK is a constant design coefficient depending on the number of turns N of the solenoid 4, the coefficient of use of the magnetic field k, the Verdet constant V of the glass of the prism 3 and the path length L of the light beam in the prism 3.

If an alternating current of frequency co and magnetic field strength inside solenoid 4 flows through solenoid 4, H = H _max sinωt is also variable, then photodetectors 15, 16 will perceive light intensities

Accordingly, at the outputs of the photodetectors 15.16 there will be electrical signals (23), (24)

U ₁ = U ₀ [1 + sin (2α _max sinωt)],

U ₂ = U ₀ [1-sin (2α _max sinωt)].

After detection and smoothing, the electronic unit 17 finds the ratio

From equations (35), (36), (37) it can be seen that the proposed optical current meter is universal in terms of current type, that is, it can measure both alternating and direct current.

The increase in the area of the mirror coating 6 on the first base 5 of the quadrangular prism 3 to 2/3 of its surface and the fixing of the additional prism 11 on the remaining clean surface of the base 5 made it possible to double the number of passes of the polarized light beam in prism 3 compared to the prototype [9], that is managed to double the length of the path of light L, which according to formula (1) increases the angle of rotation of the plane of polarization of light and thereby increases the sensitivity and accuracy of current measurement.

и

компонент линейно поляризованного света равны, а если угол падения не равен 90°, то

и азимут линейной поляризации изменяется на величинуIn addition, the deviation of the polarized light beam from the optical axis of the prism 3 in two mutually perpendicular directions and its multiple reflections in orthogonal planes from the mirror surfaces of the prism 3 allows us to compensate for the additional uncontrolled effects of the transformation of the azimuth of the plane of polarization of light Δα that occur at each reflection. Studies [10] showed that under normal reflection from a mirror surface, the reflection coefficients

and

the components of linearly polarized light are equal, and if the angle of incidence is not equal to 90 °, then

and the azimuth of linear polarization changes by

where α is the angle of rotation of the plane of polarization of light caused by the Faraday effect.

So, for example, the calculations show that with aluminum mirror spraying on TF glass, the relative refractive index of the reflecting surface is a complex quantity [10]

Therefore, with the angle of incidence γ = 2.8 on the surface 7 of prism 3 and with one pass of light, when the Faraday effect gives α _max ≈ 3 °, the linear polarization azimuth additionally changes by

With four times the passage of polarized light, Δα ≈ 0.03 °, which significantly affects the accuracy of measuring the current i. Therefore, in the known device [9], this phenomenon is partially neutralized by introducing a correction depending on the value of the measured ratio Q according to formula (21), which depends on the angle α.

и

изменяются практически на одну и ту же величину и согласно формулы (38) Δα ≈ 0.In the proposed AC and DC optical optical laboratory meter, the additional effect of the transformation of the azimuth of the plane of polarization Δα is compensated due to the fact that, when polarized light is reflected in mutually orthogonal planes, the reflection coefficients

and

change by almost the same value and according to formula (38) Δα ≈ 0.

If the limits of changes in the measured current are known in advance, then the operator selects the appropriate option for a set of separate flat multilayer coils of the same inner diameter (Fig. 6, 7, 8).

пропорционально 4⋅i_ном=4⋅500A=2000A витков. Общее сечение проводников S=2⋅4⋅5⋅5мм²=200мм². При этом плотность тока в проводниках соленоида 4j=500A/200мм²=2,5A/мм², что не превышает нормы для медных открытых проводников.So, for example, if an exemplary current meter is required to verify current meters used in distribution networks, where i _nom ≤500A, the operator selects the option of a set of coils 19 (Fig. 7) assembled as shown in Fig. 9. The measured current with the help of busbars 21 and 22 (Fig. 7) and tips 20 branches and flows along five coils 19, which cover the glass prism 3 over its entire height h. The magnetic field created in this case in the center of the solenoid 4

in proportion to 4⋅i _nom = 4⋅500A = 2000A turns. The total cross section of the conductors is S = 2⋅4⋅5⋅5mm ² = 200mm ² . Moreover, the current density in the conductors of the solenoid is 4j = 500A / 200mm ² = 2.5A / mm ² , which does not exceed the norm for copper open conductors.

вит., а общее сечение проводников S=2⋅4⋅5=40мм². Плотность тока j=100A/40мм²=2,5А/мм², то есть в пределах нормы.If the measured rated current i _{nom is} ≤100A, the operator selects the option of connecting the coils 19 in series, as shown in FIG. 10. For this, even coils are rotated 180 ° around the axis (around prism 3) and all coils are connected to each other sequentially using jumpers 28. In this case, the total number of turns of the solenoid is N = 4⋅5 = 20 and the magnetic field in the center of the solenoid will be

vit., and the total cross section of the conductors S = 2⋅4⋅5 = 40mm ² . The current density j = 100A / 40mm ² = 2.5A / mm ² , that is, within the normal range.

вит., а плотность тока j=1400A/560мм²=2,5А/мм², т.е. в пределах допустимого.If it is required to measure the current i≤1400A, the operator selects the design of the solenoid shown in FIG. 11, which contains seven separate turns (Fig. 8), interconnected in parallel. In this case, the number of turns N = 1, the total section of the solenoid S = 40⋅2⋅7 = 560 mm ² , the field strength in the center of the solenoid 4

vit., and the current density j = 1400A / 560mm ² = 2.5A / mm ² , i.e. within the acceptable range.

Experimental studies showed that during a linearly polarized light beam L = 560 mm in a prism 3 of height h = 70 mm made of TF5 glass and located in the longitudinal magnetic field of the solenoid 4 of FIG. 9 N = 300A⋅4 turn = 1200A vit., The effect of rotation of the plane of polarization of light by α = 6.2 ° occurs, and the current sensitivity Δi _min ≈ 0.24A, which is 0.08% of the measured value. If the solenoid is assembled according to the circuit shown in FIG. 10, and the rated current i _nom = 100A, the current density j = 100 / 40mm ² = 2.5A / mm ² , then N = 2000A / vit. and α ₂ = 10.3 °, a Δi _min ≈ 0.048 A, which is 0.048% of the measured value.

If the solenoid is assembled according to the circuit shown in FIG. 11, and the rated current i _nom = 1400 A / vit., Then the rotation angle α ₃ = 7.23 °, and Δi _nom ≈ 0.968 A, which is 0.07% of the measured value.

Comparing the data obtained with the requirements of GOST 7746-2001 "Current transformers. General technical conditions ”(table 8), we can conclude that the proposed AC and DC optical laboratory meter corresponds to an accuracy class of 0.1 and can be used as a reference (reference) current meter when calibrating digital current meters with an accuracy class of 0.2S used for commercial metering of electricity.

If you do not reconnect the solenoid 4 and work in the current measurement range i _nom = 1400A, then the solenoid 4 should have a cross section S≥1400A / 2.5 A / mm ² = 560 mm ² . With N = 1 and sensitivity Δi = 0.968A, an accuracy class of 0.1 is ensured. And when measuring currents in the range up to ін = 100А with the same sensitivity, the relative measurement error will already correspond to accuracy class 1 instead of accuracy class 0.1, which is unacceptable.

Thus, the proposed design of an AC and DC optical optical laboratory meter allows the selection and switching of coils 18, 19 (Fig. 6, 7, 8) and, when switching from one range to another, to achieve approximately the same level of magnetic field strength, which allows unchanged the design of the optically active element to achieve the greatest accuracy of current measurements in a wide range of measurements. This is the convenience of design and ease of maintenance. If it is necessary to measure currents of several kiloamperes, it is possible to increase the number of layers in turns 18 and switch to another assortment of copper conductors, but while maintaining the main advantages:

- coil 18 (Fig. 6) should be multi-layer, but flat;

- the coil 19 (Fig. 7) should preferably have from two to six multilayer turns;

- conductors must be copper.

The proposed AC and DC optical laboratory meters will be used in the laboratories of metrological centers involved in the verification of both traditional electromagnetic current transformers and new digital current meters that use the Faraday optical effect.

The relevance of the proposed device is that in the transition to digital technologies in the energy sector, including digital current meters, new verification methods and new equipment are required, that is, new high-precision reference current meters that are similar in manufacturing technology and in principle of operation.

SOURCES OF INFORMATION

1. Gurtovtsev A.L. Optical transformers and current converters // Electrical Engineering News. - 2009. - No. 6.

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

3. Sherkliff U. Polarized light. - M.: Mir, 1965.

4. RF patent No. 2438138, G01R 15/24.

5. RF patent №2321000, G01R 15/24.

6. German patent No. 19547021, G01R 15/24.

7. RF patent (utility model) No. 123965, G01R 15/24.

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

9. RF patent No. 2682133, G01R 15/246.

10. Penkovsky A.I. "WMD", 1986, No. 5. with. 9.

Claims (6)

1. AC and DC optical laboratory measuring instrument, containing a source of a monochromatic collimated long-wavelength light beam λ and diameter D, in which the first polarizer is installed, the magneto-optical element of the Faraday cell located in the longitudinal magnetic field of the solenoid with current, is made in the form of a quadrangular prism of height h , its first base is polished, an additional prism of the same glass is fixed on it and a mirror coating is partially applied, the second base of the quadrangular prism is soda it has two polished surfaces with mirror coatings, inclined relative to the first base at equal angles γ = arctan (0.5D / h), which are in the center of the rib, then along the rays a second polarizer is installed in the form of a Wollaston prism with polarization planes separated by rays at angles of ± 45 degrees relative to the transmission plane of the first polarizer, lenses, photodetectors and an electronic unit, characterized in that in order to increase the path of the polarized light beam in a quadrangular prism and higher In order to measure the accuracy of current measurement, the mirror coating on its first base is applied to 2/3 of its surface, the interface between the clean and mirror surfaces is parallel to the edge of the second base of the quadrangular prism, the additional prism is glued to the clean surface of the first base so that its edge is perpendicular to the edge of the quadrangular prism, and its polished edges are inclined to its base at angles θ = arcsin {n _λ sin [arctan (0.5l / L)]}, where n _λ is the refractive index of the glass of the additional prism for the wavelength λ of the light source; l is the distance between the centers of the light entering the prism and leaving it; L is the path length of the light beam in a quadrangular and additional prisms. 2. The ac and dc laboratory measuring instrument according to claim 1, characterized in that in order to achieve a stably high accuracy in measuring currents in a wide range of their values, the solenoid covers a quadrangular prism over its entire height h and is made in the form of a set of separate planes of the same internal diameter multilayer coils from winding conductors, for example flat busbars stacked in layers and connected in parallel, the coils form coils containing from one to four multilayer coils, which Some are equipped with standard tips for connecting them to conductive busbars and to each other in parallel when measuring high currents or in series when measuring low currents.

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