RU2620927C1 - Optical ac measuring device - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: claimed optical AC measuring device based on a Faraday cell for high-voltage power lines comprises of a light source and a multimode optical fiber, a collimator, the first polarizer, an active element of the Faraday cell made of a transparent material, the second polarizer, which transmission plane forms an angle of ±45° with the transmission plane of the first polarizer, all series-installed along the beams. The photodetector is made in the form of a collecting lens, the second multimode optical fiber, a photodetector, a linear amplifier of the photodetector signal, a signal conversion unit. The active element of the Faraday cell is made of glass with a high Verdet constant in the form of a cylinder and is installed inside a solenoid formed by a fragment of the conductor of the high-voltage power line, and one end of the cylinder is perpendicular to its generating line, polished and its surface is coated with a mirror coating. The other end of the cylinder contains the input and output polished surfaces which are inclined, forming an edge between them, which intersects the axis of the cylinder, and forming angles

with the plane of the end of the cylinder, where D is the diameter of the cylinder, and ℓ is the length of the cylinder.

EFFECT: increased accuracy of the value measurement and expanded range of the measured alternating current.

4 cl, 2 dwg

Description

The invention relates to the field of information-measuring systems, current measuring transducers of high-voltage energy and electrophysical installations, and, in particular, to polarization devices for measuring current strength, which use the effect of rotation of the plane of polarization of linearly polarized light by a substance located in a longitudinal magnetic field (effect Faraday).

Traditionally, to measure the alternating current in high voltage power lines, current transformers are used in the form of a coil of copper wire with a large number of turns, which is worn on a fragment of the conductor (bus) of the power line. Due to the alternating current flowing through the conductor fragment, an alternating magnetic field arises around it, which induces an alternating potential difference proportional to the current in the coil.

A significant drawback of traditional current transformers is that its coil, being at zero potential, must be reliably isolated from a fragment of a power line conductor at high potential.

With the growth of the power transmission line class, insulation requirements sharply increase and design requirements become more complicated. This drawback can be eliminated if instead of a traditional current transformer, a Faraday cell is used, which can all be at a high power transmission line potential, and light can be supplied to the cell from the source and received for supplying it to the photodetector using optical fibers, which are dielectrics.

It is known that if it is established in the center of a solenoid of N turns that the substance has a large Verde constant and linearly polarized light is directed at it, and the current i passes through the solenoid, then the effect of rotation of the plane of polarization by an angle can be detected at the output of the substance

where: N is the average value of the longitudinal magnetic field acting on the cylinder;

V is the Verdet constant of the substance;

L is the length of the active substance;

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

N is the number of turns of the solenoid;

I is the current flowing through the conductor of the solenoid;

k is a design coefficient that takes into account the ratio of the length, diameter of the solenoid and averaging of the magnetic field strength at various points of the substance.

Such a device is sometimes called a Faraday cage.

By measuring the angle of rotation of the plane of polarization, it is possible to determine the magnitude of the current i flowing through the conductor of the solenoid of the Faraday cell,

where N, k, V and L are constant values for a particular Faraday cell design.

It should be noted that the dependence of the angle of rotation of the plane of polarization α on the magnetic field strength H and the dependence of the magnetic field H on the current of the solenoid i are linear functions, which simplifies the task of measuring currents, for example, in high-voltage power lines (power lines).

Sometimes, to measure current in high voltage lines, a special optical fiber is used as the active substance of the Faraday cell.

A representative of such well-known devices is the "Current-measuring system using the effect of the Faraday cell" according to US patent No. 3605013, G01R 15/246, 11/16/1968

The block diagram of the device is shown in the patent description.

The known device contains a light source and a multimode optical fiber, a connector, a polarizer, an active element of a Faraday cell, which is a coil of optical single-mode fiber, worn on a fragment of a conductor of a high-voltage line, a second polarizer, the transmission plane of which is ± 45 ° s the transmission plane of the first polarizer, a connector, a multimode optical fiber, a photodetector and an electronic signal conversion unit. During the passage of current i through the conductor around it, a magnetic field appears, the lines of force of which coincide with the turns of an optical single-mode fiber and, therefore, coincide with the direction of propagation of light rays.

A disadvantage of the known device is that during the passage of polarized light through an optical multimode fiber as a result of multiple chaotic total internal reflection at the interface between the core and the fiber sheath, linearly polarized light is converted, and different polarization states are mixed, which leads to partial or complete depolarization of light. Therefore, a multimode optical fiber is unsuitable for use as an active element of a Faraday cell.

Optical fibers called "Panda" or "Bow Tie" are also of little use due to strong birefringence.

In known optical current transformers, a single-mode optical fiber (fiber diameter of 4 μm) is often used as an active element of a Faraday cell, in which the angle of incidence at full internal reflection is close to 90 ° and its polarization state changes less during the propagation of polarized light in it. Such an optical fiber can be represented as a set of phase plates introducing a small phase difference δ, the main axes of which are randomly located with respect to the plane of polarization of the light passing through the fiber. As a result, partial depolarization of light occurs with a depolarization coefficient Δp.

If an alternating current with a frequency of ω = 50 Hz flows through the conductor, then the light intensity I perceived by the photodetector changes according to the law

where I ₀ is the light intensity of the source;

p = 1-Δp is the degree of polarization of light after the optical fiber 5;

Δp is the depolarization coefficient of light in the optical fiber;

α _max - the maximum value of the angle of rotation of the plane of polarization of light corresponding to the maximum amplitude of the magnetic field around the conductor;

ω = 50 Hz is the frequency of the alternating current in the conductor.

The signal conversion unit determines the ratio

and then the desired current i in conductor 4:

It can be seen from the equation that the partial depolarization of light Δp directly affects the angle of rotation of the plane of polarization α and, therefore, the result of measuring the current i.

In addition, the effect of depolarization reduces the dynamic range of measurements.

A device is known for measuring electric current and magnetic field according to US patent No. 4608535 dated 02.12.1982, IPC G01R 33/02.

The device is based on a Faraday cell. The Faraday cage is made of a material consisting of bismuth oxide of silicon (Bi ₁₂ SiO ₂₀ ) or germanium bismuth oxide (Bi ₁₂ GeO ₂₀ ) having a relatively large Verdet constant, having a thickness of 3 mm and containing a reflective layer consisting of multilayer dielectric films formed on both sides.

The surface of the Faraday cup can be coated with a transparent and electrically conductive thin film obtained by sputtering In ₂ O ₃ or In ₂ O ₃ -SnO ₂ to eliminate the effects of external electric fields.

The device allows you to measure electric current and magnetic field with high sensitivity, while placing it in the immediate vicinity of the conductor.

The disadvantage of this device is the low dynamic stability of the optical element (Faraday cages), and therefore the entire device, due to the fragility of this optical element (Faraday cages) - 3 mm thick. The design of the device is fragile and for its use in open high-voltage substations requires substantial refinement to ensure rigidity, strength, protection against precipitation and exposure to temperatures from -35 to + 60 ° C (GOST 12997 (P52931).

The complexity of the design increases the use of the yoke (the yoke is part of the magnetic system of electromechanical converters and transformers, not bearing the main windings and serving to close the magnetic circuit) with a Faraday cell built into it. The yoke in the structure is necessary for the concentration of the magnetic field, i.e. to increase the sensitivity (accuracy) of the device. Without this yoke, the device becomes insensitive at low current and voltage values in the conductor, which reduces the measurement range. An increase in the thickness of the optical element (Faraday cage) will lead to a difference between the thickness of the optical element (Faraday cage) and the thickness of the yoke, which will reduce the concentration of the magnetic field on the rays of polarized light passing through the optical element. Accordingly, this will lead to a decrease in the sensitivity of the device. Which in turn limits its scope. An increase in the thickness of the yoke along with the thickness of the optical element (Faraday cage) will lead to a noticeable weighting of the entire structure, which will also limit its scope.

A closer analogue to the claimed optical current transformer is the magneto-optical measuring transducer of alternating current MPR-ME-5 [Magnetooptical measuring transducer of alternating and pulse current MPR-ME-5,000 of NPP MarsEnergo (devices for electric power industry), www.mars-energo. ru), adopted as a prototype.

According to the structural diagram, the MPR-ME-5 AC converter contains a light source and a multimode optical fiber, a collimator, a first polarizer, an active element of a Faraday cell, made in the form of four glass prisms of the AR-180 ° type, spanning a conductor in a circle with current, a second polarizer, the transmission plane of which is ± 45 ° with the transmission plane of the first polarizer, a receiving device in the form of a collecting lens, a second optical multimode fiber, opriemnika and a signal conversion.

The design features of the converter is that four prisms of the type AP-180 ° are arranged sequentially in the direction of light propagation, made of glass and form a closed loop around the current conductor.

For the convenience of input and output of a collimated beam of light, the ends of the first and last prisms are supplemented by wedges. The first polarizer is glued between the wedge and the first prism, and the second polarizer is glued between the wedge and the last prism. The plane of transmission of the polarizer is an angle of ± 45 ° with the plane of transmission of the polarizer.

The end of the optical fiber is installed in the focal plane of the collimator and the end of the second optical fiber is in the focal plane of the collecting lens.

The signal conversion unit contains a power source, a linear amplifier of the signal of the photodetector and a signal processing circuit.

Known magneto-optical measuring transducer of alternating current MPR-ME-5 operates as follows.

The light from the source is transmitted using the multimode optical fiber to the focal plane of the collimator. Then the light in the form of a diverging beam falls on the lens, after it becomes collimated, the first polarizer passes, becomes linearly polarized and passes through the prisms in series.

If there is no current in the conductor, and all the prisms are free from mechanical loads, are made of one type of glass and their main sections are mutually orthogonal in pairs, then linearly polarized light, undergoing total internal reflection, sequentially passes from one prism to another while maintaining the polarization azimuth corresponding to azimuth of transmission of the first polarizer. The transmission azimuth of the second polarizer differs from the azimuth of the first polarizer by an angle of ± 45 °. Therefore, the light intensity I after the second polarizer is Ι = 0.25Ι ₀ , where I ₀ is the intensity of the light incident on the first polarizer. This entire beam of light is collected by the lens at the end of the multimode optical fiber and transmitted through it to the photodetector.

However, the known magneto-optical measuring transducer of alternating current MPR-ME-5 has a number of significant disadvantages.

Firstly, in this known device, the magnetic field arising around a conductor with current i is not effectively used.

In each of the prisms, the 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 H 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 substantially less. In addition, at the ends of the prisms, the direction of the field lines of the field and the direction of light are significantly different, making up the angle β, on which the effect of rotation of the plane of polarization depends according to the Faraday law

In the areas of the transition of light from one prism to another, the rays move parallel to the conductor, that is, perpendicular to the planes of the rings of magnetic lines of force and do not make any contribution to the Faraday effect. Thus, linearly polarized light travels a long way in the glass, and the efficiency of using the longitudinal magnetic field of the conductor is not high.

Secondly, on the basis of this known device it is difficult to create a universal compact OIPT sensor, for example, for open high-voltage substations.

The known design of the device is fragile and for its use in open high-voltage substations requires significant improvements to ensure rigidity, protection against precipitation and exposure to temperatures from -35 to + 60 ° C (GOST 12997 (P52931).

The objective of the proposed technical solution is to create an optical AC meter (optical AC transformer) based on a Faraday cell for high voltage power lines.

EFFECT: high accuracy of measuring the value and expanding the range of the measured alternating current.

The technical result is achieved by the fact that the optical AC meter based on the Faraday cage for high voltage power lines contains a light source and a multimode optical fiber, a collimator, a first polarizer, an active element of a Faraday cage made of a transparent substance, and a second polarizer the transmission plane of which is an angle of ± 45 ° with the transmission plane of the first polarizer, a photodetector in the form of a collecting lens, the second multimode optical fiber, photodetector, linear signal amplifier of the photodetector, signal conversion unit, while the active element of the Faraday cell is made of glass with a high Verde constant in the form of a cylinder and is installed inside the solenoid formed by a fragment of a conductor of a high-voltage power line, and one end of the cylinder is perpendicular to it forming, polished, and a mirror coating is applied to its surface, the other end of the cylinder contains input and output polished surfaces made by inclining They form an edge between themselves that intersects the axis of the cylinder and make up angles with the plane of the end face of the cylinder

- длина цилиндра.where D is the diameter of the cylinder, and

is the length of the cylinder.

The implementation of the invention.

The block diagram of the inventive optical current meter is shown in FIG. one.

In FIG. 2 shows the active element of a Faraday cup in the form of a glass cylinder.

The inventive optical current meter (optical AC transformer) (Fig. 1) contains a light source 1 in the form of a high-intensity LED and multimode fiber 2 installed along the rays, a collimator in the form of a micro-lens 3, the first film polarizer 4, the active element of the Faraday cell 5 in the form a glass cylinder, a fragment of a power line conductor in the form of a solenoid with current 6, a second film polarizer 7, the transmission plane of which is an angle of ± 45 ° with the transmission plane of the first polarizer 4, collecting lens 8, sec e multimode optical fiber 9 and the photodetector 10.

The photodetector 10 is connected to a linear amplifier, which is located in the signal conversion unit 11.

The optical axis of the collimator 3 (Fig. 1) is perpendicular to the input surface of the cylinder, and the optical axis of the photodetector (collecting lens 8 and the end face of the second optical fiber 9) is perpendicular to the output surface of the cylinder. Both polarizers 4 and 7 are made in the form of polaroid films.

As an embodiment, the first polarizer 4 is glued to the input polished surface of the cylinder 5, and the second polarizer 7 is glued to the output surface of the cylinder 5.

The solenoid 6 (Fig. 1), the active element of the Faraday cup (cylinder) 5 with polarizers 4 and 7, the collimator 3 and the collecting lens 8 are mounted in a single block of the Faraday cup 12, which is mounted on the upper part of the hollow high-voltage insulator 13 and is at high potential in relation to the earth, that is, under voltage power lines.

In the inner cavity of the high-voltage insulator 13, multimode fibers 2 and 9 are laid, at the ends of which there are special tips 14 for fixing the ends of the fibers 2 and 9.

The upper tips 14 are fixed in the block of the Faraday cell 12 so that the end face of the optical fiber 2 is in the focal plane of the collimator 3, and the end face of the optical fiber 9 is in the focal plane of the collecting lens 8. There are holes in the bottom of the hollow high-voltage insulator 13 with mounted seals for output optical fibers 2.9 and connections to the electronic unit 15, which is at zero potential, that is, grounded.

The lower tips 14 of the optical fibers 2.9 are fixed in the block 15 so that the end of the fiber 2 is at the light source 1, and the end of the fiber 9 is at the photodetector 10.

The dimensions and, in particular, the length of the high-voltage insulator 13 depend on the class of high-voltage power lines. Therefore, the length of the optical fibers 2.9 also depends on the class of high-voltage power lines and on the location of the electronic unit 15.

The active element of the Faraday cup is made in the form of a cylinder 5 (Fig. 2) made of glass with a high value of the Verdet constant, for example, of glass grade TF5.

One end of the cylinder 5 is perpendicular to its generatrix, polished and a mirror coating is applied on its surface.

The other end of the cylinder 5 contains two polished surfaces that make up angles with the plane of the end of the cylinder

- длина цилиндра.where D is the diameter of the cylinder, and

is the length of the cylinder.

One surface onto which the collimated linearly polarized light is directed is the input, and the other the output. These two input and output polished surfaces form an edge between themselves that intersects the axis of the cylinder.

(фиг. 2).To enhance the Faraday effect (i.e., to increase the accuracy of measuring electric current), a multiple (even number of times) passage of a light beam through a glass cylinder of diameter D and length

(Fig. 2).

The light transmitted through the cylinder is polarized; therefore, distortions of the polarization state during reflection and refraction should be avoided; incoming and outgoing parallel light beams should not vignette and should not touch the generatrix of the cylinder.

Vignetting is the attenuation of a beam of rays passing at an angle with respect to the optical axis in an optical system.

The diameters (dimensions) of the cross section of the incident and reflected light beams must fit into the input polished surface of the cylinder end, i.e. must be no more than 1 / 2D. In this case, the coordinates of the centers of these beams should be 1 / 4D.

From the construction in FIG. 2 it can be seen that inside the glass cylinder for separation at the output of the incident and reflected light beams, the light beam incident on the mirror must fall at an angle γ, which is calculated from the equation

where from

To ensure the necessary direction of incident light at an angle γ in an ordinary cylindrical rod, it would be necessary to direct light to the input part of the cylinder end face at a larger angle than angle γ, since the refractive index of a glass cylinder (glass) is much higher than the refractive index of air. This is undesirable because a linearly polarized light may change upon refraction.

To avoid these problems, incoming and outgoing light beams must enter and exit perpendicular to the inlet and outlet faces of the cylinder. Thus, the input and output faces of the glass cylinder should be “tilted”, i.e. they should be done at an angle

This also helps to simplify the design of the device because in this case it does not matter what magnitude of the refractive index the glass of which the cylinder is made.

Other versions of the proposed optical current meter (optical AC transformer) are possible.

For example, the inclined plane of the cylinder 5 of the active element of the Faraday cell can be made with a mirror coating.

The implementation of the invention

The operation of the inventive optical current meter (optical AC transformer) can be illustrated by the example of the structural diagram shown in FIG. 1, when a fragment of the power line conductor is made in the form of a solenoid 6, and the active element of the Faraday cell 5 is made in the form of a glass cylinder and is inside (surrounded) of the solenoid 6.

The light from the high-intensity LED 1 is transmitted through the multimode optical fiber 2 to the focal plane of the collimator 3. The diverging light beam emerging from the optical fiber 2 is converted by the collimator 3 into collimated, the first polarizer 4 passes, glued to the input surface of the glass cylinder 5 and becomes linearly polarized.

The optical axis of the collimator (lens 3 and the end of the optical fiber 2) is perpendicular to the input surface of the cylinder 5.

Therefore, a linearly polarized collimated beam of light passes through the glass cylinder 5 and falls on its mirror surface at an angle

- длина цилиндра 5.where D is the diameter of the cylinder 5 and

- cylinder length 5.

Further, light reflected at the same angle γ passes through cylinder 5 a second time, passes a second polarizer 7 glued to the output surface of cylinder 5, and is also transmitted to a photodetector 10 using a lens 8 and optical fiber 9.

As an example, consider the case where the cylinder 5 is made of TF5 glass (n _D = 1,755).

If the current i through the solenoid 6 (Fig. 1) does not pass and there is no magnetic field, and there are no mechanical, thermal effects on the cylinder 5, then the light intensity I perceived by the photodetector 10 is equal to:

If AC flows through solenoid 6

i = i _max sinωt of the mains frequency ω = 50 Hz, then

The inevitable loss of light during the formation of the working beam (aperture, vignetting, absorption, etc.) is taken into account by a constant design coefficient k.

Thus, the photodetector 10 perceives light intensity

and converts it into an electrical signal

which after the amplifier is formed in the form of a constant component U ₌ = U ₀ and a variable component

The signal conditioning unit 11 calculates the ratio

and then the desired current i flowing through the solenoid 6 according to the formula

where N is the number of turns of the solenoid 6;

V and L - Verdet constant and cylinder length 5;

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

The measured value of current i is displayed on a digital display and transmitted to external devices using the RS-232C and RS-485 interface.

The inventive optical meter AC has a number of significant advantages compared with known similar devices.

First, at small angles γ, the mirror surface of the active element of the Faraday cell (cylinder) does not introduce any distortion into linearly polarized light. Therefore, the inventive device has high sensitivity and a large dynamic range.

Secondly, the implementation of the active element in the form of a cylinder and its placement inside the solenoid formed by a fragment of a power transmission line conductor, allows the most efficient use of the magnetic field that occurs around the conductor fragment.

Thirdly, a single, or even an even number of times passage of polarized light in the active element increases the sensitivity of the device and its accuracy in measuring alternating current.

Fourth, the implementation of the active element in the form of a glass cylinder with glued polarizers made it possible to achieve compact design, its versatility, rigidity, protection against external influences, and ease of installation.

Fifth, the proposed device has the prospect of even greater efficiency in using the magnetic field of a fragment of a power transmission line conductor, using well-known techniques for using various magnetic circuits to concentrate magnetic field lines along an active element (along a light beam).

Metrological studies of the optical current meter confirmed the achievement of the above technical result, including for small voltages (from 0.4 kV).

The studies were carried out on a multi-function electrical measuring instrument “Energy Monitor-3.1 KM”.

The inventive device can be used not only in high-voltage power transmission lines, but also in other power plants where it is required to measure large alternating currents regardless of the magnitude of the voltage and frequency.

The claimed invention meets the criterion of "novelty", as from available sources of information not identified technical solutions with the same essential features.

The claimed invention meets the criterion of "inventive step", as it is not obvious to a specialist.

The claimed invention meets the criterion of "industrial applicability", as it can be obtained from known means and known methods.

Claims (6)

1. An optical AC meter based on a Faraday cell for high-voltage power lines, containing a light source and a multimode optical fiber, a collimator, a first polarizer, an active element of a Faraday cell made of a transparent substance, and a second polarizer whose transmission plane is angle ± 45 ° with the transmission plane of the first polarizer, a photodetector in the form of a collecting lens, a second multimode optical fiber, a photodetector, A distinctive photodetector signal amplifier, a signal conversion unit, characterized in that the active element of the Faraday cage is made of glass with a high Verdet constant in the form of a cylinder and installed inside a solenoid formed by a fragment of a conductor of a high-voltage power line, while one end of the cylinder is perpendicular to its generatrix, polished and a mirror coating is applied to its surface, the other end of the cylinder contains input and output polished surfaces made inclined and constituting plane angles for cylinder

where D is the diameter of the cylinder, and

- the length of the cylinder, and forming between themselves an edge that intersects the axis of the cylinder. 2. The optical current meter according to claim 1, characterized in that the inclined planes of the cylinder of the active element of the Faraday cell are made with a mirror coating. 3. The optical current meter according to claim 1, characterized in that the polarizers are made in the form of polaroid films and are fixed on the input and output planes of the cylinder. 4. The optical current meter according to claim 1, characterized in that the optical axis of the collimator is perpendicular to the output surface of the cylinder.

Images