RU162955U1 - FIBER-OPTICAL SENSITIVE ELEMENT WITH INTEGRATED TEMPERATURE SENSOR FOR ELECTRIC CURRENT TRANSMITTER - Google Patents

Abstract

A fiber-optic sensor with an integrated temperature sensor for measuring an electric current transducer, comprising a magnetically sensitive optical fiber with an integrated spiral structure of the linear birefringence axes and a radiation reflector at the end, as well as a heat-sensitive optical fiber with a radiation reflector at the end, connected to a polarizing and further with a bending polarizing fiber polarizing fiber optic temperature sensor, which in naturally with a magnetically sensitive optical fiber, they cover the conductor with the measured current, and the turns of the magnetically sensitive optical fiber and the thermosensitive optical fiber of the polarizing fiber-optic temperature sensor are freely laid inside the quartz shell, characterized in that the bending polarizing fiber and the fiber preserving the polarization of the polarizing optical fiber temperature sensor stacked in radius elements belonging to a convex polygon with rounded corners and with numbers scrap of at least three sides.

Description

The utility model relates to temperature-compensated fiber-optic interferometric sensors designed for accurate measurement of electric current or magnetic field and can be used in the electric power industry, in high voltage measurement technology, in the field of relay protection and automation.

Most of the known fiber-optic electric current sensors operate on the Faraday magneto-optical effect, for example, [Fiber-optic current sensor. RF patent RU 2437106]. The sensor consists of optical and electronic modules. The optical module includes a radiation source, a directional coupler, a radiation polarizer, a birefringence modulator, a fiber line and a fiber optic sensitive element having a radiation reflector and a polarization converter (quarter-wave plate) at the ends, and consisting of an integer number of turns of a magnetically sensitive optical fiber with a built-in the spiral structure of the linear birefringence axes wound around an electric current conductor. The electronic module includes a signal processing unit. An electric current in the conductor induces a magnetic field, which, through the Faraday effect, introduces a phase shift between light waves with orthogonal circular polarizations propagating in a magnetically sensitive optical fiber. If a magnetically sensitive optical fiber with a constant sensitivity to magnetic field is wound around a conductor with an electric current in the form of a circuit with an integer number of turns N, then the phase shift between the light waves at the circuit output is determined by the current in the conductor and does not depend on any externally generated magnetic fields, for example, from currents in adjacent conductors. The magnitude of the phase shift is determined

where V is the Verdet constant for the material of the optical fiber, H is the magnetic field strength, dl is the closed loop element l, I is the current in the conductor. The integral is taken along the closed path of the circuit l around the current conductor. In practice, this means an integer number of turns of a magnetically sensitive closed-loop optical fiber of arbitrary shape. The loop is closed by combining a radiation reflector and a quarter-wave plate, which limit the length of the magnetically sensitive fiber. Detection and digital signal processing allow you to measure electric currents (magnetic fields) with a measurement error of 0.2% or less.

A fiber optic sensor element of a magnetically sensitive optical fiber is placed in the body of the sensor head, which protects it from external influences. A conductor with a measured current is placed in the central hole of the sensor head housing. When measuring high-voltage electric current, the sensor head is usually located on high-voltage insulators. A dielectric fiber-optic cable is placed inside the insulator, connecting the fiber-optic sensitive element with the signal processing unit. The distance between the fiber optic sensor and the signal processing unit can reach 1000 m.

A sensor head designed for accurate measurement of operating currents should have temperature compensation for the temperature dependence of the Verdet constant V of the magnetically sensitive optical fiber [A.N. Rose, S.M. Etzel, S.M. Wang. Verdet constant dispersion in annealed optical fiber current sensors, J. Lightwave Technol., 15, pp. 803-807, 1997]. The temperature dependence of the Verdet constant gives an error of (1.0-1.5)% when measuring electric current in the range of operating temperatures from minus 60 ° С to 60 ° С and requires the introduction of a temperature measuring element of a magnetically sensitive optical fiber in order to correction of measurements of electric current.

In the housing of the sensor head, in addition to the main measuring head, additional fiber-optic sensitive elements for measuring current can also be located.

To reduce the effect of temperature on the measured electric current, for example, use [Fiber-optic sensitive element of the measuring current transducer. RF patent RU No. 100630]. The sensitive element is made in the form of turns of an optical fiber covering a conductor with a measured current with a reflecting mirror at the end, which are placed in a tube of insulating material equipped with a device for pumping the dielectric coolant and a device for measuring its temperature. The specified technical solution is able to solve the problem of leveling the temperature field and controlling the temperature of the fiber-optic sensitive element of considerable length. The disadvantage of this technical solution is the complexity and high costs of supplying a coolant for measuring circuits installed on high-voltage insulators.

A device is known [Fiber optic sensing element of a stationary current measuring transducer. RF patent RU 108633]. The fiber-optic sensing element is made in the form of turns of an optical fiber spanning a conductor with a measured current with a reflective mirror at the end, which are placed in a dielectric with high thermal conductivity, are coated with a heat insulator, and are equipped with an electrically safe device for measuring the temperature of the fiber. An optical fiber pyrometer is used as a temperature measuring device. A variant of the device provides for the location of additional temperature measuring devices at different points along the length of the sensing element.

The specified technical solution is able to partially align the temperature field of the magnetically sensitive optical fiber and control the temperature at one or more points. This is especially true for large fiber optic sensors. The disadvantage of the technical solution is the difficulty of its use in small-sized sensor heads mounted on insulators of high-voltage conductors. Placing the thermometer heads of the pyrometers in the sensor head leads to an increase in the dimensions of the latter and to the complication of the sealing unit for the additional optical cable of the pyrometer in the high-voltage insulator. In addition, the used fiber-optic pyrometer has a limitation in the length of the optical cable for communication with the EOB, has a small range in the region of negative temperatures and has a high price.

The closest technical solution is the device [Touch head fiber-optic sensor of electric current. RF patent RU 130718 U1]. The device contains a sealed case, a quartz shell fixed in the groove of the case, sensitive elements made of a magnetically sensitive optical fiber with an integrated helical structure of the axes of linear birefringence and fiber of a fiber-optic temperature sensor, the turns of which are freely laid inside the quartz shell and cover the conductor with the measured current, each sensitive element of the current sensor contains a radiation reflector at one end and a quarter-wave plate at the other end coupled to an optical fiber, polarization-preserving, the radiation reflector and the quarter-wave plate are aligned with each other. The fibers of the fiber-optic temperature sensor and the output end of the fiber, which stores linearly polarized radiation and is part of the optical path of the measuring channel of the temperature sensor, are also placed inside the quartz shell.

The advantage of the technical solution is the location of the magnetically and thermosensitive optical fibers of the current sensor and the temperature sensor inside the quartz shell, which ensures absolute equality of their temperatures. This arrangement suggests that in order to excite the working light waves in the temperature-sensitive fiber of the temperature sensor, linearly polarized radiation is generated to it, generated in the electron-optical block or with the help of a bending polarizing fiber located inside the body of the sensor head. The disadvantage of the technical solution is the need to use, as the transmitting radiation, linearly polarized radiation, as well as the use of expensive optical fiber preserving polarization (Panda type) of considerable length, determined by the distance from the installation site of the electron-optical current transducer block (EOB) to the installation location of the sensor head . The placement of a bending polarizing fiber, requiring a working diameter of its bend of about 100 mm inside the body of the sensor head, significantly increases the dimensions of the latter.

The technical result of the claimed utility model is to reduce the size of the sensor head with a fiber located inside, which preserves the polarization and flexural polarizing fiber of the fiber-optic temperature sensor.

The proposed technical solution used a solid fiber polarizing temperature sensor, a discrete analogue of which is presented in the patent [Optical polarizing temperature sensor. USSR patent SU No. 1547495]. The temperature sensor consists of a fiber broadband radiation source, a 2 × 2 single-mode coupler, a fiber connecting line based on a single-mode coupled optical fiber, a linearly polarized light shaper based on a bending polarizing fiber (bending polarizer), an optical path (8-10) m long based on polarization-preserving optical fiber (Panda type), and a heat-sensitive optical fiber with a radiation reflector (mirror) at the end. As a heat-sensitive optical fiber, a fiber that maintains polarization (Panda type) is used with a length determined by the range of measured temperatures and the length of the polarization beats. The thermosensitive optical fiber is welded with a 45-degree orientation of its birefringence axes to the birefringence axes of the fiber of the optical path, which preserves the radiation polarization. As a result, the supplied linearly polarized radiation excites two orthogonal linearly polarized waves in the heat-sensitive optical fiber. An information signal about the temperature is the phase difference between polarized light waves, determined by the temperature dependence of the birefringence of a thermosensitive optical fiber. After reflection from the reflector of the radiation and interference, the light waves enter the receiving area of the photodetector. The amplitude of the photodetector signal is determined by the phase shift between linearly polarized waves induced in a thermosensitive optical fiber. To eliminate the error due to the power drift of the radiation source, a reference channel is introduced into the optical circuit. A photodetector converts an optical signal into an electrical one. Next, the electrical signal is processed by an electronic circuit that calculates the temperature. A feature of the proposed temperature sensor is the use of a cheap connected single-mode fiber as an optical line for transmitting radiation from an electron-optical block to a sensor head. However, this requires the placement of a linearly polarized radiation former (flexural polarizing fiber) directly in the sensor head of the electric current transducer. Maintaining normal operability of the bending polarizing fiber and, accordingly, the necessary error of the temperature sensor in the operating temperature range of more than 100 ° C is possible with a bending diameter of the polarizing fiber of about 100 mm. Moreover, bending with such a radius is not critical for a fiber preserving polarization. At the same time, the diametrical size of the fiber optic sensing element of the measuring transducer of electric current depends on the size of the cross section of the conductor. So, according to the table. 1.3.31 [Rules for the installation of electrical installations PUE, 7th ed. - M .: Publishing House NTs ENAS, M, 2004] for an admissible continuous current of 1900 A, an aluminum rectangular bus with a section of (120 × 8) mm is required. Taking into account the gaps and walls of the sensor head housing, the diameter of the turns of the magnetically sensitive optical fiber will be at least 200 mm.

The task is to constructively construct a magnetically sensitive optical fiber, as well as a thermosensitive optical fiber, a bending polarizing fiber and a fiber that preserves the polarization of the temperature sensor, having the above diametrical dimensions, in the small size of the sensor head.

The essential features of the claimed utility model are:

- A fiber optic sensor with an integrated temperature sensor for measuring an electric current transducer, comprising a magnetically sensitive optical fiber with a built-in helical structure of linear birefringence axes and a radiation reflector at the end. The sign provides the ability to measure electric current or magnetic field based on the Faraday effect.

- Contains a thermosensitive optical fiber with a radiation reflector at the end, connected to a polarizing fiber and then to a bending polarizing fiber of a polarizing optical fiber temperature sensor. Provides the ability to measure temperature with a polarizing fiber optic sensor.

- Which (a thermosensitive optical fiber with a radiation reflector at the end, connected to a polarizing fiber and then to a bending polarizing fiber of a polarizing optical fiber temperature sensor) together with a magnetically sensitive optical fiber enclose a conductor with a measured current. This arrangement of these optical fibers provides a reduction in the size of the sensor head in the diametrical direction. When the coils of the bending polarizing fiber and the fiber of the polarization-preserving polarizing fiber-optic temperature sensor are located above or below the coils of the magnetically sensitive optical fiber (Fig. 1, Fig. 2), there is no need to place coils of the polarizing fiber of significant diameter (100 mm) in the plane of the sensor head, which would cause an increase in the size of the latter.

- The coils of a magnetosensitive optical fiber and a thermosensitive optical fiber of a polarizing optical fiber temperature sensor are freely laid inside a quartz shell. The close placement of these elements provides the measurement of the actual temperature of the magnetically sensitive fiber of the measuring transducer of electric current in real time, which is necessary to correct the effect of temperature on the accuracy of measuring electric current. The free laying of elements reduces the mechanical and temperature effects of the external environment on the optical fibers and optical fibers on each other due to the rigidity of the quartz shell and the close coefficient of linear expansion of the quartz shell and optical fibers.

A bending polarizing fiber and a fiber retaining the polarization of the polarizing fiber-optic temperature sensor are stacked in radius elements belonging to a convex polygon with rounded corners and with at least three sides. The placement of these optical fibers in the radius elements forming rounding corners of a convex polygon provides bending of a bending polarizing optical fiber with a required radius r while placing it around a conductor with a measured current of large cross section at a diameter larger than the bending radius of the fiber r. In this case, the diametrical overall dimensions of the quartz shell and the arrangement of the radius elements slightly differ from each other (Fig. 1, Fig. 2). It provides the creation of linearly polarized radiation formed on the basis of a bending polarizing fiber placed in radius elements. A fiber that preserves polarization during bending with a radius r retains its properties, therefore, to save space, it is also laid in radius elements. A convex polygon is predominantly regular. However, it may be incorrect, especially with a rectangular cross-section of the current lead (see Fig. 3). The minimum number of sides of the polygon is three, the maximum number of sides is not limited and is determined by the design of the sensor head, it depends on the width of zone 4 (Fig. 1, 2) and the ratio of the sizes of the radius elements and the quartz shell. Radius elements that determine the required bending of a bending polarizing optical fiber can be structurally made as a wall, groove, tube, guide, etc., and are structurally combined.

Salient features that affect the receipt of a technical result are:

- Flexural polarizing fiber and fiber that maintains the polarization of the polarizing fiber optic temperature sensor are stacked in radius elements belonging to a convex polygon with rounded corners and with at least three sides.

The essence of the utility model is illustrated by drawings. In FIG. 1 shows a layout of a quartz shell and radius elements belonging to a regular polygon with three sides and a round busbar of a current lead (a conductor with a measured current). In FIG. 2 shows a layout of a quartz shell and radius elements belonging to an irregular polygon with four sides and a flat busbar. In FIG. 3 shows an embodiment of four radius elements in the form of grooves combined in a guide. In FIG. 4 shows a section AA of the guide shown in FIG. 3. In FIG. 1-4 optical fibers are conventionally not shown. The numbers in FIG. 1-4 are indicated: 1 - a radius element, 2 - a polygon, 3 - a guide, 4 - a zone (between the dashed lines) for the placement of a quartz shell, radius elements, a thermosensitive optical fiber, a bending polarizing fiber, and a fiber that preserves the polarization of a polarized optical fiber temperature sensor 5 - current lead (conductor with measured current), 6 - quartz shell. The letters denote: a - side of the polygon, r - radius of the radius element (radius of rounding of the corners of the polygon).

In the sealed housing of the sensor head, a central hole is made where the current lead 5 is placed. In the case, in zone 4, a quartz shell, a heat-sensitive optical fiber, radius elements, a bending polarizing fiber and a fiber that preserves the polarization of the polarized fiber-optic temperature sensor are placed. Inside the quartz shell 6, loops of a magnetically sensitive optical fiber with a radiation reflector and a quarter-wavelength λ / 4 plate, as well as a heat-sensitive optical fiber of a fiber-optic temperature sensor with a radiation reflector at the end, are freely laid. A bending polarizing optical fiber and a fiber that maintains the polarization of the fiber-optic temperature sensor are stacked in radius elements 1, which provide the required bending radius r of the polarizing fiber. Between the radius elements 1, the polarizing optical fibers lie freely (along the sides a of the polygon). The optical fibers connecting the sensor head and the ELF are placed in a dielectric optical cable, which is mounted at the entrance to the sensor head to prevent it from moving along and around its axis. The tightness of the entry point of the optical cable into the sensor head is ensured by the design of the mating parts.

An example of the utility model is a fiber-optic sensor with a built-in temperature sensor for measuring an electric current transducer, containing three circuits of a magnetically sensitive optical SPUN fiber with a different number of turns and a polarizing fiber-optic temperature sensor with a polarizing and bending polarizing fiber placed in touch head. Radiation reflectors are obtained by cleaving optical fibers and spraying a metal. The quarter-wave plates are made of optical fiber preserving the polarization of radiation. We used a broadband optical radiation source with a working wavelength of λ = 1550 nm. Magnetosensitive optical fibers and a thermosensitive optical fiber of a polarizing fiber-optic temperature sensor are placed in a quartz shell with an average diameter of D = 206 mm. The dimensions of the quartz shell did not exceed 212 mm and were limited by the overall dimensions of the cross section of the conductors. Radius elements are combined into a guide made in the form of a ring of non-magnetic, dielectric material with overall dimensions D = 220 mm / d = 190 mm, thickness 7 mm, with 5 radius elements made in the form of grooves having radii r = 57 mm and with 5 open slots for free placement of fibers. The electric current was measured in the range up to 5000 A. During the measurement, the sensor head was placed in a heat chamber where the temperature of magnetically sensitive optical fibers was varied and controlled in the range from minus 60 ° С to 60 ° С. Data on the actual temperature of magnetically sensitive optical fibers were used to correct the readings of the measured electric current. The measurements of alternating electric current showed a relative error of ± 0.1%.

Claims (1)

A fiber-optic sensor with an integrated temperature sensor for measuring an electric current transducer, comprising a magnetically sensitive optical fiber with an integrated spiral structure of the linear birefringence axes and a radiation reflector at the end, as well as a heat-sensitive optical fiber with a radiation reflector at the end, connected to a polarizing and further with a bending polarizing fiber polarizing fiber optic temperature sensor, which in naturally with a magnetically sensitive optical fiber, they cover the conductor with the measured current, and the turns of the magnetically sensitive optical fiber and the thermosensitive optical fiber of the polarizing fiber-optic temperature sensor are freely laid inside the quartz shell, characterized in that the bending polarizing fiber and the fiber preserving the polarization of the polarizing optical fiber temperature sensor stacked in radius elements belonging to a convex polygon with rounded corners and with numbers scrap of at least three sides.

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