RU108633U1 - FIBER OPTICAL SENSITIVE ELEMENT OF STATIONARY PERFORMANCE CURRENT TRANSMITTER - Google Patents

Abstract

 1. Fiber-optic sensing element of a stationary current measuring transducer, made in the form of at least one coil of optical fiber enclosing a current with a measured current with a reflective mirror at the end, characterized in that the optical fiber is placed in a dielectric with high thermal conductivity, coated with a heat insulator and equipped with an electrically safe device for measuring its temperature. ! 2. The fiber optic sensing element of the current sensor according to claim 1, characterized in that two or more temperature measuring sensors are used located at different points along the length of the sensing element. ! 3. The fiber optic sensing element of the current sensor according to claim 1 or 2, characterized in that an optical fiber pyrometer is used as a temperature measuring device.

Description

The utility model relates to the field of electrical measurements and can be used in the electric power industry, in high voltage measurement technology, in the field of relay protection and automation.

Traditionally, measurements of electrical quantities in switchgears of industrial enterprises, including power plants, are carried out using electromagnetic current transformers, the cost of which is a significant fraction of the cost of the entire switchgear. A fundamentally different promising approach based on the use of the magneto-optical Faraday effect is implemented in fiber-optic current transformers used in combination with modern digital signal processing and data transmission technologies.

A fiber-optic sensing element is known in the form of a temperature-stabilized sensor coil for a current sensor (see RF patent No. 2358268, IPC G01R 1/00, priority 02.09.2004), containing heat-treated and disposed of in a capillary with antifriction agent, freed from its protective sheath magneto-optical sensor fiber.

A significant drawback of this device is the limited length of the magneto-optical sensing element made of optical fiber and, as a result, the impossibility of accurate measurement of currents in conductors of large cross section, as well as the complexity of its installation in the conditions of the current production.

The closest in technical essence to the claimed is the fiber-optic sensitive element of the measuring current transducer (see Gubin V.P., Isaev V.A., Morshnev S.K. et al. Use of Spun fiber optic fibers in current sensors - Quantum Electronics , 2006, vol. 36, No. 3, p. 287-291.), Made in the form of at least one coil of optical fiber enclosing a conductor with a measured current with a reflecting mirror at the end.

A significant drawback of this device is the low accuracy and stability of measurements in real-life conditions, in particular when installing a fiber-optic sensitive element on current conductors (terminals), the temperature of which changes noticeably during operation and can exceed 60 ° C (up to 120 ° C). When using this device, the measuring signal changes relatively relatively with temperature (usually about a percent by 100 ° C), which unacceptably reduces the accuracy of measurements.

Although the relative change in the Verdet constant of the quartz fiber from the temperature is small and is ~ 10 ^-4 / ^o K, but with a significant range of operating temperatures (for example, about 50 ° K), the relative change in the Verde constant and, accordingly, the measuring signal will be ~ 0.5% , which is already unacceptable during measurements. The presence of induced linear birefringence in an optical fiber caused by the influence of external factors (bends, thermal stresses) in the optical fiber also significantly affects the measurement accuracy. When using swirling optical fiber to reduce the effect of birefringence, the problem of ensuring temperature stability during measurements remains, since torsion-induced circular birefringence in quartz fiber is also quite temperature sensitive.

We were the first to note that a noticeable distortion of the measurement results when using an extended fiber-optic sensitive element is caused not so much by the temperature change of the optical fiber as such during the measurement, but by a change in the temperature gradient along the length of the optical fiber. If the influence of temperature changes can be taken into account, for example, by measuring the ambient temperature, then a change in the temperature gradient can lead to an uncontrolled variation in the error in measuring the electric current in the range from fractions to units of percent.

It was shown that in order to reduce the measurement error in this case, it is necessary to equalize and stabilize the linear temperature of the fiber-optic sensitive element along its entire length.

We have proposed a fiber-optic sensitive element of a measuring current transducer, which allows high-precision, stability, and electrically safe measurements to be taken under actual operating conditions with a significant and non-uniform temperature change in the zone of its location.

We have achieved such a technical effect when in a fiber-optic sensitive element of a current transducer made in the form of at least one coil of optical fiber enclosing a conductor with a measured current with a reflecting mirror at the end. The optical fiber is placed on a coil of insulating material, covered with a dielectric layer with high thermal conductivity and equipped with a device for measuring its temperature. Outside, the structure is covered with a dielectric heat insulator and heat-reflecting material. Approaches to stabilize the linear temperature of the fiber are known.

Depending on the required class of measurement accuracy, a single-mode optical fiber is chosen either with a small internal birefringence or with strong internal birefringence, mainly circular. Optical fiber design approaches are known.

The optical fiber can be made with a protective polymer coating or used without it.

Figure 1 shows the fiber optic sensing element of the current transducer in the form of a single turn of the optical fiber, where the optical fiber 1 with a reflecting mirror 2 at the end, a conductor 3 with a measured current, a dielectric with high thermal conductivity 4, a temperature measuring device 5, a dielectric heat insulator 6, heat-reflecting material 7;

In a similar way, a fiber optic sensing element of a current transducer can be made in the form of an arbitrary number of turns of an optical fiber, at the end of which a reflecting mirror is mounted.

Figure 2 presents a diagram of a measuring current transducer based on an all-fiber low coherent linear Sagnac interferometer with the claimed fiber-optic sensitive element. The diagram shows a light source 9, a directional coupler 10, a photodetector 11, a polarizer 12, a birefringence modulator 13, a fiber line 14, a quarter-wave plate 15, a phase detector 16, a reference oscillator 17, an analog-to-digital converter 18 (ADC) and a computer 19, and also a turn of optical fiber 1 with a reflecting mirror 2 at the end, a conductor 3 with a measured current, a dielectric with high thermal conductivity 4, a temperature measuring device 5, a dielectric heat insulator 6, heat-reflecting material 7.

The proposed fiber-optic sensitive element can be used in measuring current transducers and in another configuration. For example, in a fiber-optic measuring current transducer of a polarimetric configuration [1], as well as in a fiber-optic measuring current transducer of a polarimetric configuration with a Faraday cell [2].

The operation of the fiber optic sensing element will be described in figure 1. The measured electric current I creates a magnetic field around the conductor 3. When linearly polarized light passes through the turn of the optical fiber 1 located in this magnetic field in the forward and, after reflection from the mirror 2, in the opposite direction, the plane of polarization of the light wave rotates through an angle α, connected by the relation

where V is the Verdet constant of the material;

H ₁ - component of the magnetic field along the direction l of light propagation;

dl - closed loop element l.

The angle of rotation of the plane of polarization of the light wave is proportionally dependent on the Verdet constant of the material of the optical fiber. Therefore, a relative change in the Verdet constant for a wide range of operating temperatures leads to a proportional change in the angle of rotation of the plane of polarization of the light wave and, as a result, to a noticeable increase in the measurement error. In addition, the accuracy of measurements is significantly affected by the presence of induced linear birefringence in the optical fiber caused by external factors (bending, thermal stresses), which leads to a change in the polarization state of the light wave - the transformation of linear polarization of light into elliptical. As a result, a shift of the “operating point” occurs and the sensitivity of the measuring current transducer becomes unstable, highly dependent on the temperature conditions of the measurement.

Applying our technical solution, we will align the temperature of the optical fiber along its entire length, reduce the thermomechanical stresses in the fiber, and achieve better temperature stability of measurements. Moreover, to increase the accuracy of measurements, the residual temperature dependence can be corrected when measuring the temperature of the fiber, by introducing a correction factor when processing the measuring signal. Approaches to solving this problem are known.

Consider the scheme in figure 2, the principle of operation of the fiber-optic measuring current transducer. The optical radiation from the light source 9 passes sequentially through the directional coupler 10, the fiber polarizer 12 and enters the input of the birefringent fiber modulator 13 excited by the reference generator 17. Since the transmission axis of the polarizer 12 is oriented at an angle of 45 ° to the birefringence axes of the fiber of the modulator 13, then the radiation propagates through a non-polarizing fiber delay connecting line 14 in the form of two orthogonal linearly polarized light waves (modes x and y) with equal intensities. After passing through a quarter-wave plate 15 made of an optical fiber segment, whose axes are oriented at an angle of 45 ° to the axis of the connecting line 14, two orthogonal linearly polarized light waves are converted into modes with left and right circular polarization. Circularly polarized light waves propagate along the optical fiber 1 of the fiber-optic sensing element in the forward direction a, reflected from the mirror 2, in the opposite direction, and, as a result of the magnetic field around the conductor 3 with current, accumulate a nonreciprocal phase shift φ _F proportional to the measured current I

φ _F = 4VNI,

where V - Verdet constant SPUN - fibers;

N is the number of turns of fiber around the conductor with the measured current.

When reflected from mirror 2, the circular polarization changes to the oppositely directed one, and when the quarter-wave plate 15 passes backward, the circularly polarized modes are again converted to linear ones, the x mode becoming the γ mode and vice versa. As a result, ideally, all phase shifts, except for φ _F , should be compensated and the intensity of the light incident on the photodetector 11 will depend only on the phase shift φ _F.

The voltage from the phase detector 16, configured to select a signal proportional to the frequency of the reference oscillator 17, is digitized by the ADC 18 and recorded by the computer 19.

Any deviation from purely circular polarization associated with a temperature-dependent residual birefringence in a fiber-optic sensitive element leads to a decrease in the magneto-optical sensitivity of the interferometer and an increase in measurement error. By stabilizing with the help of devices 4, 6 and 7 the temperature of the optical fiber 1 of the magneto-optical sensing element along its entire length and introducing a correction temperature coefficient when processing the measuring signal in computer 19, we exclude the temperature sensitivity of the current measuring transducer from temperature.

Concrete example

An experimental sample of the inventive device for measuring alternating electric current was made, in which SPUN fiber was chosen as a magneto-optical sensitive element. The output end of the fiber ended with a perpendicular cleavage acting as a Fresnel mirror. A source of optical radiation was a fiber emitter with a working wavelength of λ = 1550 nm. The birefringence modulator was made of a PANDA type fiber waveguide wound around a 30 mm diameter piezocylinder; the modulator excitation frequency was 40 kHz. A fiber connecting line up to 900 m in length and a phase plate were also made of PANDA optical fiber, preserving the states of radiation polarization.

The intensity of the light signal was measured by a photodiode, digitized using an ADC board, processed on a computer, and displayed on a virtual recorder.

Using an experimental sample, AC electric current was measured in the range from 300 to 30000 A with four turns of SPUN fiber around conductors with a measured current. During the measurements, the temperature of the SPUN fiber changed from + 5C to + 65 ° C, while a change in the measurement error of ~ 0.5% / 30 ° C was observed, which corresponds to the accuracy class of the current sensor 1.0.

When using an experimental sample of the claimed device. Temperature SPUN - The fibers were electrically safe measured with an optical fiber thermometer. The thermometer data was used to correct the readings of the current transducer. In this case, when the temperature in the zone of the fiber-optic sensitive element is changed from + 5 ° С to + 65 ° С, the measurement error did not exceed ± 0.1%, i.e. the temperature dependence of the output signal was practically not observed.

The measurements showed the possibility of determining the value of the measured alternating electric current with a relative error of no worse than ± 0.1%.

Thus, the proposed fiber-optic sensitive element of the measuring current transducer can improve the accuracy and stability of measurements in real operating conditions with a significant change in the linear temperature of the optical fiber during the measurement process. The device is electrically safe, has high noise immunity and, in terms of its accuracy and functional characteristics, can be widely used in the field of electrical measurements, in particular in high voltage measuring equipment.

Literature

1. M.Willsch, P Menke, T Bosselmann Magneto-Optic Current Transformers for Applications in Power Industry - SIEMENS AG Corporate Research and Development ZFE T EP 5, POB 3220, D-91050 Erlangen.

2. Fabien Briffod, Lue Thevenaz, Pierre-Alain Nicati end al. Polarimetric Current Sensor Using an In-Line Faradey Rotator - IEICE Trans. Electron., Vol. EA3-C, no. 3, March 2000, pp. 313-335.

Claims (3)

1. Fiber-optic sensing element of a stationary current measuring transducer, made in the form of at least one coil of optical fiber enclosing a current with a measured current with a reflective mirror at the end, characterized in that the optical fiber is placed in a dielectric with high thermal conductivity, coated with a heat insulator and equipped with an electrically safe device for measuring its temperature. 2. The fiber optic sensing element of the current sensor according to claim 1, characterized in that two or more temperature measuring sensors are used located at different points along the length of the sensing element. 3. The fiber optic sensing element of the current sensor according to claim 1 or 2, characterized in that an optical fiber pyrometer is used as a temperature measuring device.