Optical fiber Fabry-Perot cavity current sensor based on Rogowski coil and method thereof

Abstract

The optical fiber Fabry-Perot cavity current sensor based on the Rogowski coil comprises the Rogowski coil, an OPGW optical cable is sleeved with the Rogowski coil, the Rogowski coil is electrically connected with a giant magnetostrictive rod, one end of the giant magnetostrictive rod is provided with an optical fiber Fabry-Perot cavity, and an optical fiber connected with a demodulator is arranged in the optical fiber Fabry-Perot cavity in a penetrating mode; current on the OPGW optical cable is converted into induced voltage through the Rogowski coil, the induced voltage acts on the giant magnetostrictive rod, the giant magnetostrictive rod generates strain, the optical fiber Fabry-Perot cavity is stretched or compressed, wavelength corresponding to generated interference fringes drifts by changing the cavity length, and current monitoring of the OPGW optical cable is achieved by monitoring the wavelength drift distance. The Rogowski coil can be used for measuring large pulse current, lightning stroke current and short-circuit current, and has the advantages of large dynamic current measurement range and wide frequency band.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical variation monitoring, and in particular relates to an optical fiber Fabry-Perot cavity current sensor based on a Rogowski coil and a method thereof. Background Art

[0002] With the rapid construction of "smart grid", the optical fiber composite overhead ground wire OPGW, which has the dual functions of ground wire and optical cable, is widely used in the field of power communication. Timely collection of OPGW optical cable operating status parameters is crucial to ensure the safe and stable operation of OPGW. The traditional electromagnetic current sensor is based on electromagnetic induction and consists of a ring iron core and windings. It is relatively large in size, and when the current reaches or exceeds the magnetic saturation level of the iron core, its output signal will no longer be proportional to the input current, resulting in measurement errors. It also has a series of problems such as inability to digitize, and cannot provide better performance and convenience. In order to solve the above problems, people introduced optical fiber into the current measurement of OPGW optical cable. AFOC facilitates the operation monitoring of the entire OPGW system and pushes the entire system towards intelligence.

[0003] Fiber optic current sensor technology is an advanced technology that uses optical fiber to transmit optical signals for current measurement. It is based on the change in the refractive index of the optical fiber or the magnetic field effect of the current, and indirectly obtains current information by measuring the change in the optical signal in the optical fiber. Compared with traditional electromagnetic current sensors, fiber optic current sensors have the following advantages: the optical fiber itself is very small, which can achieve a more miniaturized sensor design; the measurement accuracy is high, and it has a wider linear range; it has communication functions and can realize intelligent monitoring. However, the scope of application of fiber optic current sensors is limited. They are usually suitable for smaller current ranges and may not be suitable for high current or high power applications. Even in the measurement of direct current (DC) current, fiber optic current sensors may require additional current conversion circuits, which are not suitable for application in power systems with higher voltage levels.

[0004] The closest prior art solution of the present invention is: A piezoelectric driven fiber Bragg grating current sensor based on a Rogowski coil belongs to the field of optoelectronic measurement technology. The Rogowski coil of the present invention is hung on a high-voltage conductor, and the positive pole and negative pole of the output conductor of the Rogowski coil are respectively connected to the positive and negative terminals of the upper and lower stacked piezoelectric ceramics. The stacked piezoelectric ceramics are composed of a number of piezoelectric ceramic sheets physically connected in series. The right end of the stacked piezoelectric ceramics is fixedly set in a rectangular tube, and the fiber Bragg grating penetrates the central through hole at the right end of the rectangular tube and enters the rectangular tube and is fixedly set at the left end of the stacked piezoelectric ceramics. The external optical fiber is connected to a demodulator. The high-voltage side of the present invention does not require power supply, and the packaging structure makes the bonding of the fiber Bragg grating unnecessary for external stress and protects and sensitizes the sensor element. It has a small size, a simple structure, no magnetic saturation, and is resistant to electromagnetic interference. It has excellent transient tracking capabilities and can respond to current changes at the ms level.

[0005] (2) The second prior art solution closest to the present invention: A fiber Bragg grating voltage sensor based on a Rogowski coil belongs to the field of optoelectronic measurement technology. The fiber Bragg grating is connected to an external optical fiber, and the fiber Bragg grating is bonded to a piezoelectric ceramic through bonding points and bonding points. The fiber Bragg grating and the piezoelectric ceramic remain parallel. The Rogowski coil is connected to the upper and lower ends of the piezoelectric ceramic through the output signal positive electrode and the output signal negative electrode. The Rogowski coil is sleeved on the wire, and the wire is connected to the A-phase bus and the ground-phase bus through the resistor and capacitor to form a loop; the Rogowski coil does not contain an iron core, has no magnetic saturation, and has no hysteresis effect; the fiber Bragg grating is an electrical insulating material with strong anti-electromagnetic interference (EMI) capability; it has excellent transient tracking capability and can respond to voltage changes up to level, and at the same time, it has a simple structure and accurate measurement.

[0006] Both of the above solutions use fiber Bragg grating as the core component of the sensor, but fiber Bragg grating has some disadvantages, including: sensitivity is affected by temperature; the optical fiber in the fiber Bragg grating is very fragile and easily damaged by external physical or chemical factors, such as bending, pressure, stretching, chemical solutions, etc., which may cause the grating performance to degrade or fail, requiring replacement of the optical fiber or repair. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide an optical fiber Fabry-Perot cavity current sensor and a method thereof based on a Rogowski coil in view of the deficiencies in the above-mentioned prior art, which is used to solve the technical problems such as magnetic saturation, small measurement dynamic range, narrow frequency band, etc. encountered when using giant magnetostrictive materials and optical fiber gratings to measure large currents, and has the advantages of high sensitivity and large dynamic range.

[0008] The present invention adopts the following technical solutions: An optical fiber Fabry-Perot cavity current sensor based on a Rogowski coil comprises a Rogowski coil, which is sleeved on an OPGW optical cable and electrically connected to a giant magnetostrictive rod, one end of the giant magnetostrictive rod is provided with an optical fiber Fabry-Perot cavity, and an optical fiber connected to a demodulator is passed through the optical fiber Fabry-Perot cavity; The current on the OPGW optical cable is converted into an induced voltage through the Rogowski coil and acts on the giant magnetostrictive rod, causing the giant magnetostrictive rod to produce strain, stretching or compressing the optical fiber Fabry-Perot cavity, and by changing the cavity length, the wavelength corresponding to the generated interference fringes drifts. The current monitoring of the OPGW optical cable is achieved by monitoring the wavelength drift.

[0009] Preferably, the positive and negative poles of the output wire of the Rogowski coil are correspondingly connected to the positive and negative ports of the driving coil, the driving coil is wound on the giant magnetostrictive rod, and the giant magnetostrictive rod is stacked on the optical fiber Fabry-Perot cavity.

[0010] Preferably, the magnetic field strength generated in the middle of the Rogowski coil is for:

[0011] in, is the axial length of the solenoid coil; is the total number of turns of the solenoid coil; is the transformation efficiency; It is the current to be measured of OPGW optical cable.

[0012] Preferably, the strain generated by the giant magnetostrictive rod is transmitted to the FP cavity of the optical fiber, causing the FP cavity length to change, and the wavelength change monitored by the demodulator is used to obtain the corresponding change in the optical fiber Fabry-Perot cavity length, and finally the relationship between the magnitude of the current to be measured in the OPGW optical cable and the wavelength change is obtained.

[0013] Preferably, the FP cavity of the optical fiber is fixed on the giant magnetostrictive rod in the longitudinal direction as a sensing head.

[0014] Preferably, the change in cavity length when the optical fiber is axially strained is for:

[0015] in, is the sensor length, is the original length of the Fabry-Perot cavity, is the length after axial strain, is the strain coefficient.

[0016] Preferably, the relationship between the magnetostrictive strain of the giant magnetostrictive rod along the axial direction and the external magnetic field is:

[0017] in, is the expansion coefficient of the magnetostrictive material, is the gauge factor, is the original length of the Fabry-Perot cavity, is the change in cavity length, is the magnetic field strength generated in the middle of the Rogowski coil.

[0018] Preferably, the wavelength variation detected by the demodulator is The relationship between the change in the length of the corresponding fiber Fabry-Perot cavity is:

[0019] in, is the initial length of the Fabry-Perot cavity, is the change in the length of the Fabry-Perot cavity, is the wavelength of incident light.

[0020] Preferably, the OPGW optical cable current to be measured is The size and wavelength change The relationship between them is:

[0021] in, is the transformation efficiency; is the axial length of the solenoid coil; is the total number of turns of the solenoid coil; is the sensor length; is the expansion coefficient of the magnetostrictive material.

[0022] Preferably, the giant magnetostrictive rod and the optical fiber Fabry-Perot cavity are fixed inside the housing.

[0023] Another technical solution of the present invention is a method for using a fiber optic Fabry-Perot cavity current sensor based on a Rogowski coil, comprising the following steps: The Rogowski coil is mounted on the OPGW optical cable and electrically connected to the giant magnetostrictive rod; one end of the giant magnetostrictive rod is connected to the optical fiber Fabry-Perot cavity, and the optical fiber is ensured to be arranged in the optical fiber Fabry-Perot cavity, and the optical fiber demodulator at the other end is connected to the monitoring equipment; When current flows through the OPGW optical cable, the Rogowski coil converts the current into an induced voltage, which acts on the giant magnetostrictive rod. The induced voltage causes the giant magnetostrictive rod to produce strain, thereby stretching or compressing the optical fiber Fabry-Perot cavity to produce interference fringes, and the corresponding wavelength drifts. Real-time monitoring of the OPGW optical cable current is achieved by monitoring the wavelength drift, and current data is determined by the obtained wavelength drift; the operating status of the power system is determined based on the monitored current data.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: The invention discloses an optical fiber Fabry-Perot cavity current sensor based on Rogowski coil, which adopts the structure of Rogowski coil + Fabry-Perot cavity. When a fault occurs in the power system, the core of the traditional current transformer will be severely saturated, thereby causing the secondary current to be distorted, and then leading to the false operation of the relay protection. Their manufacturing process is very complicated, the electrical insulation performance is poor, the accuracy is easily affected by the quality of components, and the electromagnetic interference is serious. The optical fiber sensor has some advantages that the traditional sensor does not have. The optical fiber Fabry-Perot cavity has extremely high sensitivity and accuracy that is not easily affected by components, high safety performance, anti-electromagnetic interference, good electrical insulation performance, corrosion and high temperature resistance, wide frequency band, and integrates sensing, transmission, and demodulation. It is compatible with digital communication systems, and has small size, light weight, slenderness and softness, easy layout, and is suitable for accurate monitoring of harsh electromagnetic environments.

[0025] Furthermore, with the increase of voltage level, when there is a large impact current, pulse current or lightning current, the traditional current sensor will have problems such as electromagnetic saturation. When the current sensor is electromagnetically saturated, the signal on the secondary side will be distorted and will cause the relay device to malfunction. The high-voltage current sensor is large in size, which increases the difficulty of installation and transportation, and oil leakage and other phenomena will also occur. The driving coil of this device is wound on the giant magnetostrictive rod. It is a hollow coil. When the measured current passes through the center of the coil, a voltage signal is obtained in the secondary coil due to electromagnetic induction. This sensor can achieve an accuracy of 0.1%. Since there is no iron core, there is no magnetic saturation problem and the measurement range is not limited. The Rogowski coil has no iron core, wide bandwidth, less distortion, large dynamic measurement range, no saturation, and has a good linear relationship with the primary current.

[0026] Furthermore, during the movement of the giant magnetostrictive rod, the length of the Fabry-Perot cavity can be changed by squeezing the cavity body, so that the wavelength of the receiver-monitored signal changes; the change in current is measured by monitoring the change in the wavelength of the signal through the receiver. Compared with the fiber grating measurement method, this structure is more stable, less susceptible to environmental influences, and has a longer service life.

[0027] In summary, the present invention can measure large pulse current, lightning current and short-circuit current by using the Rogowski coil, and has the advantages of large dynamic range and wide frequency band for measuring current.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings to be used in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 It is a schematic diagram of the structure of the present invention.

[0031] Among them: 1. Rogowski coil; 2. OPGW optical cable; 3. Optical fiber; 4. Optical fiber Fabry-Perot cavity; 5. Giant magnetostrictive rod; 6. Driving coil. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, in the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0036] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0037] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0038] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0039] The combination of Rogowski Coil and Fabry-Perot Cavity is usually used for current measurement and related physical quantity monitoring, where the Rogowski Coil is responsible for measuring the magnetic field changes generated by the current, while the Fabry-Perot Cavity may convert the current changes into optical signals for measurement through some mechanism (such as mechanical coupling). However, in the standard combination, the Fabry-Perot Cavity is not directly connected to the Rogowski Coil to measure the current, but may indirectly reflect the current by measuring other physical quantities (such as displacement, strain, etc.) caused by the current.

[0040] The present invention provides an optical fiber Fabry-Perot cavity current sensor based on a Rogowski coil. The current on an OPGW optical cable is converted into a lower voltage through the Rogowski coil. The induced voltage acts on a magnetostrictor to cause the magnetostrictor to generate strain. As the magnetostrictor is deformed, the Fabry-Perot cavity is stretched or compressed to change its cavity length. The wavelength corresponding to the interference fringes generated therefrom drifts. The OPGW optical cable current monitoring is achieved by monitoring the wavelength drift.

[0041] See also Figure 1The present invention discloses an optical fiber Fabry-Perot cavity current sensor based on a Rogowski coil, comprising a Rogowski coil, a magnetostrictor and a Fabry-Perot cavity; the Rogowski coil 1 is sleeved on an OPGW optical cable 2, the positive and negative poles of the output wire of the Rogowski coil 1 are correspondingly connected to the positive and negative pole ports of a driving coil 6, the driving coil 6 is wound on a giant magnetostrictive rod 5, the giant magnetostrictive rod 5 is stacked on an optical fiber Fabry-Perot cavity 4, the giant magnetostrictive rod 5 and the optical fiber Fabry-Perot cavity 4 are fixed inside a shell, an optical fiber 3 passes through the optical fiber Fabry-Perot cavity 4 and is connected to a demodulator at a receiving end; the optical fiber 3 is fixed on the giant magnetostrictive rod 5 in the longitudinal direction as a sensing head, the strain generated by the giant magnetostrictive rod 5 is transmitted to the optical fiber 3, so that the FP cavity length of the optical fiber 3 changes, the wavelength change amount monitored by the demodulator is used to obtain the corresponding optical fiber Fabry-Perot cavity length change amount, and finally the relationship between the magnitude of the measured current and the wavelength change amount is obtained.

[0042] As a highly sensitive current sensor, Rogowski coil 1 is cleverly mounted on the optical fiber composite overhead ground wire (OPGW cable 2). OPGW cable 2 not only carries communication signals, but also takes into account the grounding and lightning protection functions in the power transmission line. The integration of Rogowski coil 1 further enhances its current monitoring capabilities. Rogowski coil 1 uses the principle of electromagnetic induction to non-contactly measure the current changes flowing through OPGW cable 2 and convert it into a voltage signal proportional to the current. This design ensures the accuracy and real-time performance of current monitoring, which is of great significance for the status monitoring, fault diagnosis and protection control of the power system.

[0043] The output wire of the Rogowski coil 1 is accurately connected to the positive and negative terminals of the driving coil 6 through a carefully designed connection method. As a key component of the conversion device, the driving coil 6 is responsible for amplifying the weak voltage signal output by the Rogowski coil 1 and converting it into sufficient magnetic field energy to drive subsequent physical processes. This design realizes efficient conversion from electrical signals to magnetic signals, providing the necessary driving force for the subsequent giant magnetostrictive effect.

[0044] As a high-performance smart material, the giant magnetostrictive rod 5 is firmly fixed inside the device. It uses the magnetostrictive effect, that is, under the action of an external magnetic field, the length of the material will undergo a small but measurable change. Here, the giant magnetostrictive rod 5 is stacked on the optical fiber Fabry-Perot cavity 4, and the two are closely combined to form a precise sensing unit; when the magnetic field generated by the driving coil 6 acts on the giant magnetostrictive rod 5, the slight change in its length will be accurately transmitted to the optical fiber Fabry-Perot cavity 4, resulting in a corresponding change in the cavity length of the optical fiber Fabry-Perot cavity 4, thereby modulating the optical signal transmitted in the optical fiber 3.

[0045] As the transmission medium of the entire system, the optical fiber 3 runs through the entire device. It is not only responsible for converting the current information from the Rogowski coil 1 into an optical signal for long-distance transmission, but also carries the optical signal modulated by the optical fiber Fabry-Perot cavity 4. At the receiving end, these optical signals are sent to the demodulator for decoding and processing, restoring the original current information and the tiny displacement information caused by the giant magnetostrictive effect. This process realizes the complete conversion and transmission from electrical signals to optical signals and then to electrical signals, ensuring the accuracy and speed of information.

[0046] The FP cavity (Fabry-Pérot cavity) of the optical fiber 3 is an optical resonant cavity, which is composed of two mirrors, which are located at the two ends of the optical fiber 3. This cavity is used to enhance the optical signal or to generate a stable light wave; the principle of the FP cavity is similar to that of the cavity in the laser, and the optical signal is reflected back and forth inside the cavity through the reflection of the mirror, thereby achieving light amplification or stabilization.

[0047] In fiber-optic communications, FP cavities are used to generate stable light waves, which are very important for certain types of fiber-optic sensors and fiber-optic lasers. For example, a fiber Bragg grating (FBG) is a common fiber-optic FP cavity, which reflects light of a specific wavelength and allows light of other wavelengths to pass through by forming a periodic grating structure in the optical fiber. This characteristic makes FBG widely used in fiber-optic communications, fiber-optic sensors, and fiber-optic lasers.

[0048] In summary, the whole system builds a high-sensitivity and high-precision current and displacement monitoring platform through the coordinated work of Rogowski coil 1, driving coil 6, giant magnetostrictive rod 5, fiber Fabry-Perot cavity 4, optical fiber 3 and demodulator. By using fiber Fabry-Perot cavity and demodulator, extremely accurate measurement of displacement change is carried out, which helps to improve the measurement accuracy of the whole system. By using OPGW optical cable, monitoring of equipment that is far away or difficult to directly access can be achieved, which is very useful for maintenance and fault diagnosis. The system is not only suitable for current monitoring of OPGW optical cable, but can also be expanded to other industrial and scientific research fields that require accurate measurement of current and displacement changes.

[0049] The working principle of the optical fiber Fabry-Perot cavity current sensor based on Rogowski coil of the present invention is as follows: The Rogowski coil 1 is a circular solenoid coil with a certain number of turns formed by evenly winding a thin wire on a circular frame, which is used to convert the current on the OPGW optical cable 2 into an output voltage. The current-voltage-electromagnetic conversion is realized by connecting the driving coil 6. The driving coil 6 generates an AC driving magnetic field and a bias magnetic field. The giant magnetostrictive rod 5 expands and contracts in the longitudinal direction under the action of the driving coil 6. The optical fiber 3 is fixed on the giant magnetostrictive rod 5 in the longitudinal direction as a sensing head. The strain generated by the giant magnetostrictive rod 5 is transmitted to the FP cavity of the optical fiber 3, so that the FP cavity length changes. The wavelength change monitored by the demodulator is used to obtain the corresponding change in the fiber Fabry-Perot cavity length, and finally the relationship between the magnitude of the measured current and the wavelength change is obtained.

[0050] When the giant magnetostrictive rod 5 is affected by the magnetic field generated by the driving coil 6, it undergoes longitudinal expansion and contraction; this expansion and contraction is adjusted by the control input to achieve precise position control. In this example, the expansion and contraction of the giant magnetostrictive rod causes a tiny strain in the optical fiber on it, and this strain is transmitted to the FP cavity of the optical fiber. The FP cavity (Fabry-Pérot cavity) is an optical resonant cavity, and the change in its length causes the change in the reflected wavelength; this wavelength change is monitored and analyzed by a demodulator, and a relationship based on the wavelength change to represent the actual current size is established, and the actual current value is calculated based on the measured wavelength change; this process not only improves the accuracy and real-time performance of the measurement, but also reduces the demand for high-impedance sensors in the power system.

[0051] The magnetic field strength generated in the middle of the coil for: (1) in, is the axial length of the solenoid coil; is the total number of turns of the solenoid coil; is the transformation efficiency; It is the current to be measured of OPGW optical cable.

[0052] The relationship between the magnetostrictive strain of the magnetostrictive material rod along the axial direction and the external magnetic field is: (2) in, is the expansion coefficient of the magnetostrictive material, is the gauge factor, is the original length of the Fabry-Perot cavity, is the change in cavity length, is the magnetic field strength generated in the middle of the Rogowski coil.

[0053] The change of cavity length when the fiber Fabry-Perot sensor experiences axial strain for: (3) in, is the sensor length, is the original length of the Fabry-Perot cavity, is the length after axial strain, is the strain coefficient.

[0054] The wavelength change detected by the demodulator The relationship between the change in the length of the corresponding fiber Fabry-Perot cavity is: (4) in, is the initial length of the Fabry-Perot cavity, is the change in the length of the Fabry-Perot cavity, is the wavelength of incident light.

[0055] OPGW optical cable current to be tested The size and wavelength change The relationship between them is: (5) in, is the transformation efficiency; is the axial length of the solenoid coil; is the total number of turns of the solenoid coil; is the sensor length; is the expansion coefficient of the magnetostrictive material.

[0056] A method for using a fiber optic Fabry-Perot cavity current sensor based on a Rogowski coil comprises the following steps: S1. Put the Rogowski coil on the OPGW optical cable and electrically connect it to the giant magnetostrictive rod; connect one end of the giant magnetostrictive rod to the optical fiber Fabry-Perot cavity, and ensure that the optical fiber runs through the optical fiber Fabry-Perot cavity, and connect the optical fiber demodulator at the other end to the monitoring equipment; S2. When current passes through the OPGW optical cable, the Rogowski coil converts the current into an induced voltage and acts on the giant magnetostrictive rod. The induced voltage causes the giant magnetostrictive rod to produce strain, thereby stretching or compressing the optical fiber Fabry-Perot cavity to produce interference fringes, and the corresponding wavelength drifts. S3. Real-time monitoring of the OPGW optical cable current is achieved by monitoring the wavelength drift, and current data is determined by the obtained wavelength drift; and the operation status of the power system is determined based on the monitored current data.

[0057] S301, calibration: After the sensor is installed, it needs to be calibrated. That is, under the condition of known current, the data of corresponding wavelength drift is recorded. By comparing the actual wavelength drift with the wavelength drift under known current, the relationship between wavelength drift and current can be established; S302, generate a reference curve: using the calibration data, a reference curve can be generated. This curve reflects the corresponding relationship between the wavelength drift and the current; S303, real-time monitoring: In actual applications, by monitoring the wavelength drift, the corresponding current value can be found on the reference curve. This current value is the actual current size on the OPGW optical cable; S304, data processing: In order to improve the measurement accuracy, the wavelength drift can be subjected to certain mathematical processing (such as filtering, amplification, etc.) to reduce the measurement error. At the same time, multiple sensors can be used for distributed measurement to improve the accuracy and reliability of the overall measurement; S305. Output result: Based on the obtained current data, the data can be transmitted to a monitoring device or other related equipment through an output interface (such as RS-232, RS-485, etc.) for further data analysis and processing.

[0058] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0059] The structure composed of Rogowski coil and fiber Fabry-Perot cavity (FP cavity) has high application potential in sensing technology, but specific products that directly combine these two technologies may not be common because their principles and application fields are different. However, the possible working principle and application scenarios of this combined structure can be explored theoretically.

[0060] Rogowski Coil, also known as Rogowski Coil, is a hollow annular coil used to measure AC current in a conductor. Its working principle is based on the law of electromagnetic induction, that is, the AC current flowing through the conductor will generate an alternating magnetic field around the conductor, thereby inducing an AC voltage signal in the coil that is proportional to the rate of change of the current. Rogowski coil has the advantages of no ferromagnetic material, no eddy current loss, and small phase difference, and is widely used in the accurate measurement of current in power systems.

[0061] Fiber Fabry-Perot Cavity is a fiber optic sensor based on the principle of light interference. It creates a Fabry-Perot cavity inside the optical fiber. When a coherent light beam is incident into the Fabry-Perot cavity along the optical fiber, the light beam is reflected at the two end faces of the cavity and then returns along the original path and meets to produce interference. Changes in external parameters (such as temperature, pressure, stress, etc.) will cause changes in the cavity length, which in turn causes changes in the interference signal. By detecting changes in the interference signal, changes in external parameters can be deduced. Fiber Fabry-Perot cavity sensors have the advantages of simple structure, high measurement accuracy, and large measurement range, and are widely used in the measurement of various physical quantities.

[0062] Although Rogowski coils and fiber Fabry-Perot cavities are different in principle, their combination may be used in some special sensing applications. For example, Rogowski coils can be used to measure the AC current in a conductor and convert the current signal into a voltage signal. Then, using the high-precision measurement capability of the fiber Fabry-Perot cavity sensor, the voltage signal is used as an external parameter input of the fiber Fabry-Perot cavity, and the change in current is accurately measured by detecting the change in the interference signal.

[0063] However, this combination structure may face some challenges in practical applications. For example, how to ensure that the voltage signal output by the Rogowski coil can be stably input into the fiber Fabry-Perot cavity sensor and avoid interference and attenuation during signal transmission; how to design a suitable signal processing system to accurately extract and analyze useful information from the interference signal, etc.

[0064] This combined structure may be used in complex environments where current and other physical quantities need to be measured simultaneously. For example, in power systems, it can simultaneously monitor parameters such as current and temperature of transmission lines; in the field of industrial automation, it can be used to measure motor current while monitoring its vibration and stress state.

[0065] The fiber Fabry-Perot current sensor based on Rogowski coil is an innovative sensor that combines the high sensitivity of Rogowski coil and the high-precision measurement technology of fiber Fabry-Perot cavity. This sensor has broad application prospects in the fields of power, industrial automation, scientific research, etc. The following is an expanded use example that shows the application of this sensor in different scenarios.

[0066] In the power system, current monitoring of high-voltage transmission lines is crucial to ensure the safe and stable operation of the power grid. Traditional current sensors may suffer from poor measurement accuracy or damage due to factors such as harsh environment and electromagnetic interference. The fiber-optic Fabry-Perot cavity current sensor based on Rogowski coil is an ideal choice for solving this problem due to its high sensitivity, anti-electromagnetic interference and resistance to harsh environment. The specific implementation steps are as follows: 1. Sensor installation: The fiber optic Fabry-Perot cavity current sensor based on Rogowski coil is installed at key nodes of high-voltage transmission lines, such as substation incoming and outgoing lines, large current branch points, etc.

[0067] Ensure that the sensor is at an appropriate distance from the transmission line to avoid damage due to direct contact and to optimize measurement accuracy.

[0068] 2. System integration: Connect the sensor to a central monitoring station or data acquisition system via optical fiber.

[0069] Configure system parameters, including sampling frequency, data transmission protocol, etc., to ensure the real-time and accuracy of data.

[0070] 3. Real-time monitoring: The high-precision measurement technology of the optical fiber Fabry-Perot cavity is used to monitor the current changes in the transmission line in real time.

[0071] The non-contact measurement principle of the Rogowski coil avoids direct interference with the transmission line and improves the stability and reliability of the measurement.

[0072] 4. Data analysis and early warning: The collected current data is analyzed in real time to identify abnormal current fluctuations or overload conditions.

[0073] Set the warning threshold. When the current exceeds the safe range, the system automatically sends a warning signal to notify the operation and maintenance personnel to handle it.

[0074] 5. Remote control and optimization: Combined with smart grid technology, remote control and optimized scheduling of transmission lines can be achieved.

[0075] According to the real-time current data, the grid operation parameters are adjusted to improve the energy efficiency and stability of the grid.

[0076] 6. Effect: Improve measurement accuracy: The fiber-optic Fabry-Perot cavity current sensor based on the Rogowski coil can accurately measure current changes in high-voltage transmission lines and improve measurement accuracy and reliability.

[0077] Enhanced system stability: Real-time monitoring and early warning functions help to promptly detect and address potential problems in the power grid, enhancing the stability and security of the power grid.

[0078] Optimize resource allocation: Realize reasonable allocation and efficient utilization of power grid resources through remote control and optimized scheduling.

[0079] Simulation experiment: In order to verify the performance of the optical fiber Fabry-Perot cavity current sensor based on the Rogowski coil of the present invention, corresponding simulation experiments are carried out, as follows: S1. Establish mathematical model; The mathematical models of Rogowski coil, giant magnetostrictive rod and fiber Fabry-Perot cavity are established; the interaction relationship between the components is determined based on the principles of electromagnetism and material mechanics.

[0080] Electromagnetic characteristics of Rogowski coil: The induced electromotive force of the Rogowski coil is proportional to the current passing through it and can be described by Faraday's law of electromagnetic induction: in, is the induced electromotive force, is the magnetic flux, It's time.

[0081] In order to more accurately describe the electromagnetic characteristics of the Rogowski coil, the finite element method or magnetic circuit analysis method is used to establish its mathematical model.

[0082] The induced electromotive force of Rogowski coil e ( t ) and the current passing through the coil i ( t ) is proportional to the time derivative and can be expressed as:

[0083] in, M is the mutual inductance of the Rogowski coil, which depends on the coil geometry, the number of turns, and the relative position of the coil to the conductor.

[0084] Mechanical properties of giant magnetostrictive rods: The strain of a giant magnetostrictive rod is proportional to the applied magnetic field strength and can be described by the magnetostrictive effect:

[0085] in, e It's strain. l is the magnetostriction coefficient, H is the magnetic field strength.

[0086] In order to describe the mechanical properties of giant magnetostrictive rod more accurately, the mathematical model is established by using the principle of material mechanics and finite element method.

[0087] The elongation of the giant magnetostrictive rod Δ l The magnetic field strength H Proportional, expressed as:

[0088] in, is the saturation magnetostriction coefficient of the material, which describes the maximum elongation of the material under a saturation magnetic field.

[0089] Dynamic Model: In practical applications, the response of the giant magnetostrictive rod may be affected by the internal damping and inertia of the material, so its dynamic behavior can be described by a second-order linear system:

[0090] in, m is the equivalent mass, c is the damping coefficient, k is the elastic coefficient.

[0091] Optical properties of fiber Fabry-Perot cavity: The cavity length of the fiber Fabry-Perot cavity is proportional to the applied strain and can be described by the optical resonant cavity theory:

[0092] in, L is the cavity length, is the initial cavity length, is the strain sensitivity coefficient of the optical fiber, It's strain.

[0093] In order to describe the optical properties of the fiber Fabry-Perot cavity more accurately, we can use the optical resonant cavity theory and the finite element method to establish its mathematical model.

[0094] The interference spectrum of the fiber Fabry-Perot cavity is determined by the phase difference between the reflected light and the transmitted light. ϕ Cavity length L and the refractive index of light propagating in the cavity n related:

[0095] in, l is the wavelength of the incident light.

[0096] When cavity length L When a change occurs (e.g. due to strain or temperature change), the interference pattern will move accordingly, and the change in cavity length can be inferred by measuring the amount of movement of the interference pattern.

[0097] S2. Select appropriate simulation software; Select appropriate simulation software according to actual conditions, such as ANSYS, COMSOL Multiphysics, etc.

[0098] S3, setting simulation parameters; Set the number of turns, diameter, wire diameter and other parameters of the Rogowski coil.

[0099] Number of turns: N =100 turns diameter: D =100mm (average diameter of the coil, i.e. the diameter of the circle surrounding the conductor) Wire diameter: dwire =0.5mm Height (coil axial length): h =20mm These parameters will affect the mutual inductance of the Rogowski coil M , but usually M Experimental calibration is required to determine the exact value.

[0100] Set the material properties, dimensions, excitation current and other parameters of the giant magnetostrictive rod.

[0101] Material: Terfenol-D (a common giant magnetostrictive material) Saturation magnetostriction coefficient: l s =1500×10 −6 (Under certain magnetic fields and conditions) length: LGMM =50mm diameter: DGMM =10mm Excitation current (to generate magnetic field through the coil): Excitation (This value depends on the required magnetic field strength and coil design) Excitation current Excitation The specific value of will depend on the required magnetic field strength of the giant magnetostrictive rod and the design of the coils used to generate that field.

[0102] Set the parameters of the fiber Fabry-Perot cavity, such as size, fiber type, and connection method.

[0103] Cavity length: LFP =100 μm (The distance between the two reflecting surfaces of the Fabry-Perot cavity) Fiber type: Single-mode fiber (SMF-28, for example) Connection method: The optical fiber is connected to both ends of the Fabry-Perot cavity through optical fiber connectors (such as FC / PC) to ensure that light can be efficiently transmitted between the optical fiber and the Fabry-Perot cavity.

[0104] Reflective surface material: A high reflectivity film (such as gold or silver) is usually coated on the end face of the optical fiber to form a reflective surface.

[0105] Fiber Fabry-Perot cavity length L FPis one of the key parameters because it determines the periodicity and sensitivity of the interference pattern. Changes in cavity length can be accurately detected by measuring the shift of the interference pattern.

[0106] S4, perform numerical simulation; Run the simulation software and perform numerical simulation according to the set parameters.

[0107] Analyze the parameters such as the induced voltage generated by the Rogowski coil, the strain distribution of the giant magnetostrictive rod, and the change in the cavity length of the fiber Fabry-Perot cavity.

[0108] S5. Data verification; Compare the simulation results with the theoretical values ​​to verify the accuracy of the model.

[0109] S6. Optimize design.

[0110] The design of the sensor is optimized based on the simulation results to improve its performance.

[0111] Application scenarios of the fiber optic Fabry-Perot cavity current sensor based on Rogowski coil of the present invention: Power system monitoring: In high-voltage transmission lines, the sensor can be used to monitor the current on the transmission line in real time, helping power companies to manage loads, diagnose faults and manage maintenance. In addition, it can also be used to monitor the current status inside the substation to ensure the stable operation of the power system.

[0112] Railway track monitoring: The sensor can be installed on railway tracks to monitor the load and speed of trains in real time. This helps improve the safety of train operation and also helps railway departments with maintenance and fault prediction.

[0113] Structural health monitoring of bridges and buildings: By installing this sensor on bridges, buildings or other important infrastructure, the tiny deformation and stress distribution of these structures can be monitored in real time, thereby assessing their health status and detecting potential problems in a timely manner.

[0114] Oil and Gas Pipeline Monitoring: Installing this sensor on oil and gas pipelines can help monitor fluid flow and pressure in the pipeline, thereby ensuring the safe operation of the pipeline and preventing leaks and other accidents.

[0115] Dam and Reservoir Monitoring: The sensor can be used to monitor the structural health of dams, reservoirs and other water conservancy facilities. For example, by monitoring the displacement changes of a dam, its safety can be assessed and potential catastrophic events can be prevented.

[0116] Wind turbine monitoring: Installing this sensor on the blades and tower of a wind turbine can help monitor the load and strain distribution of the wind turbine, thereby improving the efficiency and reliability of wind power generation.

[0117] Applications in the aerospace industry: The sensor could be used to monitor the structural health of airplanes, helicopters and other aircraft, such as by detecting tiny deformations in wings and tails to assess their safety and prevent potential failures.

[0118] Applications in medical equipment: In medical devices, the sensor can be used to monitor patients' vital signs, such as electrocardiogram (ECG) monitoring, respiratory monitoring, etc.

[0119] Therefore, the fiber optic Fabry-Perot cavity current sensor based on the Rogowski coil of the present invention has a wide range of application prospects and can play an important role in many fields. With the advancement of technology and the reduction of costs, it is expected that the sensor will be applied in more fields.

[0120] In summary, the fiber optic Fabry-Perot cavity current sensor based on the Rogowski coil of the present invention can measure large pulse current, lightning current, short-circuit current by using the Rogowski coil, and has the advantages of large dynamic range of measurable current and wide frequency band, and well solves the problems of magnetic saturation, small measurement dynamic range, narrow frequency band, etc. encountered when measuring large current by simply using giant magnetostrictive materials and fiber grating.

[0121] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An optical fiber Fabry-Perot cavity current sensor based on Rogowski coil, characterized in that: The invention comprises a Rogowski coil (1), which is sleeved on an OPGW optical cable (2) and electrically connected to a giant magnetostrictive rod (5); an optical fiber Fabry-Perot cavity (4) is arranged at one end of the giant magnetostrictive rod (5); an optical fiber (3) connected to a demodulator is arranged to penetrate the optical fiber Fabry-Perot cavity (4); The current on the OPGW optical cable (2) is converted into an induced voltage through a Rogowski coil (1) and acts on a giant magnetostrictive rod (5), causing the giant magnetostrictive rod (5) to generate strain, thereby stretching or compressing the optical fiber Fabry-Perot cavity (4). By changing the cavity length, the wavelength corresponding to the generated interference fringes drifts, and the current of the OPGW optical cable (2) is monitored by monitoring the wavelength drift.

2. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 1, characterized in that: The positive and negative poles of the output wire of the Rogowski coil (1) are connected to the positive and negative pole ports of the driving coil (6) respectively; the driving coil (6) is wound around the giant magnetostrictive rod (5); and the giant magnetostrictive rod (5) is stacked on the optical fiber Fabry-Perot cavity (4).

3. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 2, characterized in that: Magnetic field strength generated in the middle of the Rogowski coil (1) for: in, is the axial length of the solenoid coil; is the total number of turns of the solenoid coil; is the transformation efficiency; It is the current to be measured of OPGW optical cable.

4. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 1, characterized in that: The strain generated by the giant magnetostrictive rod (5) is transmitted to the FP cavity of the optical fiber (3), causing the FP cavity length to change. The wavelength change monitored by the demodulator is used to obtain the corresponding optical fiber Fabry-Perot cavity length change, and finally the relationship between the magnitude of the current to be measured in the OPGW optical cable (2) and the wavelength change is obtained.

5. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 4, characterized in that: The FP cavity of the optical fiber (3) is fixed on the giant magnetostrictive rod (5) in the longitudinal direction as a sensing head.

6. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 5, characterized in that: The change in cavity length when the optical fiber (3) is axially strained for: in, is the sensor length, is the original length of the Fabry-Perot cavity, is the length after axial strain, is the strain coefficient.

7. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 6, characterized in that: The relationship between the magnetostrictive strain of the giant magnetostrictive rod (5) along the axial direction and the external magnetic field is: in, is the expansion coefficient of the magnetostrictive material, is the gauge factor, is the original length of the Fabry-Perot cavity, is the change in cavity length, is the magnetic field strength generated in the middle of the Rogowski coil.

8. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 4, characterized in that: The wavelength change detected by the demodulator The relationship between the change in the length of the corresponding fiber Fabry-Perot cavity is: in, is the initial length of the Fabry-Perot cavity, is the change in the length of the Fabry-Perot cavity, is the wavelength of incident light.

9. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 4, characterized in that: OPGW optical cable (2) current to be measured The size and wavelength change The relationship between them is: in, is the transformation efficiency; is the axial length of the solenoid coil; is the total number of turns of the solenoid coil; is the sensor length; is the expansion coefficient of the magnetostrictive material.

10. The optical fiber Fabry-Perot cavity current sensor based on Rogowski coil according to claim 1, characterized in that: The giant magnetostrictive rod (5) and the optical fiber Fabry-Perot cavity (4) are fixed inside the shell.

11. The method for using the fiber optic Fabry-Perot cavity current sensor based on a Rogowski coil according to any one of claims 1 to 10, characterized in that: The following steps are involved: The Rogowski coil is mounted on the OPGW optical cable and electrically connected to the giant magnetostrictive rod; one end of the giant magnetostrictive rod is connected to the optical fiber Fabry-Perot cavity, and the optical fiber is ensured to be arranged in the optical fiber Fabry-Perot cavity, and the optical fiber demodulator at the other end is connected to the monitoring equipment; When current flows through the OPGW optical cable, the Rogowski coil converts the current into an induced voltage, which acts on the giant magnetostrictive rod. The induced voltage causes the giant magnetostrictive rod to produce strain, thereby stretching or compressing the optical fiber Fabry-Perot cavity to produce interference fringes, and the corresponding wavelength drifts. Real-time monitoring of the OPGW optical cable current is achieved by monitoring the wavelength drift, and current data is determined by the obtained wavelength drift; the operating status of the power system is determined based on the monitored current data.

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