High-voltage cable sheath circulation monitoring device based on Faraday magneto-optical effect

Abstract

The invention discloses a high-voltage cable sheath circulating current monitoring device based on a Faraday magneto-optical effect, which comprises a light source excited to emit light, one end of a coupler is connected with the light source and one end of a first photoelectric detector, and the other end of the coupler is connected with one end of a polarizer; one end of the beam splitter is connected with the other end of the polarizer and one end of the second photoelectric detector, and the other end of the beam splitter is connected with one end of the polarization beam splitter, and the other end of the polarization beam splitter is connected with one end of the polarization light switch. The other end of the polarized light switch is respectively connected with the A-phase operation current sensing unit, the B-phase operation current sensing unit, the C-phase operation current sensing unit and the Ln joint sheath ring current sensing unit; and the acquisition control circuit is respectively connected with the light source, the other end of the first photoelectric detector, the other end of the second photoelectric detector and the polarized light switch. According to the invention, one monitoring device is used for simultaneously monitoring the sheath circulation signals of a plurality of measuring points and the operating currents of A, B and C phases, and the cost is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of high-voltage cable sheath circulating current detection, and in particular relates to a high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect. Background Art

[0002] With the continuous development of urban construction in my country, high-voltage overhead lines can no longer meet the requirements of current urban construction planning. Compared with overhead lines, cable tunnels using cross-linked polyethylene high-voltage cables save a lot of urban space and can also avoid power accidents caused by lightning weather and human factors. The construction scale and length are constantly increasing. The metal sheath of the cable is an important part of the cable. If current flows through the high-voltage cable during normal operation, voltage will be induced in the metal sheath of the cable. In order to ensure safe operation and suppress the grounding loop of the cable sheath, the cable metal sheath is generally grounded by single-end grounding or cross-connection. When the insulation of the cable is in good condition, the sheath circulation current is close to zero; however, if the insulation of the outer sheath is in poor condition, the grounding is poor, the metal sheath grounding method is incorrect, or the insulation sheath is aged or damaged after long-term operation, the metal sheath may be grounded at multiple points, and the grounding circulation current will increase significantly. If not handled in time, it will cause many hazards: 1) It causes local high-temperature loss and heating of the cable insulation, accelerates insulation aging, reduces the service life of the cable, and in severe cases, causes direct breakdown and grounding faults in the cable; 2) It causes the outer sheath of the cable to be damaged, resulting in multiple grounding points; 3) It directly affects the current carrying capacity, resulting in large power loss, waste of resources, etc. Therefore, monitoring the grounding circulation current of the cable sheath can not only monitor the status of the metal sheath of the power cable itself, but also monitor the quality status of the main insulation and other faults of the high-voltage power cable to ensure the long-term temperature operation of the high-voltage cable.

[0003] At present, the commonly used high-voltage cable sheath current monitoring system is mainly composed of a sheath circulation sensor, a current acquisition device and an integrated monitoring host. The sheath circulation sensor is installed on the metal shielding layer grounding wire of the direct grounding box, the cross-connection box, and the protective grounding box to collect the sheath grounding current signal. When there is an abnormal change in the sheath grounding current, an alarm is issued in time. The long-term change trend of the sheath grounding current can also be monitored to issue a trend alarm to ensure the safe operation of the cable. Such a sheath circulation monitoring system has been widely used, but in the process of engineering design and operation, it is found that power supply problems of the devices in the pipe gallery are more common. The sheath circulation collector is an active device, and the power supply problem needs to be considered. Many pipe corridors, especially the earlier ones, are not adequately equipped with power supplies. If the power lead of the collector is too long, the terminal voltage will be reduced, affecting the normal operation of the sheath collector. Some special areas where it is inconvenient to lay power cables require the device to support low-voltage power supply, which has strict requirements on the power consumption of the device. Some pipe corridors do not have power supply conditions and need to use coil energy extraction or configure batteries. However, coil energy extraction has a working dead zone and will fail when the current running on the cable is small. The battery has limited capacity and ages quickly, and needs to be replaced regularly, making operation and maintenance difficult. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a high-voltage cable sheath circulating current monitoring device based on the Faraday magneto-optical effect to solve the problem of difficulty in monitoring the high-voltage cable sheath current.

[0005] To solve the above technical problems, the present invention is implemented by adopting the following solutions: The invention provides a high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect, comprising a collection unit and a plurality of sensing units; the collection unit comprises a light source, a coupler, a polarizer, a beam splitter, a polarization beam splitter, a polarization light switch, a first photodetector, a second photodetector and a collection control circuit; the light source is stimulated to emit light; one end of the coupler is respectively connected to the light source and one end of the first photodetector, and the other end is connected to one end of the polarizer; one end of the beam splitter is respectively connected to the other end of the polarizer and one end of the second photodetector, and the other end is connected to one end of the polarization beam splitter; the other end of the polarization beam splitter is connected to one end of the polarization light switch; the other end of the polarization light switch is respectively connected to an A-phase operating current sensing unit, a B-phase operating current sensing unit, a C-phase operating current sensing unit and an L-phase operating current sensing unit. n Joint sheath circulating current sensing unit, A phase running current sensing unit, B phase running current sensing unit, C phase running current sensing unit and L nThe joint sheath circulating current sensing unit is used to measure the operating current of the A-phase cable, the B-phase cable, the C-phase cable and the sheath circulating current on the grounding wire at the cable joint. The acquisition control circuit is respectively connected to the light source, the first photodetector, the other end of the second photodetector and the polarization switch, and is used to drive the light source to emit light, control the working state of the polarization switch, and collect and process the two-way interference light signals transmitted by the first photodetector and the second photodetector; wherein n is a positive integer.

[0006] Optionally, the A phase running current sensing unit, the B phase running current sensing unit, the C phase running current sensing unit and the L n The structure of the joint sheath circulation sensing unit is the same, including: A transmission optical cable, one end of which is connected to the other end of the polarization switch, and is used to transmit the incident orthogonal linear polarization light to the λ / 4 wave plate; A λ / 4 wave plate, connected to the other end of the transmission optical cable, is used to convert the incident orthogonal linear polarization into two orthogonal circular polarizations; The sensing fiber is connected to a λ / 4 wave plate and is used to transmit two orthogonal circularly polarized lights and superimpose the phase shift produced by the measured current; The Faraday rotating mirror is located at the end of the sensing optical fiber and is used to reflect two orthogonal circularly polarized lights so that the two orthogonal circularly polarized lights return and are transmitted along the sensing optical fiber, and to introduce a phase shift to the two orthogonal circularly polarized lights to achieve passive phase bias.

[0007] Optionally, the transmission optical cable is a polarization-maintaining optical cable, and the maximum length of the transmission optical cable exceeds 10 km.

[0008] Optionally, the sensing optical fiber is arranged in a closed ring with the measured conductor corresponding to the sensing unit as the center, and the measured conductor is a single high-voltage cable or a three-phase cable grounding wire bundled as a whole.

[0009] Optionally, the polarization optical switch is a multi-channel 1×N optical switch, and one end of the polarization optical switch has one input and the other end has N outputs.

[0010] Optionally, the polarization switch switches among its multiple output terminals in sequence according to a preset timing, and measures the A, B, and C phase operating currents and the sheath circulating current on the grounding wire at the cable joint in a polling manner. The switching timing is: When the current is 0, switch to the first output terminal and connect the A-phase running current sensing unit; When the current is 0, switch to the second output terminal and connect the B phase running current sensing unit; When the current is 0, switch to the third output terminal and connect the C phase running current sensing unit; When switching to the output terminal n+3, connect Ln Joint sheath circulation sensing unit; When the current is equal to the phase A, switch back to the first output terminal and connect the A-phase running current sensing unit; The polling period is several minutes.

[0011] Optionally, the first photodetector and the second photodetector receive interference signals from the coupler and the beam splitter respectively, and the interference signals are: Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; in, , , , , To connect the A, B, C phase running current sensing unit and L n-1 , L n The system normalized light intensity when the joint sheath is circulating the sensing unit, , , , , , , , , , Connect the A, B, C phase running current sensing units and L n-1 , L n The joint sheath circulation sensing unit is the conversion coefficient of the first photodetector and the second photodetector, V is the Verdet constant of the sensing optical fiber, , , , , is the winding number of each sensing optical fiber, , , , , They are the operating currents of the A, B, and C phase cables and the sheath circulating currents on the grounding wires at the n-1 and n group cable joints. , , , , They are A, B, C phase running current sensing units and L n-1 , L n The rotation angle of the Faraday rotator mirror in the joint sheath circulation sensing unit.

[0012] Optionally, when , , , , When the set value is approached, the acquisition control circuit will collect the interference light signals according to the two opposite changes. and , normalized and signal processed, the measured current is obtained as: Inside, ; Inside, ; Inside, ; Inside, ; Inside, .

[0013] Optionally, when an abnormal sheath circulating current on the grounding wire at a phase cable joint occurs, the phase relationship between the abnormal circulating current and the operating current of phases A, B, and C is compared. When the abnormal circulating current is consistent with the operating current of a phase, the phase cable is determined to be a faulty cable.

[0014] Beneficial Effects 1. The present invention uses a polarization beam splitter based on the Faraday magneto-optical effect to realize the time-sharing measurement of the sheath circulating current of each phase. One monitoring device simultaneously monitors the sheath circulating current signals of multiple measuring points and the operating currents of the three phases A, B, and C, which meets the sheath circulating current monitoring requirements while greatly reducing the cost of the entire device.

[0015] 2. The beam splitter, polarization beam splitter and sensing unit with Faraday rotation mirror in the present invention constitute an optical sensor with a reciprocal structure. The paths through which the two beams of orthogonal polarized light in the optical path system pass are basically the same. The optical path system has good reciprocity and strong anti-interference ability. The influence of environmental factors such as vibration, stress and temperature on the optical sensor can be basically eliminated.

[0016] 3. The present invention introduces a passive phase bias through a Faraday rotating mirror to enable the optical sensor to operate at a point with higher response sensitivity, avoiding the use of expensive and unreliable LiNbO3 phase modulators or PZT phase modulators with poor temperature stability and complex modulation and demodulation circuits and algorithms. The system structure and implementation method are simpler, the cost can be greatly reduced, and the reliability is higher.

[0017] 4. The transmission optical cable of the present invention can be more than 10 km long, and the monitoring device is remotely arranged in the substation, which solves the problem of difficult power supply in the pipeline corridor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a schematic structural diagram of a high-voltage cable sheath circulating current monitoring device based on the Faraday magneto-optical effect provided in Example 1 of the present invention; Figure 2 It is a schematic diagram of a collection control circuit in a high-voltage cable sheath circulating current monitoring device based on the Faraday magneto-optical effect provided in Example 1 of the present invention; In the figure: 1. Collection unit; 2. Transmission optical cable; 3. A phase running current sensing unit; 4. B phase running current sensing unit; 5. C phase running current sensing unit; 6. L1 joint sheath circulating current sensing unit; 7. L2 joint sheath circulating current sensing unit; 8. L n Connector sheath circulation sensing unit; 11. light source; 12. coupler; 13. polarizer; 14. beam splitter; 15. polarization beam splitter; 16. polarization light switch; 17. first photodetector; 18. second photodetector; 19. acquisition control circuit; 31. λ / 4 wave plate; 32. sensing optical fiber; 33. Faraday rotation mirror; 101. FPGA module; 102. DSP module; 103. AD / DA conversion module; 104. human-machine interface module; 105. communication module; 201. light source driving functional element; 202. optical switch control functional element; 203. optical signal acquisition functional element; 204. current solution functional element; 205. sheath circulation state determination functional element. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0020] 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 by specific circumstances.

[0021] 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" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0022] Example 1 like Figure 1 As shown, this embodiment provides a high-voltage cable sheath circulating current monitoring device based on the Faraday magneto-optical effect, including a collection unit 1, a transmission optical cable 2, an A-phase operating current sensing unit 3, a B-phase operating current sensing unit 4, a C-phase operating current sensing unit 5, an L1 joint sheath circulating current sensing unit 6, an L2 joint sheath circulating current sensing unit 7 and an L n Joint sheath circulating current sensing unit 8; wherein, the A phase running current sensing unit 3, the B phase running current sensing unit 4, and the C phase running current sensing unit 5 are used to measure the running current on the A, B, and C phase high voltage cables, and are used to assist in determining the abnormal sheath circulating current phase sequence; the L1 joint sheath circulating current sensing unit 6, the L2 joint sheath circulating current sensing unit 7 to L n The joint sheath circulating current sensing unit 8 is used to measure the L1 cable joint, L2 cable joint to L n Sheath circulating current on the grounding wire at the cable joint.

[0023] The collection unit 1 is connected to the sensor units 3 to 8 via a transmission optical cable 2. The collection unit 1 includes but is not limited to a light source 11, a coupler 12, a polarizer 13, a beam splitter 14, a polarization beam splitter 15, a polarization light switch 16, a first photodetector 17, a second photodetector 18 and a collection control circuit 19.

[0024] Transmission cable 2 is a polarization-maintaining cable. The number of polarization-maintaining cable cores includes but is not limited to 6. The actual number of cores is determined by the number of test points to be tested. The maximum supported length can exceed 10km. The transmission cable 2 can be more than 10km long. The monitoring device is remotely arranged in the substation, solving the problem of difficult power supply in the pipe gallery.

[0025] The coupler 12 includes but is not limited to at least one of a beam splitter, an optical circulator, and a 2×2 coupler. The beam splitter 14 includes but is not limited to at least one of a polarization-maintaining fiber beam splitter or a polarization-maintaining fiber coupler.

[0026] The two ports on the left side of the coupler 12 are the first and second ends on the left side, and the two ports on the right side are the first and second ends on the right side. The two ports on the left side of the beam splitter 14 are the first and second ends on the left side, and the one port on the right side is the right end.

[0027] The first left end of the coupler 12 is connected to the light source 11, and the second left end of the coupler 12 is connected to the first photodetector 17. The second right end of the coupler 12 can be left vacant or connected to another photodetector ( Figure 1 (not shown).

[0028] One end of the polarizer 13 is connected to the first end on the right side of the coupler 12, and the other end of the polarizer 13 is connected to the first end on the left side of the beam splitter 14. The right end of the beam splitter 14 is connected to the left end of the polarization beam splitter 15. The second end on the left side of the beam splitter 14 is connected to the second detector 18.

[0029] The polarization switch 16 is a multi-channel 1×N optical switch, with 1 input at the left end and N outputs at the right end. The left end of the polarization switch 16 is connected to the right end of the polarization beam splitter 15, and the right ends of the polarization switch are respectively connected to the A-phase operating current sensing unit 3, the B-phase operating current sensing unit 4, the C-phase operating current sensing unit 5, the L1 joint sheath circulating current sensing unit 6, the L2 joint sheath circulating current sensing unit 7 to the L n Joint sheath circulation sensing unit 8.

[0030] The A-phase operating current sensing unit 3 is connected to the first end on the right side of the polarization light switch 16, the B-phase operating current sensing unit 4 is connected to the second end on the right side of the polarization light switch 16, the C-phase operating current sensing unit 5 is connected to the third end on the right side of the polarization light switch 16, the L1 connector sheath circulating current sensing unit 6 is connected to the fourth end on the right side of the polarization light switch 16, the L2 connector sheath circulating current sensing unit 7 is connected to the fifth end on the right side of the polarization light switch 16, and so on. n The joint sheath circulating current sensing unit 8 is connected to the n+3th terminal on the right side of the polarization light switch 16, where n is a positive integer.

[0031] The A-phase running current sensing unit 3 includes a λ / 4 wave plate 31, a sensing optical fiber 32, and a Faraday rotating mirror 33. The measured conductor is the A-phase high-voltage cable body. The composition of the sensing units 4 to 8 is consistent with that of the A-phase running current sensing unit 3. The measured conductors of the B-phase and C-phase running current sensing units 4 and 5 are the B-phase and C-phase high-voltage cable bodies, respectively. n The measured conductors of the joint sheath circulating current sensing units 6 to 8 are respectively the three-phase grounding wires at each cable joint that are bundled as a whole.

[0032] The left end of the transmission optical cable 2 is connected to the right end of the polarization switch 16 for transmitting the incident orthogonal linear polarization; the λ / 4 wave plate 31 is connected to the right end of the transmission optical cable 20, including but not limited to fusion, for converting the incident orthogonal linear polarization into two orthogonal circular polarizations. The sensing optical fiber 32 is connected to the λ / 4 wave plate 31, including but not limited to fusion, for transmitting two orthogonal circular polarizations and superimposing the phase shift generated by the measured current. The sensing optical fiber 32 is respectively connected to the A, B, C phase high voltage cable or L1~L n The center of the grounding wire at the cable joint is arranged in a closed ring (the cable can be allowed to deviate from the center), so as to detect the cable sheath circulating current and three-phase operating current at each cable joint. The Faraday rotating mirror 33 is located at the end of the sensing optical fiber 32, reflecting two orthogonal circularly polarized lights, making them (i.e., two orthogonal circularly polarized lights) return and transmit along the sensing optical fiber 32, and at the same time introducing a specific phase shift to the two orthogonal circularly polarized lights to realize passive phase bias.

[0033] The Faraday rotation mirror 33 includes but is not limited to a collimating lens, a Faraday rotator and a reflector. Preferably, the Faraday rotator rotates the polarization plane of the polarized light by 22.5° in a single pass.

[0034] The acquisition control circuit 19 is connected to the light source 11, the polarization switch 16, the first photodetector 17, and the second photodetector 18 by electrical signals, drives the light source 11 to emit light, controls the working state of the polarization switch 16, acquires and processes the two-way interference light signals transmitted by the first photodetector 17 and the second photodetector 18, calculates the measured current of the primary conductor located in each sensing unit according to a specific algorithm, and determines the circulating current state and phase of the cable sheath.

[0035] like Figure 2As shown, the acquisition control circuit 19 includes hardware devices such as an FPGA module 101, a DSP module 102, an AD / DA conversion module 103, a human-machine interface module 104, and a communication module 105. The DSP module 102 is the main control module of the device, and the control device realizes functions such as human-machine interaction, setting of fixed values, FPGA management, and external communication. The AD / DA conversion module 103 is connected to the light source 11 and the polarization light switch 16 respectively, completes the digital-to-analog conversion of the FPGA light source drive signal and the optical switch control signal, and realizes the driving of the light source 11 and the switching timing control of the polarization light switch 16; at the same time, a high sampling rate analog-to-digital conversion chip (sampling rate ≥ 20Mbps) is configured to collect the signals output by the first photodetector 17 and the second photodetector 18, complete the analog-to-digital conversion, and send it to the FPGA module 101 to realize the acquisition of the optical signal carrying the measured current information. The FPGA module 101 implements the main computing function of the device, and can be subdivided into a light source driving function element 201, an optical switch control function element 202, an optical signal acquisition function element 203, a current solution function element 204, and a circulating current state determination function element 205. The communication module 105 realizes communication with the monitoring background or other devices through an optical port or an electrical port.

[0036] Example 2 This embodiment provides a method for monitoring the circulating current of a high-voltage cable sheath based on the Faraday magneto-optical effect. The high-voltage cable sheath circulating current monitoring device based on the Faraday magneto-optical effect described in Example 1 is used for monitoring. The process is as follows: The driving circuit of the acquisition control circuit 19 drives the light source 11 to emit light upon stimulation, and the coupler 12 guides the light signal output by the light source 11 to the first end on the right side of the coupler 12, and inputs it into the polarizer 13 to generate linear polarization; after the linear polarization passes through the beam splitter 14 and the polarization beam splitter 15, it is divided into two incident orthogonal linear polarization beams with the same propagation direction; after the two incident orthogonal linear polarization beams pass through the polarization switch 16, they are respectively input into the sensing units 3-8 in sequence; after the two incident orthogonal linear polarization beams in the transmission optical cable 2 pass through the λ / 4 wave plate 31, two orthogonal circular polarization beams are output. The two orthogonal circular polarization beams are transmitted along the sensing optical fiber 32. Due to the Faraday magneto-optical effect generated by the running current or the sheath circulation in the conductor being measured, the propagation speed of one of the two orthogonal circular polarization beams becomes faster and the propagation speed of the other becomes slower, thereby generating a phase difference. The two orthogonal circularly polarized lights are reflected by the Faraday rotation mirror 33 with a rotation angle of θ at the end of the sensing optical fiber 32, and the phase difference of the two orthogonal circularly polarized lights increases again by 2θ. Due to the effect of the mirror, the polarization modes of the two orthogonal circularly polarized lights are interchanged, the left-handed circularly polarized light becomes the right-handed circularly polarized light, and the right-handed circularly polarized light becomes the left-handed circularly polarized light, and returns along the original path.

[0037] When the two orthogonal circularly polarized lights return, the direction of the magnetic field of the measured current remains unchanged, while the propagation direction of the two returned orthogonal circularly polarized lights changes and the polarization state changes, so the phase difference caused by the Faraday effect will double, and the phase difference introduced by the Faraday rotator will also double. After passing through the λ / 4 wave plate 31 again, it becomes two returned orthogonal linear polarized lights, and the polarization directions are interchanged during the relative forward process. The two returned orthogonal linear polarized lights pass through the polarization switch 16 and the polarization beam splitter 15 to become a combined polarized light, and then pass through the beam splitter 14 to be divided into two orthogonal linear polarized lights that propagate separately. The first end on the left side of the beam splitter 14 outputs a beam of linear polarized light that reaches the polarizer 13 and is polarized, and then reaches the first photodetector 17 through the second end on the left side of the coupler 12, which is the first interference light signal; the second end on the left side of the beam splitter 14 outputs another beam of polarized light that reaches the second photodetector 18, which is the second interference light signal. A polarizer can also be connected between the beam splitter 14 and the second photodetector 18 to add a polarization analysis function.

[0038] The first photodetector 17 performs photoelectric conversion on the first interference light signal and outputs a first electrical signal. The second photodetector 18 performs photoelectric conversion on the second interference light signal and outputs a second electrical signal. The acquisition control circuit 19 receives and demodulates the first electrical signal and the second electrical signal, and determines the measured current or circulating current on the corresponding conductor in the corresponding sensing unit 3-8 based on the first electrical signal and the second electrical signal and according to the optical switch timing.

[0039] The polarized light X-ray and the polarized light Y-ray output from the polarization beam splitter 14 have their polarization states interchanged when returning to the polarization beam splitter 14, and the optical path of the entire interference optical path system is reciprocal. After the polarization beam splitter 14, the optical path of the entire interference optical path system is reciprocal, and the paths of the two orthogonal polarized lights are the same. The optical path system has good reciprocity and strong anti-interference ability, and the influence of environmental factors such as vibration, stress and temperature on the optical current sensor can be basically eliminated.

[0040] The light source driving functional element 201 of the FPGA module 101 in the acquisition control circuit 19 outputs a driving signal to drive the light source to emit light. Optimally, the light source driving element 201 can collect the operating data of the light source 11, realize light source feedback control, optimize the driving strategy, and ensure that the light source 11 is always in the best working state.

[0041] The optical switch control function element 202 controls the polarization optical switch 16 to switch between the optical ports according to the preset timing, thereby connecting the sensor units 3 to 8 respectively, and measuring the A, B, C phase operating current and L1 to L2 in a polling manner. n The switching sequence of the cable sheath circulating current of the cable joint grounding wire is: When the A phase current sensor unit is connected, switch to the first end on the right side; When the current sensor unit is switched to the second end on the right, it is connected to the B-phase running current sensing unit; When the current is on, switch to the third terminal on the right and connect the C-phase running current sensing unit; When the switch is on, switch to the fourth end on the right and connect the L1 connector sheath circulation sensing unit; When the switch is on, switch to the fifth end on the right and connect the L2 connector sheath circulation sensing unit; ······ When switching to the right side n+3 end, connect L n Joint sheath circulation sensing unit; When the current sensor unit is on, switch back to the first end on the right side and connect the A-phase running current sensing unit; hour,······ Preferably, the polling cycle of the polarization switch 16 is several minutes. Maintain for about hundreds of milliseconds, , ······ and The length is consistent.

[0042] The acquisition control circuit 19 determines which sensing unit the measured current belongs to according to the time sequence, and outputs the measured current signal of the corresponding phase sequence. Specifically, the optical signal acquisition functional element 203 collects the digital signal output by the AD / DA conversion module 103, performs filtering, averaging and other processing, and then sends it to the current solution functional element 204. The current solution component 204 simultaneously receives the optical switch state signal output by the optical switch control element 202, determines in real time which optical fiber sensing unit the current signal belongs to, calculates the sheath circulating current on the measured conductor, and outputs the calculated current to the sheath circulating current state determination functional element 205.

[0043] Assume that the polarization switch 16 is in At this moment, the acquisition unit 1 is connected to the A-phase running current sensing unit 2, and the optical signal returned to the first photodetector 17 is: (1) in, is the normalized initial light intensity of the system when the A-phase operating current sensing unit 2 is connected, V is the Verdet constant of the sensing optical fiber, is the winding number of the A-phase sensing optical fiber, is the operating current on the A-phase cable, is the rotation angle of the A-phase Faraday rotator, is a coefficient related to the insertion loss of the first end on the left side of the coupler 12 and the beam splitter 14 (ie, the conversion coefficient of the first photodetector when the A-phase operating current sensing unit 2 is connected).

[0044] Since the polarization directions of the output lights from the ports of the beam splitter 14 corresponding to the first photodetector 17 and the second photodetector 18 are orthogonal, the signals of the first photodetector 17 and the second photodetector 18 are and The change is reversed and returns to the second photodetector 18 as: (2) in is a coefficient related to the insertion loss at the second end on the left side of the beam splitter 14 .

[0045] When the rotation angle of the Faraday rotator 33 When , the signals of the first photodetector 17 and the second photodetector 18 become: (3) (4) At this time, the maximum modulation depth of light intensity is achieved, and the current sensing system has the maximum sensitivity. According to the two detector signals, the measured current information can be accurately obtained by using a suitable demodulation algorithm, while eliminating the influence of system optical power fluctuations, electromagnetic interference, and reducing the influence of external interference factors such as vibration and temperature. The demodulation algorithm for solving the primary current includes but is not limited to the following algorithms: 1. After normalization, the sum of equation (3) and equation (4) can obtain the parameters of the light intensity of the system: (5) 2. After normalization, the difference between equation (3) and equation (4) can be used to obtain the change signal related to the current: (6) 3. According to equations (5) and (6), the measured current information can be obtained: (7) Similarly, when the polarization switch 16 is in , , , ····· At the time, when the acquisition unit 1 is connected to the sensor units 3 to 8 respectively, the optical signals returned to the first photodetector 17 and the second photodetector 18 are: , (8) , (9) , (10) , (11) , (12) , (13) , (14) , (15) ······ , (16) , (17) in, , , , , To connect the B and C phase operating current sensing units and L1, L2, L n The system normalized light intensity when the joint sheath is circulating the sensing unit, , , , , , , , , , Connect the B and C phase operating current sensing units and L1, L2, L n The joint sheath circulation sensing unit is the conversion coefficient of the first photodetector and the second photodetector, V is the Verdet constant of the sensing optical fiber, , , , , is the winding number of each sensing optical fiber, , , , , They are respectively the operating current of the B-phase and C-phase cables and the L1, L2, L n Sheath circulation, , , , , For the B phase, C phase running current sensing unit and L1, L2, L n The rotation angle of the Faraday rotator mirror in the joint sheath circulation sensing unit; when the rotation angle of the Faraday rotator mirror , , , , When it is close to 22.5°, the acquisition control circuit will collect the interference light signals according to the two opposite changes. and , after normalization and signal processing, the information of the measured current is: , (18) , (19) , (20) , (twenty one) ······ , (twenty two) Because L1, L2...L n The three-phase grounding wires at the grounding point measured by the joint sheath circulation sensing unit are bundled and passed through the current sensor units 6~8 as a whole, so the sheath circulation detected by the system is the data of the three-phase sheath circulation combined. When the sheath circulation on a phase cable grounding wire is abnormal, the abnormal phase sequence cannot be directly locked through the sheath circulation data. By comparing the phase relationship between the abnormal circulation and the A, B, and C phase operating currents, it can be determined that the abnormal circulation is consistent with the phase of the phase operating current, and the phase cable is a faulty cable, so that the faulty cable can be accurately determined.

[0046] It is worth noting that the λ / 4 wave plate 31 in the embodiment of the present invention can also be a half-wave plate. In this case, the two beams of light entering the sensing optical fiber 32 become orthogonal linear polarization. In the process of the two orthogonal linear polarizations passing through the sensing optical fiber 32 and the Faraday rotating reflector 33, the current causes the two orthogonal linear polarizations to produce Faraday deflection, and the Faraday rotating reflector 33 also introduces a phase offset of 4θ to the two linear polarizations. The current information is also included in the first interference signal and the second interference signal, and the above demodulation method is still applicable.

[0047] The sheath circulating current state determination function element 205 records the original waveform of the sheath circulating current, and makes state determinations on the sheath circulating current amplitude, change amount, change speed, etc. It issues an alarm in time when there is an abnormal change in the sheath grounding current, and can also issue a trend alarm by monitoring the long-term change trend of the sheath grounding current.

[0048] In summary, the present invention aims at the problems of unstable power supply of traditional sheath circulation collector, high cost of all-fiber current sensor and stability of phase modulator, and proposes a low-cost and high-reliability solution for high-voltage cable sheath circulation monitoring device based on Faraday magneto-optical effect: a polarization beam splitter is used to realize time-sharing measurement of sheath circulation of each phase, and a monitoring device is used to monitor the sheath circulation and three-phase operating current at multiple cable joints at the same time, which meets the requirements of sheath circulation monitoring and greatly reduces the cost of the whole device; a beam splitter 14, a polarization beam splitter 16 and a current sensing unit 3~8 with a Faraday rotating reflector 33 are used to form an optical sensor with a reciprocal structure, and the optical path system The paths through which the two beams of orthogonal polarized light in the system pass are basically the same, the optical path system has good reciprocity and strong anti-interference ability, and the influence of environmental factors such as vibration, stress and temperature on the optical sensor can be basically eliminated; a passive phase bias is introduced through the Faraday rotation mirror 33 to enable the optical sensor to operate at a point with higher response sensitivity, avoiding the use of expensive and unreliable LiNbO3 phase modulators or PZT phase modulators with poor temperature stability, and there is no need to use a polarization-maintaining optical cable delay line that works with the phase modulator, as well as complex modulation and demodulation circuits and algorithms. The system structure and implementation method are simpler, the device cost can be greatly reduced, and the reliability is higher.

[0049] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect, characterized in that: The invention comprises a collection unit and a plurality of sensing units; the collection unit comprises a light source, a coupler, a polarizer, a beam splitter, a polarization beam splitter, a polarization light switch, a first photodetector, a second photodetector and a collection control circuit; the light source is stimulated to emit light; one end of the coupler is respectively connected to the light source and one end of the first photodetector, and the other end is connected to one end of the polarizer; one end of the beam splitter is respectively connected to the other end of the polarizer and one end of the second photodetector, and the other end is connected to one end of the polarization beam splitter; the other end of the polarization beam splitter is connected to one end of the polarization light switch; the other end of the polarization light switch is respectively connected to the A phase running current sensing unit, the B phase running current sensing unit, the C phase running current sensing unit and the L phase running current sensing unit. n Joint sheath circulating current sensing unit, A phase running current sensing unit, B phase running current sensing unit, C phase running current sensing unit and L n The joint sheath circulating current sensing unit is used to measure the operating current of the A-phase cable, the B-phase cable, the C-phase cable and the sheath circulating current on the grounding wire at the cable joint. The acquisition control circuit is respectively connected to the light source, the first photodetector, the other end of the second photodetector and the polarization switch, and is used to drive the light source to emit light, control the working state of the polarization switch, and collect and process the two-way interference light signals transmitted by the first photodetector and the second photodetector; wherein n is a positive integer.

2. According to claim 1, the high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect is characterized in that: A phase running current sensing unit, B phase running current sensing unit, C phase running current sensing unit and L n The structure of the joint sheath circulation sensing unit is the same, including: A transmission optical cable, one end of which is connected to the other end of the polarization switch, and is used to transmit the incident orthogonal linear polarization light to the λ / 4 wave plate; A λ / 4 wave plate, connected to the other end of the transmission optical cable, is used to convert the incident orthogonal linear polarization into two orthogonal circular polarizations; The sensing fiber is connected to a λ / 4 wave plate and is used to transmit two orthogonal circularly polarized lights and superimpose the phase shift produced by the measured current; The Faraday rotating mirror is located at the end of the sensing optical fiber and is used to reflect two orthogonal circularly polarized lights so that the two orthogonal circularly polarized lights return and are transmitted along the sensing optical fiber, and to introduce a phase shift to the two orthogonal circularly polarized lights to achieve passive phase bias.

3. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 2 is characterized in that: The transmission optical cable is a polarization-maintaining optical cable, and the maximum length of the transmission optical cable exceeds 10 km.

4. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 2 is characterized in that: The sensing optical fiber is arranged in a closed ring with the measured conductor corresponding to the sensing unit as the center. The measured conductor is a single high-voltage cable or a three-phase cable grounding wire bundled as a whole.

5. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 1 is characterized in that: The polarization optical switch is a multi-channel 1×N optical switch, with one end of the polarization optical switch having one input and the other end having N outputs.

6. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 1 is characterized in that: The polarization switch switches between its multiple output terminals in sequence according to the preset timing, and measures the A, B, and C phase operating currents and the sheath circulating current on the grounding wire at the cable joint in a polling manner. The switching timing is: When the current is 0, switch to the first output terminal and connect the A-phase running current sensing unit; When the current is 0, switch to the second output terminal and connect the B phase running current sensing unit; When the current is 0, switch to the third output terminal and connect the C phase running current sensing unit; When switching to the output terminal n+3, connect L n Joint sheath circulation sensing unit; When the current is equal to the phase A, switch back to the first output terminal and connect the A-phase running current sensing unit; The polling period is several minutes.

7. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 1 is characterized in that: The first photodetector and the second photodetector receive interference signals from the coupler and the beam splitter respectively, and the interference signals are: Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; Inside, ; in, , , , , To connect the A, B, C phase running current sensing unit and L n-1 , L n The system normalized light intensity when the joint sheath is circulating the sensing unit, , , , , , , , , , Connect the A, B, C phase running current sensing units and L n-1 , L n The joint sheath circulation sensing unit is the conversion coefficient of the first photodetector and the second photodetector, V is the Verdet constant of the sensing optical fiber, , , , , is the winding number of each sensing optical fiber, , , , , They are the operating currents of the A, B, and C phase cables and the sheath circulating currents on the grounding wires at the n-1 and n group cable joints. , , , , They are A, B, C phase running current sensing units and L n-1 , L n The rotation angle of the Faraday rotator mirror in the joint sheath circulation sensing unit.

8. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 7 is characterized in that: when , , , , When the set value is approached, the acquisition control circuit will collect the interference light signals according to the two opposite changes. and , normalized and signal processed, the measured current is obtained as: Inside, ; Inside, ; Inside, ; Inside, ; Inside, .

9. The high-voltage cable sheath circulating current monitoring device based on Faraday magneto-optical effect according to claim 1 is characterized in that: When the sheath circulating current on the grounding wire at a phase cable joint is abnormal, compare the phase relationship between the abnormal circulating current and the operating current of phases A, B, and C. When the phase of the abnormal circulating current is consistent with the operating current of a phase, the cable of that phase is determined to be a faulty cable.

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