Non-intrusive optical current transformer

Abstract

The invention relates to the field of power electronic devices, in particular to a non-intrusive optical current transformer. A first optical fiber ring and a second optical fiber ring are arranged in an isolation cavity in an annular shell, the annular shell is provided with a conductor hole through which a to-be-detected conductor penetrates, and when the to-be-detected conductor penetrates through the conductor hole, the to-be-detected conductor can pass through the first optical fiber ring and the second optical fiber ring; the first optical fiber ring and the second optical fiber ring respectively output a first optical signal and a second optical signal which are obtained by modulating an original optical signal to the signal conversion module under the action of a magnetic field of the conductor to be measured; the signal conversion module is used for respectively converting the received first optical signal and the second optical signal into a first electric signal and a second electric signal and outputting the first electric signal and the second electric signal to the signal processing module; and the signal processing module is used for processing according to the first electric signal and the second electric signal to obtain alternating current without direct current, so that direct current magnetic bias interference is eliminated, and the measurement precision is improved.

Description

Technical Field

[0001] This invention relates to the field of power electronic devices, and more specifically to a non-invasive optical current transformer. Background Technology

[0002] Currently, with the construction of power systems and the increase in grid capacity, the requirements for substations and converter stations are becoming increasingly stringent. Among these requirements, some substations and converter stations are required to add online monitoring systems. Current transformers are needed for current measurement. However, since some primary conductors at the measurement points of substations and converter stations are in an AC field, there is DC bias magnetism when measuring AC current. Moreover, the DC bias magnetism increases with the size of the AC current, causing transformer vibration and inaccurate measurement accuracy. Summary of the Invention

[0003] The purpose of this invention is to provide a non-invasive optical current transformer. This invention sets a first optical fiber ring and a second optical fiber ring in an isolation cavity within an annular housing. By processing the first optical signal and the second optical signal of the first optical fiber ring and the second optical fiber ring through a back-end acquisition device, an AC current that does not contain DC current can be obtained, thereby eliminating DC bias interference and improving measurement accuracy.

[0004] This invention provides a non-invasive optical current transformer, comprising: The mounting assembly includes a mounting bracket and an annular housing mounted on the mounting bracket. The annular housing has a conductor hole for a conductor to pass through. A flow-blocking plate is provided inside the annular housing, and the flow-blocking plate and the inner wall of the annular housing enclose an isolation cavity. The sensing component includes a first optical fiber ring and a second optical fiber ring disposed within the isolation cavity, wherein the number of optical fiber turns in the first optical fiber ring is less than that in the second optical fiber ring. Terminal assembly, including a terminal box connected to an annular housing; The back-end acquisition unit is connected to the first and second fiber optic rings via optical cables led out from the terminal box. The back-end acquisition unit includes a signal conversion module, a signal processing module, and a light source for providing raw optical signals to the first and second fiber optic rings. When the conductor under test passes through the conductor hole, the first optical fiber loop and the second optical fiber loop, under the action of the alternating magnetic field generated by the conductor under test, respectively output the first optical signal and the second optical signal modulated from the original optical signal to the signal conversion module; the signal conversion module is used to convert the received first optical signal and the second optical signal into a first electrical signal and a second electrical signal, respectively, and output them to the signal processing module. The signal processing module is used to process the first electrical signal and the second electrical signal to obtain an alternating current that does not contain direct current.

[0005] Optionally, the signal processing module is used to process the first electrical signal and the second electrical signal to obtain an alternating current that does not contain direct current, including: The signal processing module is used for: The composite AC current in the conductor under test and the estimated range of the DC current in the composite AC current are obtained based on the first electrical signal processing. The DC current in the conductor under test is obtained based on the second electrical signal; The DC current obtained from the second electrical signal is verified using the estimated range of the DC component. The verified DC current is removed from the composite AC current to obtain an AC current that does not contain DC current.

[0006] Optionally, the first fiber optic ring has 45 turns and the second fiber optic ring has 75 turns.

[0007] Optionally, the annular housing includes a lower housing and an upper housing, the outer peripheral sides of the lower housing and the upper housing are connected to each other, and the inner peripheral sides are both connected to the baffle plate; the lower housing is connected to the bottom of the terminal box, the baffle plate is an epoxy insulating component, the first optical fiber ring is disposed near the lower housing, and the second optical fiber ring is disposed near the upper housing.

[0008] Optionally, the lower housing is provided with a plurality of protrusions, and both the mounting bracket and the protrusions are provided with through holes. Fasteners can be screwed into the through holes of the mounting bracket and the protrusions to install the annular housing on the mounting bracket. By adjusting the included angle between the annular housing and the mounting bracket, it can be adapted to the corresponding conductor to be tested.

[0009] Optionally, it also includes: The protective shield comprises multiple protective shield units arranged in a circumferential array on the outside of the annular shell.

[0010] Optionally, the terminal box includes a terminal box housing and a terminal box cover plate disposed on the terminal box housing, and the pigtails of the first optical fiber ring and the second optical fiber ring are connected to the optical cable inside the terminal box housing.

[0011] Optionally, the terminal box housing is provided with an optical fiber tray and an optical cable pressure plate, and the pigtails and optical cables of the first and second optical fiber rings are embedded in the optical fiber tray and can move with the optical cable pressure plate.

[0012] Optionally, the terminal box housing is provided with an interface for a cable to pass through, and the cable is fixed to the interface by a locking connector.

[0013] Optionally, it also includes: A corrugated pipe is fitted over the cable that passes through the interface, and the cable that passes through the connector is connected to the back-end data collector under the protection of the corrugated pipe.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention incorporates a first optical fiber ring and a second optical fiber ring within an isolation cavity inside a ring-shaped housing. The ring-shaped housing has a conductor hole for the conductor under test to pass through. When the conductor under test passes through the conductor hole, under the influence of the magnetic field of the conductor under test, the first and second optical fiber rings respectively output a first optical signal and a second optical signal modulated from the original optical signal to a signal conversion module. The signal conversion module converts the received first and second optical signals into a first electrical signal and a second electrical signal, respectively, and outputs them to a signal processing module. The signal processing module processes the first and second electrical signals to obtain an alternating current that does not contain direct current, thereby eliminating DC bias interference and improving measurement accuracy. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an optical current transformer according to an embodiment of the present invention; Figure 2 for Figure 1 Horizontal sectional view; Figure 3 This is a schematic diagram of the lower housing structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the horizontal installation of an optical current transformer according to an embodiment of the present invention; Figure 5 This is a flowchart of the processing flow of the back-end data acquisition unit of the optical current transformer according to an embodiment of the present invention.

[0016] Numbering on the map: 1. Annular housing; 2. Mounting bracket; 3. Protective cover; 4. Sensing component; 5. Fiber optic tray; 6. Flow divider; 7. Fiber optic cable clamp; 8. Locking connector; 9. Corrugated tube; 10. Lower housing; 11. Terminal box housing; 12. Terminal box cover; 13. Upper housing; 14. Protrusion; 15. Conductor; 16. Second fiber optic ring; 17. First fiber optic ring. Detailed Implementation

[0017] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0019] To make the purpose, technical solution, and advantages of this invention patent clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] This embodiment provides a non-invasive optical current transformer, which includes a mounting assembly, a sensing assembly 4, a terminal assembly, and a back-end data acquisition unit. The mounting assembly includes a mounting bracket 2 and an annular housing 1 mounted on the mounting bracket 2. The mounting bracket 2 consists of two mounting plates, which can be made of channel steel. The mounting plates have multiple mounting holes, suitable for various installation methods. The mounting plates are connected by a support plate, resulting in a stable structure. The annular housing 1 has a conductor hole for the conductor 15 to be measured to pass through. In the prior art, some primary conductors, such as copper busbars and bushings, have fixed structural designs that are difficult to modify, requiring the use of existing working conditions to install current transformers. However, many measurement locations are in confined spaces, and general electronic current transformers are large, bulky, and difficult to install. In this embodiment, the diameter of the conductor hole is larger than the diameter of the conductor 15 to be measured (such as a tube, copper plate, and other devices in the art). During measurement, it does not contact the conductor 15 to be measured, enabling non-invasive measurement and is unaffected by the shape of the conductor 15 to be measured. In this embodiment, the annular shell 1 is also provided with a protective cover 3. The protective cover 3 is a spliced ​​structure. Each protective cover unit is fan-shaped, and four protective cover units are distributed circumferentially on the outer periphery of the annular shell 1 to cover the annular shell 1.

[0021] A flow-blocking plate 6 is provided inside the annular housing 1, and the flow-blocking plate 6 and the inner wall of the annular housing 1 enclose an isolation cavity; in this embodiment, the flow-blocking plate 6 is an epoxy insulating component. The flow-blocking plate 6 can effectively isolate circulating current and improve measurement accuracy. The sensing component 4 includes a first optical fiber ring 17 and a second optical fiber ring 16 disposed in the isolation cavity. The number of fiber turns in the first optical fiber ring 17 is less than that in the second optical fiber ring 16. When light propagates in the first optical fiber ring 17 and the second optical fiber ring 16, the polarization plane of the light will be deflected under the action of the magnetic field generated by the conductor. The deflection angle is proportional to the conductor current, so the conductor current can be obtained by using the optical signal output from the first optical fiber ring 17 and the second optical fiber ring 16. The sensing component 4 in this embodiment is not limited to measuring AC field conductors, but can also measure DC field conductors independently.

[0022] The terminal assembly includes a terminal box connected to the annular housing 1; both the first fiber ring 17 and the second fiber ring 16 are connected to the back-end acquisition unit via optical cables led out from the terminal box. The first fiber ring 17 has a small number of fiber turns wound on it, used to measure the range of small DC currents and composite AC currents. The first fiber ring 17 cannot directly obtain AC currents that do not contain DC currents, so it needs to be used in conjunction with the second fiber ring 16 for further processing. The second fiber ring 16 has multiple fiber turns wound on it, used for accurate measurement of small DC currents. In this embodiment, the first fiber ring has 45 turns and the second fiber ring has 75 turns.

[0023] The back-end acquisition unit includes a signal conversion module, a signal processing module, and a light source capable of providing raw optical signals to the first optical fiber ring 17 and the second optical fiber ring 16. When the conductor under test 15 passes through the conductor hole of the annular housing 1, under the action of the alternating magnetic field generated by the conductor under test 15, the first optical fiber ring 17 and the second optical fiber ring 16 respectively output the first optical signal and the second optical signal modulated from the raw optical signal to the signal conversion module; the signal conversion module is used to convert the received first optical signal and the second optical signal into a first electrical signal and a second electrical signal, respectively, and output them to the signal processing module; the signal processing module is used to process the first electrical signal and the second electrical signal to obtain an alternating current that does not contain direct current.

[0024] The signal processing module is used to process the first and second electrical signals to obtain an AC current that does not contain DC current. This includes: processing the first electrical signal to obtain a composite AC current in the conductor under test and an estimated range of the DC current within that composite AC current. The DC current value measured by the first fiber optic loop 17 is actually an inaccurate value with errors. This is because the first fiber optic loop 17 has fewer turns and lower signal strength; based on the inaccurate value and the preset error range, only an estimated range of the DC current can be determined. The module then obtains the DC current in the conductor under test based on the second electrical signal. The second fiber optic loop 16 has more turns and higher signal strength, thus obtaining an accurate value of the DC current in the conductor under test based on the second electrical signal. The estimated range of the DC component is used to verify the DC current obtained from the second electrical signal (the DC current obtained from the second electrical signal needs to be within the estimated range). Finally, the verified DC current is removed from the composite AC current to obtain an AC current that does not contain DC current, effectively improving measurement accuracy.

[0025] Specifically, the annular housing 1 includes a lower housing 10 and an upper housing 13. The outer peripheries of the lower housing 10 and the upper housing 13 are connected to each other, and their inner peripheries are both connected to the baffle plate 6. The lower housing 10 is connected to the bottom of the terminal box. The first optical fiber ring 17 is located near the lower housing 13, and the second optical fiber ring 16 is located near the upper housing 13. The lower housing 10 has multiple protrusions 14. Both the mounting bracket 2 and the protrusions 14 have through holes. Fasteners can be screwed into the through holes of the mounting bracket 2 and the protrusions 14 to mount the annular housing 1 on the mounting bracket 2. By adjusting the angle between the annular housing 1 and the mounting bracket 2, the current transformer can be adapted to the corresponding conductor under test. For example, the mounting bracket 2 is vertically fixed on the mounting plane, and the annular housing 1 can be mounted horizontally or vertically on the mounting bracket 2 to meet the measurement requirements of conductors in different positions.

[0026] The terminal box includes a terminal box housing 11 and a terminal box cover 12 covering the terminal box housing 11. The pigtails of the first fiber optic ring 17 and the second fiber optic ring 16 are connected to the optical cable inside the terminal box housing 11. The terminal box housing 11 is provided with a fiber optic tray 5 and an optical cable clamping plate 7. The pigtails of the first fiber optic ring 17 and the second fiber optic ring 16 and the optical cable are embedded in the fiber optic tray 5 and can move with the optical cable clamping plate 7. An interface for cable penetration is provided on the terminal box housing 11, and the cable is fixed to the interface via a locking connector 8. A corrugated tube 9 is fitted onto the cable penetrating the interface, and the cable penetrating the connector is connected to the downstream data acquisition unit under the protection of the corrugated tube 9.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A non-invasive optical current transformer, characterized in that, include: The mounting assembly includes a mounting bracket and an annular housing mounted on the mounting bracket. The annular housing has a conductor hole for a conductor to pass through. A flow-blocking plate is provided inside the annular housing, and the flow-blocking plate and the inner wall of the annular housing enclose an isolation cavity. The sensing component includes a first optical fiber ring and a second optical fiber ring disposed within the isolation cavity, wherein the number of optical fiber turns in the first optical fiber ring is less than that in the second optical fiber ring. Terminal assembly, including a terminal box connected to an annular housing; The back-end acquisition unit is connected to the first and second fiber optic rings via optical cables led out from the terminal box. The back-end acquisition unit includes a signal conversion module, a signal processing module, and a light source for providing raw optical signals to the first and second fiber optic rings. When the conductor under test passes through the conductor hole, the first optical fiber loop and the second optical fiber loop, under the action of the alternating magnetic field generated by the conductor under test, respectively output the first optical signal and the second optical signal modulated from the original optical signal to the signal conversion module; the signal conversion module is used to convert the received first optical signal and the second optical signal into a first electrical signal and a second electrical signal, respectively, and output them to the signal processing module. The signal processing module is used to process the first electrical signal and the second electrical signal to obtain an alternating current that does not contain direct current.

2. The non-invasive optical current transformer according to claim 1, characterized in that, The signal processing module is used to process the first electrical signal and the second electrical signal to obtain an alternating current that does not contain direct current, including: The signal processing module is used for: The composite AC current in the conductor under test and the estimated range of the DC current in the composite AC current are obtained based on the first electrical signal processing. The DC current in the conductor under test is obtained based on the second electrical signal; The DC current obtained from the second electrical signal is verified using the estimated range of the DC component. The verified DC current is removed from the composite AC current to obtain an AC current that does not contain DC current.

3. A non-invasive optical current transformer according to claim 1, characterized in that, The first fiber optic ring has 45 turns, and the second fiber optic ring has 75 turns.

4. A non-invasive optical current transformer according to claim 1, characterized in that, The annular housing includes a lower housing and an upper housing. The outer circumferences of the lower housing and the upper housing are connected to each other, and their inner circumferences are both connected to the baffle plate. The lower housing is connected to the bottom of the terminal box. The baffle plate is an epoxy insulating component. The first optical fiber ring is located near the lower housing, and the second optical fiber ring is located near the upper housing.

5. A non-invasive optical current transformer according to claim 4, characterized in that, The lower housing is provided with multiple protrusions, and both the mounting bracket and the protrusions are provided with through holes. Fasteners can be screwed into the through holes of the mounting bracket and the protrusions to install the annular housing on the mounting bracket. By adjusting the included angle between the annular housing and the mounting bracket, it can be adapted to the corresponding conductor to be tested.

6. A non-invasive optical current transformer according to claim 1, characterized in that, Also includes: The protective shield comprises multiple protective shield units arranged in a circumferential array on the outside of the annular shell.

7. A non-invasive optical current transformer according to claim 1, characterized in that, The terminal box includes a terminal box housing and a terminal box cover plate disposed on the terminal box housing. The pigtails of the first optical fiber ring and the second optical fiber ring are connected to the optical cable inside the terminal box housing.

8. A non-invasive optical current transformer according to claim 7, characterized in that, The terminal box housing is provided with an optical fiber tray and an optical cable pressure plate. The pigtails and optical cables of the first and second optical fiber rings are embedded in the optical fiber tray and can move with the optical cable pressure plate.

9. A non-invasive optical current transformer according to claim 7, characterized in that, The terminal box housing has an interface for cable to pass through, and the cable is fixed to the interface by a locking connector.

10. A non-invasive optical current transformer according to claim 9, characterized in that, Also includes: A corrugated pipe is fitted over the cable that passes through the interface, and the cable that passes through the connector is connected to the back-end data collector under the protection of the corrugated pipe.

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