Current transformer for monitoring unbalanced current

Abstract

The utility model discloses a current transformer for monitoring unbalanced current, and relates to the technical field of power systems. Comprising a mutual inductor body, at least one secondary coil, a first primary winding and a second primary winding are arranged in the mutual inductor body, and the two primary windings penetrate through the secondary coil with the same number of turns but opposite center penetrating directions; the head end of the first primary winding is a P1 terminal, and the tail end of the first primary winding is a C2 terminal; the head end of the second primary winding is a P2 terminal, the tail end of the second primary winding is a C1 terminal, and the C1 terminal and the C2 terminal are combined to form a P3 common terminal. Two paths of current are introduced into one current transformer at the same time, synchronous monitoring and comparison of the two paths of current values are achieved, and the monitoring process of one-time unbalanced current is greatly simplified; whether the two primary currents are in a balanced state or not can be accurately judged by accurately identifying the magnitude and the direction of the secondary current.

Description

Technical Field

[0001] The utility model relates to the technical field of power systems, in particular to a current transformer for monitoring unbalanced current. Background Art

[0002] Thermal power plants operating with series compensation technology face the risk of combined generator-grid resonance divergence. If a phase-to-phase short circuit, two-phase ground fault, or three-phase fault occurs in the series compensation line, the system will experience significant transient torque amplification, which can even damage the generator set in extreme cases.

[0003] To effectively suppress subsynchronous resonance in generators, a blocking filter is typically installed on the neutral point side of the high-voltage winding of each generator set's main transformer. The filter's core function is to block subsynchronous current generated by the system from entering the generator's stator windings, ensuring stable generator operation. However, building the supporting equipment for the blocking filter requires the use of current transformers to monitor the imbalance between the two currents and assist in fault location determination. However, existing current transformers suffer from low measurement accuracy, weak anti-interference capabilities, and a cumbersome current monitoring process. Utility Model Content

[0004] The purpose of the utility model is to provide a current transformer for unbalanced current monitoring. When one of the current paths is unbalanced due to a fault, the current transformer can identify and indicate the current path where the fault is located, providing information for timely taking protective measures.

[0005] To achieve the above-mentioned objectives, the present application proposes a current transformer for unbalanced current monitoring, comprising a transformer body, in which at least one secondary coil and a first primary winding and a second primary winding are arranged, and the two primary windings pass through the secondary coil with the same number of turns but in opposite directions; the first end of the first primary winding is the P1 terminal, and the tail end is the C2 terminal; the first end of the second primary winding is the P2 terminal, and the tail end is the C1 terminal, wherein the C1 terminal and the C2 terminal are combined to form a P3 common terminal.

[0006] In a preferred embodiment, the secondary coil includes an iron core, an inner buffer insulation layer, a secondary winding, an outer buffer insulation layer and a shielding layer. The inner buffer insulation layer is wrapped around the surface of the iron core, the enameled wire of the secondary winding is evenly wound around the inner buffer insulation layer, and the two ends of the enameled wire extend out of the secondary coil as S1 terminals and S2 terminals respectively. The outer buffer insulation layer is wrapped around the outside of the secondary winding, and the shielding layer is arranged outside the outer buffer insulation layer, which is the outermost layer of the secondary coil, and an insulating gap is left when the shielding layer is close to the roots of the S1 terminals and S2 terminals of the secondary winding.

[0007] In a preferred embodiment, the iron core is a ring structure, made of silicon steel sheet or ultra-fine crystal amorphous high magnetic permeability material, and the shielding layer is made of semi-conductive material and is grounded through a copper wire to shield the secondary coil.

[0008] In a preferred embodiment, the first primary winding includes a first copper strip, a first connecting plate, a P1 terminal, and a C2 terminal, and the second primary winding includes a second copper strip, a second connecting plate, a P2 terminal, and a C1 terminal;

[0009] The first and second copper strips are wound a specific number of times through the inner diameter of the secondary coil to form a rectangular frame. A first connecting plate connects the P1 terminal to the beginning of the first copper strip, and a second connecting plate connects the P2 terminal to the beginning of the second copper strip. The C2 terminal is welded to the end of the first copper strip, and the C1 terminal is welded to the end of the second copper strip. It should be noted that the P1 terminal of the first primary winding is synonymous with the S1 terminal of the secondary winding, and the C1 terminal of the second primary winding is synonymous with the S1 terminal of the secondary winding.

[0010] In a preferred embodiment, the first copper strip of the first primary winding and the second copper strip of the second primary winding have the same number of turns and opposite directions of passage; and each turn of the first copper strip and the second copper strip are separated by insulating material, and the first copper strip and the second copper strip are also separated by insulating material.

[0011] In a preferred embodiment, when current flows through the first primary winding and the second primary winding respectively, the directions of the two currents are opposite; if the two current values ​​are equal, the output current generated between the S1 terminal and the S2 terminal of the secondary winding is zero; if the two current values ​​are not equal, the output current is not zero, and the output direction of the current indicates which current is larger.

[0012] In a preferred embodiment, the P3 common terminal is an L-shaped copper busbar, and the C2 terminal of the first primary winding and the C1 terminal of the second primary winding are combined into one wiring terminal by countersunk screws.

[0013] In a preferred embodiment, the transformer body is cast by epoxy resin, and the gap between the secondary coil and the two primary windings is filled and fixed by the epoxy resin.

[0014] To improve the outdoor performance of the current transformer, silicone rubber sheds are installed around the transformer body and P3 common terminal. These sheds are bonded to epoxy resin and consist of raised rings spaced evenly from top to bottom. The silicone rubber sheds do not affect the unbalanced current monitoring function, so technicians can choose whether to use them based on actual site needs.

[0015] In a preferred embodiment, the through holes at the tops of the P1 terminal, the P2 terminal and the P3 common terminal expose the silicone rubber sheds, which serve as the connection terminals of the current transformer.

[0016] The above technical solution adopted by the present invention has the following advantages compared with the prior art:

[0017] 1. Stable performance and high measurement accuracy: The design of the inner insulating buffer layer outside the iron core and the outer insulating buffer layer outside the secondary winding effectively reduces the impact of external forces on the performance of the iron core and secondary winding, thereby improving the measurement accuracy of the secondary winding, thereby comprehensively improving the product performance of the current transformer.

[0018] 2. Significantly enhanced anti-interference capability: By wrapping the secondary winding with semi-conductive material to form a shielding layer and grounding the shielding layer, the anti-interference capability of the current transformer is significantly improved.

[0019] 3. The current monitoring process is simplified: by introducing two currents into one current transformer at the same time, the synchronous monitoring and comparison of the two current values ​​is realized, which greatly simplifies the monitoring process of primary unbalanced current.

[0020] 4. Assisted judgment of unbalanced current: By accurately identifying the size and direction of the secondary current, it can accurately determine whether the two primary currents are in a balanced state, and indicate which current is larger when unbalanced.

[0021] 5. Outdoor performance is greatly improved: The composite insulation design of epoxy resin and silicone rubber makes the current transformer fully adaptable to the use requirements of complex outdoor environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the secondary coil structure of the current transformer;

[0023] Figure 2 Assemble only the first primary winding structure diagram for the secondary coil;

[0024] Figure 3 Assemble only the second primary winding structure diagram for the secondary coil;

[0025] Figure 4 Schematic diagram of assembling two primary windings for the secondary coil at the same time;

[0026] Figure 5 This is the front view of the epoxy resin casting body of the current transformer;

[0027] Figure 6 This is a top view of the epoxy resin cast body of the current transformer;

[0028] Figure 7 It is the P3 common terminal of the current transformer;

[0029] Figure 8 This is a schematic diagram of the overall assembly of the current transformer structure;

[0030] Figure 9 This is the appearance diagram of the current transformer;

[0031] Among them: 100 is the secondary coil, 101 is the iron core, 102 is the inner buffer insulation layer, 103 is the secondary winding, 104 is the outer buffer insulation layer, 105 is the shielding layer, 106 is the S1 terminal, 107 is the S2 terminal, 201 is the first copper strip, 202 is the first connecting plate, 203 is the P1 terminal, 204 is the C2 terminal, 301 is the second copper strip, 302 is the second connecting plate, 303 is the P2 terminal, 304 is the C1 terminal, 400 is the P3 common terminal, 401 is the countersunk screw, 500 is epoxy resin, and 501 is the silicone rubber umbrella skirt. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0033] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "multiple" means two or more, unless otherwise clearly and specifically defined. "Several" means one or more, unless otherwise clearly and specifically defined.

[0035] In the description of this application, it should be understood that the terms "center", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply 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 a limitation on this application.

[0036] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0037] like Figure 1 As shown, the secondary coil 100 is the secondary core of the current transformer and includes an iron core 101, an inner buffer insulation layer 102, a secondary winding 103, an outer buffer insulation layer 104, and a shielding layer 105. The iron core 101 is a ring-shaped structure made of a highly magnetically permeable material such as silicon steel sheet or ultrafine amorphous crystals. The inner buffer insulation layer 102 is wrapped around its surface to increase the buffer thickness, reduce the impact of external forces on the performance of the iron core 101, and insulate the iron core 101. Enameled wire is evenly wound around the outer surface of the inner buffer insulation layer 102. This layer of enameled wire forms the secondary winding 103. The surface of the enameled wire has an insulating varnish layer, providing insulation between each turn. Each layer of enameled wire is separated by insulating material. This uniform winding ensures a uniform magnetic field distribution within the secondary coil 100.

[0038] The enameled wire of the secondary winding 103 extends outside the secondary coil 100 at both ends, with one end serving as the S1 terminal 106 and the other as the S2 terminal 107. An outer buffer insulation layer 104 is wrapped around the surface of the secondary winding 103, further reducing the impact of external forces on the performance of the core 101 and secondary winding 103, thereby improving the measurement accuracy of the secondary coil 100. The outermost layer of the secondary coil 100 is a shielding layer 105 made of a semi-conductive material. When grounded, it completely shields the secondary coil 100, improving its anti-interference capabilities.

[0039] It should be noted that a gap should be left when the shielding layer 105 is close to the roots of the S1 terminal 106 and the S2 terminal 107 and should not touch them, so as to avoid a short circuit between the shielding layer 105 and the S1 terminal 106 and the S2 terminal 107.

[0040] In addition, it should be noted that only one secondary coil 100 is described in the embodiment of the present invention. In actual applications, two, three or more secondary coils 100 may be used, which all fall within the scope of the description of the present invention.

[0041] like Figure 2As shown, the first primary winding includes a first copper strip 201, a first connecting plate 202, a P1 terminal 203, and a C2 terminal 204. The P1 terminal 203 is a copper busbar with a through-hole machined on the top to serve as the transformer's terminal block, and its bottom is welded to the first connecting plate 202. The first connecting plate 202 is a C-shaped bent copper busbar, with its top welded to the P1 terminal 203 and its bottom welded to the beginning of the first copper strip 201.

[0042] The first copper strip 201 is a single piece of copper strip. The end surface of the secondary coil 100 near the S1 terminal 106 is used as a reference surface. The first copper strip 201 is inserted from this reference surface into the inner diameter of the secondary coil 100, then loops around the outer diameter to form a square shape and is inserted back into the inner diameter of the secondary coil 100. Each time the first copper strip 201 passes through the inner diameter of the secondary coil 100 is considered a turn. The end of the first copper strip 201 is welded to the C2 terminal 204. The C2 terminal 204 is a copper busbar with a threaded hole machined on the top plane and the bottom welded to the end of the first copper strip 201.

[0043] It should be noted that each turn of the first copper tape 201 needs to be separated by insulating material and cannot touch each other. For example, the first turn and the second turn are insulated, and the second turn and the third turn are insulated. In addition, except for the starting end of the first copper tape 201 being welded to the first connecting plate 202, the remaining second and third turns of the first copper tape 201 and the first connecting plate 202 also need to be separated by insulating material to avoid short circuits between each other.

[0044] In addition, it should be noted that the number of turns of the first copper strip 201 in the above description and drawings is three turns, which is only a number set for demonstration. In actual application, it can be other turns, and other turns are also within the scope of the description of the present invention.

[0045] like Figure 2 As shown, if the P1 terminal 203 is used as the input terminal of the primary current and the C2 terminal 204 is used as the output terminal of the primary current, the secondary coil 100 will induce and output the secondary current, and at this time the S1 terminal 106 and the P1 terminal 203 are the same-named terminals.

[0046] like Figure 3 As shown, the second primary winding includes a second copper strip 301, a second connecting plate 302, a P2 terminal 303, and a C1 terminal 304. The P2 terminal 303 is a copper busbar with a through-hole machined on the top to serve as the transformer's terminal block, and its bottom is welded to the second connecting plate 302. The second connecting plate 302 is a C-shaped bent copper busbar, with its top welded to the P2 terminal 303 and its bottom welded to the beginning of the second copper strip 301.

[0047] The second copper strip 301 is a single piece of copper strip. Using the end surface of the secondary coil 100 near the S1 terminal 106 as the reference surface, the second copper strip 301 is inserted into the inner diameter of the secondary coil 100 from the direction opposite to this reference surface. It then wraps around the outer diameter to form a square shape and is inserted back into the inner diameter of the secondary coil 100. Each time the second copper strip 301 passes through the inner diameter of the secondary coil 100, it constitutes a turn. The end of the second copper strip 301 is welded to the C1 terminal 304. The C1 terminal 304 is a copper bar with a threaded hole machined on the top surface. The bottom is welded to the end of the second copper strip 301.

[0048] It should be noted that each turn of the second copper tape 301 needs to be separated by insulating material and cannot touch each other. For example, the first turn and the second turn are insulated, and the second turn and the third turn are insulated. Except for the starting end of the second copper tape 301 being welded to the second connecting plate 302, the remaining second and third turns of the second copper tape 301 and the second connecting plate 302 also need to be separated by insulating material to avoid short circuits between each other.

[0049] In addition, it should be noted that the number of turns of the second copper strip 301 in the above description and drawings is three turns, which is only a number set for demonstration. In actual application, it can be other turns, and other turns are also within the scope of the description of the present invention.

[0050] like Figure 3 As shown, if the P2 terminal 303 is used as the input terminal of the primary current and the C1 terminal 304 is used as the output terminal of the primary current, the secondary coil 100 will induce and output the secondary current, and at this time the S2 terminal 107 and the P2 terminal 303 are the same-named terminals.

[0051] It should be noted that the first copper strip 201 of the first primary winding and the second copper strip 301 of the second primary winding have the same number of turns through the core, and the directions in which they pass through the secondary winding 100 are opposite.

[0052] like Figure 4 As shown, the first primary winding and the second primary winding are assembled on the secondary coil 100 at the same time, the two windings are placed side by side, and a distance is maintained between the first primary winding and the second primary winding.

[0053] It should be noted that Figure 4 After the middle structure is assembled, it needs to be installed in the casting mold and poured with epoxy resin 500. After the epoxy resin 500 is cured, it can be Figure 4 Each structure in the middle is fixed.

[0054] like Figure 5 、 Figure 6As shown, the gap between the first primary winding and the second primary winding is filled with epoxy resin 500, and the gap between the secondary coil 100 and the first copper strip 201 and the second copper strip 301 is also filled with epoxy resin 500. The epoxy resin serves to insulate and fix the various structures.

[0055] like Figure 7 As shown, the P3 common terminal 400 is an L-shaped copper busbar. A through hole is machined on the top of the P3 common terminal 400 and used as a terminal block for the transformer. The bottom is a flat surface with countersunk screw holes machined above the flat surface.

[0056] like Figure 8 As shown, in Figure 5 、 Figure 6 Install P3 common terminal 400 on the basis of the . In order to make the structure clear, Figure 8 Epoxy resin 500 is hidden in the P3 common terminal 400. Place P3 common terminal 400 on top of C2 terminal 204 and C1 terminal 304, with the bottom surface of P3 common terminal 400 in contact with the top surfaces of C2 terminal 204 and C1 terminal 304. Screw countersunk screw 401 passes through the countersunk screw hole on P3 common terminal 400 and is screwed into the threaded holes on the top of C2 terminal 204 and C1 terminal 304. P3 common terminal 400 combines C2 terminal 204 and C1 terminal 304 into a single terminal block.

[0057] Connecting the current transformer of the present invention to the power grid involves first connecting the input of the first current path to the P1 terminal 203, and the output of the first current path to the P3 terminal 400. Next, the input of the second current path is connected to the P2 terminal 303, and its output is similarly connected to the P3 terminal 400. When current flows through the first and second copper strips 201 and 301, they each independently generate a specific electric field. Crucially, because the currents in the first and second copper strips 201 and 301 flow in opposite directions, the electric fields they generate in the secondary coil 100 cancel each other out.

[0058] When the first current value is equal to the second current value, the electric fields cancel each other out to form a neutralization effect. Under this condition, the output current between the S1 terminal 106 and the S2 terminal 107 of the secondary winding 103 will be zero.

[0059] When the first current is greater than the second current, the electric field of the first current is partially offset by the electric field of the second current, and the weakened electric field appears as the electric field of the first current. Under this condition, the output current between the S1 terminal 106 and the S2 terminal 107 of the secondary winding 103 will be positive.

[0060] When the first current is smaller than the second current, the electric field of the second current is partially offset by the electric field of the first current, and the weakened electric field appears as the electric field of the second current. Under this condition, the output current between the S1 terminal 106 and the S2 terminal 107 of the secondary winding 103 will be negative.

[0061] With this arrangement, by detecting the output currents of the secondary end S1 terminal 106 and the S2 terminal 107 , it is possible to determine whether the first current and the second current of the primary end are balanced. If unbalanced, which current is larger, the first current or the second current?

[0062] like Figure 9 As shown, in Figure 8 On this basis, a silicone rubber shed 501 is applied to the entire current transformer's epoxy resin 500 and the P3 common terminal 400. Silicone rubber adhesive is applied to the epoxy resin 500 to bond the silicone rubber shed 501 to the epoxy resin 500 as a single unit. Silicone rubber shed 501 serves as the current transformer's external insulation. The silicone rubber shed 501 comprises raised rings spaced parallel and evenly spaced from top to bottom, effectively increasing the product's surface creepage distance, improving its pollution flashover resistance in outdoor conditions, and enabling operation at higher altitudes.

[0063] It should be noted that the through holes at the tops of the P1 terminal 203 , the P2 terminal 303 , and the P3 common terminal 400 all need to expose the outer silicone rubber shed 501 to serve as the connection terminals of the current transformer.

[0064] Furthermore, it should be noted that the silicone rubber sheds 501 are a special design for outdoor use of the current transformer. Whether or not the silicone rubber sheds 501 are present does not affect the current transformer's ability to monitor unbalanced current. Therefore, current transformers without the silicone rubber sheds 501 are also within the scope of protection of this invention.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A current transformer for unbalanced current monitoring, comprising a transformer body, characterized in that: At least one secondary coil and a first primary winding and a second primary winding are arranged in the transformer body. The two primary windings pass through the secondary coil with the same number of turns but in opposite directions. The first end of the first primary winding is the P1 terminal and the tail end is the C2 terminal. The first end of the second primary winding is the P2 terminal and the tail end is the C1 terminal, where the C1 terminal and the C2 terminal are combined to form a P3 common terminal.

2. A current transformer for unbalanced current monitoring according to claim 1, characterized in that: The secondary coil includes an iron core, an inner buffer insulation layer, a secondary winding, an outer buffer insulation layer and a shielding layer. The inner buffer insulation layer is wrapped around the surface of the iron core. The enameled wire of the secondary winding is evenly wound around the inner buffer insulation layer, and the two ends of the enameled wire extend out of the secondary coil as S1 terminals and S2 terminals respectively. The outer buffer insulation layer is wrapped around the outside of the secondary winding. The shielding layer is arranged outside the outer buffer insulation layer, which is the outermost layer of the secondary coil, and an insulation gap is left when the shielding layer is close to the roots of the S1 terminals and S2 terminals of the secondary winding.

3. The current transformer for unbalanced current monitoring according to claim 2, characterized in that: The iron core is a ring-shaped structure and is made of silicon steel sheets or ultra-fine crystal amorphous high-magnetic permeability materials. The shielding layer is made of semi-conductive materials and is grounded to shield the secondary coil.

4. The current transformer for unbalanced current monitoring according to claim 1, characterized in that: The first primary winding includes a first copper strip, a first connecting plate, a P1 terminal, and a C2 terminal, and the second primary winding includes a second copper strip, a second connecting plate, a P2 terminal, and a C1 terminal; The first copper strip and the second copper strip pass through the inner diameter of the secondary coil with a specific number of turns to form a square shape; the first connecting plate connects the P1 terminal to the starting end of the first copper strip, and the second connecting plate connects the P2 terminal to the starting end of the second copper strip; the C2 terminal is welded to the end of the first copper strip, and the C1 terminal is welded to the end of the second copper strip.

5. The current transformer for unbalanced current monitoring according to claim 4, characterized in that: The first copper strip of the first primary winding and the second copper strip of the second primary winding have the same number of turns and opposite directions of passage; and each turn of the first copper strip and the second copper strip are separated by insulating material, and the first copper strip and the second copper strip are also separated by insulating material.

6. The current transformer for unbalanced current monitoring according to claim 1, characterized in that: When current flows through the first primary winding and the second primary winding respectively, the directions of the two currents are opposite; if the two current values ​​are equal, the output current generated between the S1 terminal and the S2 terminal of the secondary winding is zero; if the two current values ​​are not equal, the output current is not zero, and the output direction of the current indicates which current is larger.

7. The current transformer for unbalanced current monitoring according to claim 1, characterized in that: The P3 common terminal is an L-shaped copper busbar, and the C2 terminal of the first primary winding and the C1 terminal of the second primary winding are combined into one wiring terminal by countersunk screws.

8. The current transformer for unbalanced current monitoring according to claim 1, characterized in that: The transformer body is cast by epoxy resin, and the gap between the secondary coil and the two primary windings is filled and fixed by the epoxy resin.

9. The current transformer for unbalanced current monitoring according to claim 1, characterized in that: The transformer body and the outer periphery of the P3 common terminal are provided with a silicone rubber shed, and the silicone rubber shed includes convex rings that are distributed in parallel and at equal intervals from top to bottom.

10. The current transformer for unbalanced current monitoring according to claim 1, characterized in that: The through holes at the top of the P1 terminal, the P2 terminal and the P3 common terminal expose the silicone rubber sheds, which serve as the connection terminals of the current transformer.

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