Method and system for testing partial discharge of medium-voltage cable without metal shielding layer
By covering conductive materials at both ends of the cable and immersing them in conductive fluid to form a conductive shielding layer, the gap in the partial discharge test of medium-voltage cables without metal shielding is solved, and an effective evaluation of the insulation status and reliability of medium-voltage cables is achieved.
Patent Information
- Application Number
- CN202411683317.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-22
- Publication Date
- 2025-02-28
AI Technical Summary
The prior art has failed to effectively solve the problem of partial discharge testing of metal-free medium-voltage cables with voltage levels ranging from 1kV to 6kV, resulting in the lack of necessary insulation status and reliability assessment of cables within this voltage range.
By covering the conductive material at both ends of the cable sample to be tested, forming a conductive layer, and immersing the portion of the uncovered conductive layer into the conductive liquid to form a complete conductive shielding layer, thereby realizing the partial discharge test of the medium-voltage cable without metal shielding.
This method can effectively evaluate the insulation status and reliability of medium-voltage cables, fill the gap in the existing standards for lack of partial discharge tests for cables within this voltage range, and has low testing costs and easy material access.
Smart Images
Figure CN119535128A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of cable detection technology, and in particular to a method and system for testing partial discharge of medium-voltage cables without a metal shielding layer. Background Art
[0002] The cable partial discharge test is to evaluate the insulation status and reliability of the cable by detecting the partial discharge phenomenon in the cable insulation system. The partial discharge test can reveal defects in the insulation material, such as gaps, bubbles, impurities, etc., by detecting the partial discharge amount of the cable under high voltage. These defects will cause partial discharge when the electric field strength reaches a certain value. If not detected and handled in time, it may cause more serious insulation damage and even equipment failure.
[0003] The cable partial discharge test items and methods specified in the existing product standard GB / T12706-2020 and the test standard GB / T3048.12-2007 are mainly for cables with a voltage level greater than or equal to 6kV. Medium-voltage cables with a voltage level of 1kV to 6kV have a lower voltage, and some medium-voltage cable products do not have an outer semi-conductive layer and a metal shielding layer. Therefore, the standard does not specify partial discharge test items and describe test methods for cables in this voltage level range.
[0004] In fact, many cables with voltage levels ranging from 1kV to 6kV have special requirements for use in certain occasions and high technical requirements. In the procurement technical requirements, it is clearly stipulated that the cables need to be inspected for partial discharge tests in order to eliminate hidden defects in the cables. Therefore, it is particularly important to carry out partial discharge tests on medium voltage cables with voltage levels ranging from 1kV to 6kV. Summary of the invention
[0005] In order to implement partial discharge testing of medium voltage cables without metal shielding layers with voltage levels ranging from 1 kV to 6 kV, an embodiment of the present application provides a method and system for partial discharge testing of medium voltage cables without metal shielding layers.
[0006] On the one hand, the method includes obtaining a cable sample to be tested; coating both ends of the cable sample to be tested with conductive materials respectively, so that both ends of the cable sample to be tested are coated with at least a first target length of a conductive layer; making a cable terminal for detection based on the two ends coated with the conductive layer; immersing the cable sample to be tested in a conductive liquid, completely immersing the portion not coated with the conductive layer in the conductive liquid and ensuring that the two cable terminals extend out of the conductive liquid surface; connecting the two cable terminals to the test equipment to connect the cable sample to the test loop.
[0007] Based on the above technical solution, a conductive layer is formed by coating a conductive material on the cable sample to be tested, and the remaining part not coated with the conductive layer is immersed in a conductive liquid, so that a complete conductive shielding layer is formed outside the insulating layer of the cable sample to be tested. In this way, the partial discharge test of the cable sample to be tested can be completed based on the conductive shielding layer.
[0008] In one example, coating the two ends of the cable sample to be tested with conductive materials respectively includes overlapping and wrapping semi-conductive tapes around the two ends of the cable sample to be tested.
[0009] In one example, overlappingly wrapping the semi-conductive tape on both ends of the cable sample to be tested includes: stretching the semi-conductive tape before wrapping; wrapping the stretched semi-conductive tape continuously, completely and flatly on both ends of the cable sample to be tested in an overlapping manner; wherein the wrapping angle is greater than or equal to 30°, and the wrapping overlap rate is greater than or equal to 5%.
[0010] Based on the above technical solution, the conductive material is coated on the outer surface of the cable sample to be tested by overlapping and wrapping the semi-conductive tape, so that the formed conductive layer can be complete and fit tightly with the cable sample to be tested, thereby improving the accuracy of the test.
[0011] In one example, the conductive liquid is water.
[0012] Based on the above technical solution, the test cost is low, the materials are easy to obtain, and it will not affect the cable samples to be tested. It is especially suitable for testing large quantities (or long lengths) of cables.
[0013] In one example, the method of making a detection cable terminal based on two ends coated with a conductive layer includes: fixing oil cups at the two ends to keep the metal conductors at the two end heads exposed in the oil cups, and at least a second target length of the conductive layer at each end is located below the oil cup liquid level.
[0014] In one example, the metal conductor is obtained by removing part of the insulation layer at both ends of the cable sample to be tested.
[0015] Based on the above technical solution, it can be ensured that the cable terminal used for testing the cable sample to be tested has anti-interference capability.
[0016] In one example, the second target length is 100 mm.
[0017] Based on the above technical solution, by controlling the distance that the conductive layers at both ends of the cable sample to be tested extend into the oil surface, a better anti-interference effect can be achieved, thereby ensuring that the sensitivity of the test environment meets the requirements.
[0018] In one example, immersing the cable sample to be tested in the conductive liquid to ensure that the portion not covered with the conductive layer is completely immersed in the conductive liquid includes: at least a third target length of the conductive layer at both ends extends below the liquid surface of the conductive liquid.
[0019] Based on the above technical solution, it can be ensured that a complete and stable conductive shielding layer is formed outside the cable sample to be tested.
[0020] In one example, a voltage level of the medium voltage cable without metal shielding layer is greater than or equal to 1 kV and less than or equal to 6 kV.
[0021] In one example, the test equipment performs a partial discharge test on the cable sample to be tested based on a pulse current method.
[0022] On the other hand, an embodiment of the present application provides a partial discharge test system for a medium-voltage cable without a metal shielding layer, comprising a conductive liquid container for placing a cable sample to be tested, and the system is used to implement the above-mentioned partial discharge test method for a medium-voltage cable without a metal shielding layer. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The drawings constituting a part of the present application are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.
[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0025] Figure 1 A flow chart of a partial discharge testing method for a medium voltage cable without a metal shielding layer provided in an embodiment of the present application is shown.
[0026] Figure 2 A schematic diagram of the sample structure provided in the embodiment of the present application is shown.
[0027] Figure 3 A flow chart of a partial discharge testing method for a medium voltage cable without a metal shielding layer provided in an embodiment of the present application is shown.
[0028] Figure 4 A schematic diagram of the structure of a conductive liquid container provided in an embodiment of the present application is shown. DETAILED DESCRIPTION
[0029] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.
[0030] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more, and "first", "second" and various digital numbers are only distinguished for the convenience of description and are not used to limit the scope of the embodiments of the present application.
[0031] The features, structures or characteristics in this application may be combined in one or more embodiments in any suitable manner. In various embodiments of this application, the size of the sequence number of each process does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.
[0032] Some optional features in the embodiments of the present application may be implemented independently in some scenarios without relying on other features to solve corresponding technical problems and achieve corresponding effects. They may also be combined with other features in some scenarios as needed.
[0033] In this application, unless otherwise specified, the same or similar parts between the various embodiments can refer to each other. In the various embodiments of this application, if there is no special description and logical conflict, the terms and / or descriptions between different embodiments are consistent and can be referenced to each other, and the technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships. The implementation methods of this application do not constitute a limitation on the scope of protection of this application.
[0034] The embodiments of the present application are described in detail below with reference to the accompanying drawings.
[0035] The method provided in the embodiment of the present application can realize partial discharge testing of medium-voltage cables without metal shielding layers, thereby filling the gap in the current standard for partial discharge testing of medium-voltage cables without metal shielding layers with voltage levels of 1kV to 6kV.
[0036] The test method provided in the embodiment of the present application is implemented based on a partial discharge test system for medium-voltage cables without a metal shielding layer. The test system includes a conductive liquid container and a test device, wherein the conductive liquid container is used to place the cable sample to be tested. The test device is the test device required by the standard GB / T3048.12-2007. Both ends of the cable sample to be tested are connected to the test device to access the test circuit, and then a partial discharge test is performed on the cable sample to be tested according to the test procedure in the standard GB / T3048.12-2007.
[0037] Please refer to Figure 1 In an embodiment of the present application, a method for partial discharge testing of a medium-voltage cable without a metal shielding layer is provided. By optimizing the sample preparation steps, partial discharge testing of a medium-voltage cable without a metal shielding layer can be achieved based on the test procedure in standard GB / T3048.12-2007. The method specifically includes the following steps.
[0038] S101, obtaining a cable sample to be tested.
[0039] The cable sample to be tested is a medium voltage cable without a metal shielding layer, and the voltage level is greater than or equal to 1kV and less than or equal to 6kV.
[0040] In practice, the cable sample to be tested can be a sample at one end cut from a finished cable, or a sample of a whole bundle of cables. The specific selection can be made according to the actual application requirements of the product. For example, when the length of the installation cable is 10m, 10m of cable can be cut from the bundle of cables as the cable sample to be tested. Before the product leaves the factory or is put into use, the whole bundle of cables can also be directly used as the cable sample to be tested.
[0041] S102, respectively coating both ends of the cable sample to be tested with a conductive material, so that both ends of the cable sample to be tested are coated with a conductive layer of at least a first target length.
[0042] In one implementation, the conductive material may be a metal conductive material. Specifically, the metal conductive material may be a copper tape, an aluminum tape, a metal film, etc., which can be coated on the outside of the insulation layer of the cable to be tested and form a complete conductive shielding layer.
[0043] In another embodiment, the conductive material may be a semi-conductive material. Specifically, the semi-conductive material may be a semi-conductive tape. The semi-conductive tape may fit tightly with the surface of the insulating layer of the cable sample to avoid interference of the gap between the two with the test results.
[0044] Correspondingly, coating the two ends of the cable sample to be tested with conductive materials respectively includes overlapping and wrapping semi-conductive tapes at the two ends of the cable sample to be tested. In a specific example, the semi-conductive tape can be stretched before wrapping; and the stretched semi-conductive tape is continuously, completely and flatly wrapped around the two ends of the cable sample to be tested in an overlapping manner, so as to form a conductive layer with at least the first target length at the two ends respectively, and to ensure that the interface between the starting end and the ending end of the overlapping wrapping forms a smooth and flat circular ring. The wrapping angle is not less than 30°, and the wrapping overlap rate is not less than 5%, so as to ensure that the conductive layer formed by the wrapping is flat, continuous and gapless, and is tightly fitted and fixed to the surface of the insulating layer of the cable sample to be tested.
[0045] S103, manufacturing a detection cable terminal based on the two ends covered with the conductive layer.
[0046] In practice, before making the detection cable terminal, you need to first select the type of the detection cable terminal, which can be selected from oil-paper terminal, prefabricated simple terminal, Freon (F113) terminal, oil terminal, oil-water terminal and deionized water terminal.
[0047] In this embodiment, taking the oil terminal as an example, the method for making a cable terminal for testing includes: first removing part of the insulation layer at both ends of the cable sample to be tested to expose the metal conductor of the cable core of the cable sample to be tested, and fixing oil cups at both ends of the cable sample to be tested to keep the metal conductors at both ends exposed in the oil cups, and at least a second target length of conductive layer at each end is located below the liquid level of the oil cup.
[0048] In one implementation, the step of removing the insulating layer to expose the metal conductor of the cable core may be performed before the step of wrapping the semi-conductive tape. Thus, in the step of wrapping the semi-conductive tape, only the insulating layer at both ends needs to be wrapped to keep the metal conductor exposed.
[0049] In another embodiment, the step of removing the insulating layer may also be performed after the step of wrapping the semi-conductive tape, so as to simultaneously remove the conductive layer and the insulating layer at the two end heads.
[0050] In one example, the second target length is 100 mm, which can ensure that the conductive layer can fully contact the oil in the oil cup, thereby ensuring the stability of the test structure.
[0051] S104, immersing the cable sample to be tested into the conductive liquid, ensuring that the portion not covered with the conductive layer is completely immersed in the conductive liquid and the two cable terminals extend out of the conductive liquid surface.
[0052] In one example, by placing the middle section of the cable sample to be tested into a conductive liquid container, the portion of the middle section of the cable sample to be tested that is not covered with the conductive layer is completely immersed in the conductive liquid, and at both ends, at least a third target length of the conductive layer extends below the liquid surface of the conductive liquid, so that a complete conductive shielding structure can be formed outside the insulating layer, and the effect of simulating a conductive shielding layer outside the insulating layer is achieved. The third target length is 100 mm.
[0053] In order to improve the convenience of sample preparation, reduce testing costs, and avoid adverse effects on the structure of the cable sample to be tested, tap water or other easily available conductive liquids can be used as the conductive liquid.
[0054] At this point, the sample preparation is completed. The specific sample structure can be referred to Figure 2 .
[0055] In an embodiment of the present application, the first target length L1 is equal to the cumulative value of the second target length L2, the third target length L3, and the extension length L4 required for the test, wherein the length required for the test can be estimated according to actual test requirements.
[0056] S105, connecting the cable sample to be tested to the test loop by connecting the two cable terminals to the test equipment.
[0057] After completing step 105, a partial discharge test can be performed on the cable sample to be tested. The specific test method can refer to the standards GB / T12706.2-2020 and GB / T3048.12-2007. Specifically, a partial discharge test is performed on the cable sample to be tested based on a pulse current method.
[0058] Based on the test method provided in the embodiment of the present application, a conductive layer can be formed on the surface of the cable sample to be tested and the part not covered with the conductive layer can be immersed in tap water to simulate a conductive shielding structure outside the cable sample to be tested, thereby providing a test basis for partial discharge testing, that is, by applying a voltage between each metal conductor and the conductive shielding layer, a partial discharge test of the insulating structure can be achieved. This method is simple to operate, low in cost, and easy to obtain materials and instruments. It has good commercial value and economic effects. More importantly, it realizes partial discharge testing of medium-voltage cables without metal shielding layers, filling the gap in the industry.
[0059] The above method is further explained below with reference to specific examples.
[0060] Please refer to Figure 3 In a specific example, the partial discharge test method of a medium voltage cable without a metal shielding layer specifically includes the following steps.
[0061] S301, select a semi-conductive tape.
[0062] Specifically, a self-adhesive waterproof semi-conductive tape can be used, and the width of the tape can be selected according to the outer diameter of the cable sample to be tested.
[0063] S302, remove the isolation film from the semi-conductive self-adhesive tape or the semi-conductive tape (hereinafter referred to as the tape), stretch it by more than 200%, and wrap it continuously, completely and evenly around the two end parts of the cable sample to be tested in an overlapping manner.
[0064] During the strip wrapping process, the wrapping angle should be controlled at no less than 30°, the strips should be wrapped in overlapping patterns, and the wrapping overlap rate should be controlled at no less than 5%. The interface between the starting and ending ends of the overlapping wrapping of the strips should form a smooth, flat ring.
[0065] S303, remove insulation more than 20mm from the cable end.
[0066] This allows the metal conductor to be exposed inside the oil terminal while keeping the insulating end surface of the cut portion flat and smooth.
[0067] S304, making cable oil terminals for testing.
[0068] The oil terminal of the detection cable is completed by fixing and installing the oil cup.
[0069] S305, placing the unwrapped portion of the cable in a conductive liquid container, and injecting tap water into the container so that the unwrapped portion is completely immersed in the tap water.
[0070] The tape is wrapped around the two ends of the cable sample to be tested and forms a certain length. This length always ensures that during the partial discharge test of the cable sample to be tested, the part of the tape wrapped around the cable sample to be tested in the conductive liquid should extend to a length below the liquid level of not less than 100mm, and the part at the terminal position of the test oil extends to a length below the liquid level of the oil cup of not less than 100mm.
[0071] S306, connect the oil terminal of the detection cable to the test equipment.
[0072] The test equipment includes a high-voltage power supply, a high-voltage voltmeter, a test circuit, a discharge calibrator, a double pulse generator, etc. For details, please refer to the standard GB / T3048.12-2007.
[0073] Once the test equipment is connected, the subsequent test process can be carried out. For details, please refer to the provisions of GB / T12706.2-2020 and GB / T3048.12-2007.
[0074] Please refer to Figure 4In one example of the present application, the conductive liquid container is made of insulating material, including a base 41, a first annular member 42 and a second annular member 43, wherein the upper and lower edges of the second annular member 43 are respectively connected to the base 41 and the first annular member 42 to form the side wall of the conductive liquid container, and the second annular member 43 is a foldable structure, and the height of the side wall of the conductive liquid container can be adjusted by adjusting the folding degree of the second annular member 43. Two auxiliary fixing members 44 are connected to the upper edge of the first annular member 42 to limit the two ends of the cable sample to be tested.
[0075] In one example, the second annular member 43 includes a plurality of stacked annular airbags 431, each of which is inflated independently, and each of which has a different operating height at different inflation levels. In this way, the height of the side wall of the conductive liquid container can be adjusted by controlling the inflation amount, thereby meeting the testing requirements of cable samples to be tested of different heights.
[0076] In one example, a slot 421 of a preset length is formed on the upper edge of the first annular member 42, and one end of the auxiliary fixing member 44 is fixed in the slot 421 and can slide along the slot 421, so as to facilitate the fixing of the cable. The other end of the auxiliary fixing member 44 can be a buckle, a strap, or a clamp to limit the position of the cable to be tested.
[0077] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.
Claims
1. A method for testing partial discharge of medium voltage cables without metal shielding layer, characterized in that: The method comprises: Obtain the cable sample to be tested; Coating conductive materials at both ends of the cable sample to be tested respectively, so that both ends of the cable sample to be tested are coated with a conductive layer of at least a first target length; Making detection cable terminals based on the two ends coated with the conductive layer; Immerse the cable sample to be tested in the conductive liquid, ensuring that the portion not covered with the conductive layer is completely immersed in the conductive liquid and the two cable terminals extend out of the conductive liquid surface; The two cable terminals are connected to the test equipment to connect the cable sample to be tested into the test loop.
2. The method according to claim 1, characterized in that The step of respectively coating the two ends of the cable sample to be tested with conductive materials comprises: overlapping and wrapping the two ends of the cable sample to be tested with semi-conductive tapes.
3. The method according to claim 2, characterized in that The overlapping and wrapping of the semi-conductive tapes at both ends of the cable sample to be tested comprises: Stretching the semi-conductive tape before wrapping; The stretched semi-conductive tape is continuously, completely and evenly wrapped around the two ends of the cable sample to be tested in an overlapping wrapping manner; wherein the wrapping angle is greater than or equal to 30°, and the wrapping overlap rate is greater than or equal to 5%.
4. The method according to claim 1, characterized in that: The method of manufacturing a detection cable terminal based on two ends coated with a conductive layer comprises: The oil cups are fixedly installed at the two ends, the metal conductors at the two end heads are kept exposed in the oil cups, and at least a second target length of conductive layer is located below the liquid level of the oil cups at the two end portions.
5. The method according to claim 4, characterized in that The metal conductor is obtained by removing part of the insulation layer at both ends of the cable sample to be tested.
6. The method according to claim 4, characterized in that The second target length is 100 mm.
7. The method according to claim 1, characterized in that The step of immersing the cable sample to be tested into the conductive liquid to ensure that the portion not covered with the conductive layer is completely immersed in the conductive liquid includes: at least a third target length of the conductive layer at each end extends below the liquid level of the conductive liquid.
8. The method according to claim 1, characterized in that The voltage level of the medium-voltage cable without metal shielding layer is greater than or equal to 1 kV and less than or equal to 6 kV.
9. The method according to claim 1, characterized in that: The test equipment performs partial discharge test on the cable sample to be tested based on the pulse current method.
10. A partial discharge test system for medium voltage cables without metal shielding layer, characterized in that: The system comprises a conductive liquid container for placing a cable sample to be tested, and the system is used to implement the partial discharge test method for medium-voltage cables without metal shielding layers according to any one of claims 1 to 9.