Mould for preparing electric tree sample for resin degradation test and test method

Abstract

The invention provides a mold for preparing an electric tree sample for a resin degradation test and a test method. By designing a curing grinding tool and a sample preparation method, control over experimental interference factors such as a needle electrode direction-fiber direction included angle, the number of fibers and a needle-fiber linear distance is achieved, and the interface performance serves as a unique variable; a needle-plate electrode system with specific fiber and resin matrix types and fiber / resin matrix interface states is prepared, and internal defects of fiber reinforced resin materials in different interface composition structures and interface states can be simulated; a brand-new method is provided for observing the electrical tree degradation condition of the fiber-reinforced epoxy composite material influenced by the interface performance and researching the insulation failure mechanism of the composite material; by adopting fibers and matrixes made of different materials, fibers with different diameters and the like, regulation and control on an interface composition structure can be realized; the interface state can be regulated and controlled by prefabricating different interface defects, pretreating fibers by adopting different modification methods and the like.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage equipment insulation, and in particular to a mold and an experimental method for preparing an electrical tree specimen using a fiber-reinforced resin. Background Art

[0002] In the power system, the insulation performance of high-voltage equipment is one of the key factors to ensure the safe and stable operation of the power grid. With the further increase of transmission voltage level and transmission capacity, the insulation problem of high-voltage equipment has become increasingly prominent, especially the electrical treeing phenomenon, which has a significant impact on the reliability and service life of insulation materials.

[0003] In recent years, fiber-reinforced resin composites have been widely used in the field of high-voltage equipment insulation due to their excellent mechanical and insulation properties. However, under the influence of electric fields and external environments, the insulation properties of fiber-reinforced resin composites may gradually decline, among which electrical tree degradation is one of the main causes of insulation failure, posing a threat to the safe and stable operation of power systems.

[0004] Electrical tree degradation is a discharge phenomenon caused by the insulation material under the action of an electric field. When there are defects inside the insulation material or it is affected by external factors (such as temperature, humidity, mechanical stress, etc.), the electric field strength may be concentrated in these areas, resulting in partial discharge. These discharge channels gradually expand in the material, forming a dendrite structure, which eventually leads to a decrease in the insulation performance of the material or even failure.

[0005] Fiber-reinforced resin composites are composed of resin matrix and fiber reinforcement. The resin matrix provides the material with adhesion and basic insulation properties, while the fiber reinforcement provides high strength and high modulus, giving the material better mechanical properties and aging resistance. The interfacial bonding of the fiber / matrix has an important influence on the electrical tree degradation phenomenon of the composite material. When there are defects in the interface, insulation degradation tends to develop rapidly along the interface, exacerbating the insulation failure of the composite material.

[0006] Therefore, conducting research on the electrical tree degradation experimental method of fiber reinforced resin interface performance is of great significance for improving the insulation performance of high-voltage equipment and ensuring the safety of power systems. In order to evaluate the electrical tree degradation performance, specific experimental methods are required. These methods usually include steps such as preparing samples, applying electric fields, observing and recording discharge phenomena. Among them, sample preparation is one of the key links, and it is necessary to ensure that the size, shape and internal structure of the sample meet the experimental requirements. At present, there is still a lack of electrical tree degradation experimental methods that can effectively evaluate the interface performance of fiber reinforced resins.

[0007] The bottleneck problem of current technology lies in the preparation of electrical tree specimens of composite materials. Ordinary fiber / resin matrix composite samples are difficult to meet the requirements of electrical tree degradation experiments. The main reasons are: 1. There are many influencing factors in the experiment, and it is impossible to eliminate the interference of other experimental variables. General composite samples contain a large number of fiber / resin matrix interfaces. Factors such as fiber and resin types, fiber volume content and their arrangement near the needle tip will affect the results of the electrical tree experiment, resulting in the experimental method being unable to directly evaluate the interface performance. 2. The observation of experimental phenomena is difficult. In the electrical tree experiment, a stereo microscope is generally used to achieve real-time observation of the growth process of the electrical tree. However, due to the obstruction of a large number of fibers inside the composite material (especially opaque fibers, such as aramid, etc.), the morphology of the electrical tree is not easy to observe. Summary of the invention

[0008] In view of this, on one hand, the present invention proposes a mold for preparing electric tree specimens for resin degradation test, including a mold body, the mold body is provided with a resin dipping tank and a fiber tank and a needle electrode tank which penetrate the mold body laterally and are connected to the resin dipping tank, the resin dipping tank divides the top surface of the mold body into a first side surface and a second side surface, the limiting tank is arranged through the first side surface and the second side surface, the needle electrode tank is arranged through the first side surface, and the width of the first side surface is greater than the width of the second side surface, the fiber tank is used for placing fibers, and the needle electrode tank is used for placing high-voltage needle electrodes, and the side wall of the resin dipping tank facing the first longitudinal end of the mold body is at an obtuse angle with the bottom of the resin dipping tank, forming an inclined surface structure.

[0009] Furthermore, the fiber slot and the needle electrode slot are combined into a first pair of slots extending through the first side surface and the second side surface, and the fiber and the high-voltage needle electrode are placed in the first pair of slots, forming a position setting form for the fiber and the high-voltage needle electrode.

[0010] Preferably, the width of the first pair of notches matches the width of the high-voltage needle electrode, so as to facilitate fixing of the high-voltage needle electrode.

[0011] Furthermore, the first pair of notches includes two notches, one is arranged on the first side, and the other is arranged on the second side, the fiber is placed in the two notches, and the high-voltage needle electrode is placed in the notch on the first side, so that the fixation of the high-voltage needle electrode is more stable.

[0012] Preferably, the two notches are equidistant from the side wall of the dipping tank toward the second longitudinal end of the mold body.

[0013] Furthermore, the fiber groove is a second pair of grooves arranged to pass through the first side surface and the second side surface, and the needle electrode groove is a third pair of grooves arranged to pass through the first side surface. When the fiber is placed in the second pair of grooves, it can pass through the first side surface and the second side surface. When the high-voltage needle electrode is placed in the third pair of grooves, it is placed at the position of the first side surface. The second pair of grooves and the third pair of grooves are provided to provide another setting form for the position setting of the fiber and the high-voltage needle electrode.

[0014] Furthermore, the width of the second pair of notches matches the width of the high-voltage needle electrode.

[0015] The present invention provides a mold for preparing an electrical tree specimen for a resin degradation test, which has the following advantages: the angle between the bottom of the resin dipping tank of the mold and one of its sides is an obtuse angle, which is convenient for demoulding the sample; by designing a curing mold, the control of experimental interference factors such as the needle electrode direction-fiber direction angle, the number of fibers and the needle-fiber straight-line distance is achieved, so that the interface performance is used as the only variable; a needle-plate electrode system with specific fiber, resin matrix type and fiber / resin matrix interface state is prepared, which can simulate the internal defects of fiber-reinforced resin materials under different interface composition structures and interface states, and provides a brand-new mold for observing the electrical tree degradation of fiber-reinforced epoxy composite materials affected by interface performance and studying the insulation failure mechanism of composite materials.

[0016] Another aspect of the present invention provides an electrical tree specimen for resin degradation test, which is prepared by using any of the above-mentioned molds.

[0017] The third aspect of the present invention also provides a method for testing degradation of electrical tree specimens, which uses the above-mentioned electrical resin sample for testing, including: Prepare electrical tree specimens of different shapes, and use a plurality of the molds to prepare a plurality of electrical tree specimens whose internal fibers and high-voltage needle electrode arrangements meet the experimental requirements; Observe the growth morphology of electrical dendrites, observe the development process of electrical dendrites with a microscope, and record the morphological graphs; Select node graphs for analysis, select multiple time node graphs for analysis, and select breakdown time graphs for analysis.

[0018] Furthermore, the method for preparing the electrical tree specimen includes: Place the fiber in the limiting groove. After controlling the position, stick the two ends of the outer side of the fiber to the outer side of the mold body to fix the fiber position. Place the high-voltage needle electrode, clean the pre-polished high-voltage needle electrode to remove impurities, place it in the needle electrode groove, and then seal the limit groove and the needle electrode groove; Prepare the sample, pour the prepared resin into the dipping tank with the fiber and the electrode, complete the resin curing according to the designed curing process, and prepare the sample for the electrical tree degradation experiment; Grind the sample, grind the bottom of the sample, control the needle-plate distance to meet the preset requirements, ensure good contact between the sample and the ground electrode, and stick copper foil on the bottom of the sample, which is connected to the ground electrode.

[0019] Furthermore, when sealing the limiting groove and the needle electrode groove, silicone rubber or other materials are used for sealing.

[0020] Furthermore, the prepared electrical trees include electrical trees with single fiber and single interface and electrical trees with double fibers and double interfaces.

[0021] Furthermore, the length of the fiber is longer than the length of the mold body.

[0022] Furthermore, it is characterized in that the high-voltage needle electrode is polished to control the needle tip curvature diameter to be 5±1 μm, or to reach a designed diameter range.

[0023] Furthermore, the straight-line distance between the high-voltage needle electrode and the fiber is ≤300 μm.

[0024] Furthermore, the fiber is any one of aramid fiber, glass fiber, and polyester fiber, and the fiber is in the form of any one of fiber filament, fiber bundle, and fiber cloth.

[0025] Preferably, when the fiber is in the form of fiber filaments, the number of the fiber filaments is single or double.

[0026] Preferably, when the number of the fiber filaments is two, two fibers are set as the experimental group and the control group respectively.

[0027] Furthermore, when cleaning the high-voltage needle electrode, the polished needle electrode is placed in an ethanol solution and ultrasonically cleaned for 30 minutes, or other cleaning procedures are used to remove impurities.

[0028] Furthermore, when polishing the sample, the needle-plate distance is controlled to be 1±0.1 mm, or to reach a designed distance range, while ensuring good contact between the sample and the ground electrode.

[0029] Furthermore, a copper foil is pasted on the bottom of the sample. The thickness of the copper foil is 100 μm, and the copper foil is connected to the ground electrode.

[0030] The present invention provides a method for testing degradation of electrical tree specimens, which has the following advantages: by designing a curing mold and a sample preparation method, experimental interference factors such as the angle between the needle electrode direction and the fiber direction, the number of fibers and the needle-fiber straight-line distance can be controlled, so that the interface performance is used as the only variable; a needle-plate electrode system with specific fiber, resin matrix type and fiber / resin matrix interface state is prepared, which can simulate different interface composition structures and internal defects of fiber-reinforced resin materials under interface states, and provides a new method for observing the electrical tree degradation of fiber-reinforced epoxy composite materials affected by interface performance and studying the insulation failure mechanism of composite materials; by using fibers and matrices of different materials, fibers of different diameters, etc., the interface composition structure can be regulated; by prefabricating different interface defects, using different modification methods to pretreat the fibers, etc., the interface state can be regulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings: Figure 1 A schematic diagram of the overall structure of a mold for preparing an electrical tree specimen provided by an embodiment of the present invention; Figure 2 A sample diagram of a fiber bundle provided by an embodiment of the present invention; Figure 3 A sample diagram of a fiber filament when the fiber morphology provided in the embodiment of the present invention is a fiber filament; Figure 4 A sample diagram of two fiber filaments when the fiber morphology provided in the embodiment of the present invention is a fiber filament; Figure 5 A sample image of the prepared electrical tree specimen after polishing provided in an embodiment of the present invention; Figure 6 A schematic diagram of the electrical tree morphology of a single fiber sample in group A after breakdown provided by an embodiment of the present invention; Figure 7 A schematic diagram of the electrical tree morphology of a single fiber sample of group B after breakdown provided by an embodiment of the present invention; Figure 8 The schematic diagram of the electrical tree development process of the single fiber sample of group B provided in the embodiment of the present invention is as follows: 8-1, 0min; 8-2, 10min; 8-3, breakdown; Fig. 9 A schematic diagram of electrical tree morphology of dual-fiber samples with different interface properties provided by an embodiment of the present invention; Fig.10A degradation test method for an electrical tree specimen prepared from a fiber-reinforced resin provided in an embodiment of the present invention; In the figure, 1. mold body, 2. glue dipping tank, 3. first pair of notches, 4. high-voltage needle electrode, 5. fiber; 11. first side surface, 12. second side surface, 21. inclined surface structure. DETAILED DESCRIPTION

[0032] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] See also Figure 1 As shown, it is a mold for preparing an electrical tree specimen for a resin degradation test provided by an embodiment of the present invention, comprising a mold body 1, wherein the mold body 1 is provided with a resin dipping tank 2 and a fiber tank and a needle electrode tank that penetrate the mold body 1 in the transverse direction and are connected to the resin dipping tank 2. In this embodiment, the fiber tank and the needle electrode tank are combined into a first pair of notches 3, and the resin dipping tank 2 separates the top surface of the mold body 1 into a first side surface 11 and a second side surface 12, and the width of the first side surface 11 is greater than the width of the second side surface 12. The first pair of notches 3 are arranged through the first side surface 11 and the second side surface 12. When the fiber 5 is placed, it penetrates the two notches of the first pair of notches 3 as the fiber tank to carry the fiber. When the high-voltage needle electrode 4 is placed, it is placed at the notch position of the first side surface 11 as the needle electrode tank to carry the high-voltage needle electrode. The side wall of the resin dipping tank 2 facing the first longitudinal end of the mold body 1 is at an obtuse angle with the bottom of the tank of the resin dipping tank, forming an inclined surface structure 21, and the electrical resin specimen prepared by using the mold is easier to demold.

[0034] In this embodiment, the width of the first pair of notches 3 matches the width of the high-voltage needle electrode 4 , which also means that the width of the fiber groove and the needle electrode groove matches the width of the high-voltage needle electrode 4 , which facilitates fixing the high-voltage needle electrode 4 .

[0035] In this embodiment, the first pair of notches 3 includes two notches, one is arranged on the first side 11, and the other is arranged on the second side 12. The fiber 5 is placed in the two notches, and the high-voltage needle electrode 4 is placed in the notch of the first side 11. Since the first side 11 has a larger width, it provides a better bearing surface for the placement of the high-voltage needle electrode 4, which facilitates stable placement.

[0036] In this embodiment, the distances between the two notches and the side wall of the dipping tank 2 toward the second longitudinal end of the mold body 1 are equal.

[0037] In another embodiment of the present invention, the fiber slot is a second pair of slots set through the first side and the second side, the needle electrode slot is a third pair of slots set through the first side, and the second pair of slots and the third pair of slots are arranged in parallel. When the fiber is placed in the second pair of slots, it can pass through the first side and the second side. When the high-voltage needle electrode is placed in the third pair of slots, it is placed at the position of the first side. By setting the fiber slot and the needle electrode slot as two pairs of slots arranged in parallel, more implementation methods are provided for the placement position and angle of the fiber and the high-voltage needle electrode. The width of the second pair of slots matches the width of the high-voltage needle electrode, and the width of the third pair of slots can also match the width of the high-voltage needle electrode, so that the positions of the fiber slot and the needle electrode slot can be interchanged, providing a new setting method for the placement of the high-voltage needle electrode and the fiber. The electrical resin sample prepared by the mold can form different discharge positions in the discharge laboratory, providing different presentation forms for the degradation of electrical dendrites.

[0038] A mold for preparing an electrical tree specimen for a resin degradation test disclosed in an embodiment of the present invention has the following beneficial technical effects: the angle between the bottom of the resin dipping tank of the mold and one of its sides is an obtuse angle, which is convenient for demolding the sample; by designing a curing mold, experimental interference factors such as the needle electrode direction-fiber direction angle, the number of fibers and the needle-fiber straight-line distance are controlled, so that the interface performance is used as the only variable; a needle-plate electrode system for preparing specific fibers, resin matrix types and fiber / resin matrix interface states can simulate the internal defects of fiber-reinforced resin materials under different interface composition structures and interface states, providing a new mold for observing the electrical tree degradation of fiber-reinforced epoxy composites affected by interface performance and studying the insulation failure mechanism of composite materials.

[0039] The present invention also discloses a method for testing degradation of an electrical tree specimen, comprising the following steps: S01, preparing electric tree specimens of different shapes, using multiple molds of different specifications to prepare multiple electric tree specimens whose internal fibers and high-voltage needle electrode arrangements meet the experimental requirements. Specifically, the molds used can produce a variety of electric tree specimens with high-voltage needle electrodes and fibers at different positions and angles. Since the molds limit the positions of the high-voltage needle electrodes and fibers, the experimental interference factors such as the angle between the needle electrode direction and the fiber direction, the number of fibers, and the needle-fiber straight-line distance can be controlled, making the interface performance the only variable; S02, observe the growth morphology of electrical dendrites, observe the development process of electrical dendrites with a microscope, and record the morphological graphs. The morphology of electrical dendrites can be observed intuitively through the complete graphs; S03, selecting node graphs for analysis, selecting multiple time node graphs for analysis, and selecting breakdown graphs for analysis, so as to better understand the degradation process of electrical tree branches and evaluate the resin interface performance.

[0040] In this embodiment, the method for preparing electrical tree specimens of multiple forms includes the following steps: SO11, place the fiber, place the fiber in the fiber slot 3, control the position, and stick the outer ends of the fiber to the outer side of the mold body to fix the fiber position; S012, placing the high-voltage needle electrode, cleaning the pre-polished high-voltage needle electrode to remove impurities, placing it in the needle electrode groove, and then sealing the needle electrode groove and the fiber groove; S013, preparing a sample, pouring the prepared resin into a resin dipping tank containing fibers and electrodes, and completing the resin curing according to the designed curing process to prepare a sample for the electrical tree degradation test; S014, polish the sample, polish the bottom of the sample, control the needle-plate distance to meet the preset requirements, ensure good contact between the sample and the ground electrode, and stick copper foil on the bottom of the sample, which is connected to the ground electrode.

[0041] In this embodiment, silicone rubber or other materials are used to seal the fiber groove and the needle electrode groove.

[0042] In this embodiment, the prepared electrical trees include electrical trees with single fiber and single interface and electrical trees with double fibers and double interfaces.

[0043] In a specific operation, the length of the fiber is longer than the length of the mold body.

[0044] In this embodiment, the high-voltage needle electrode is polished to control the tip curvature diameter to be 5±1 μm, or to reach a designed diameter range. It should be understood that the tip curvature refers to the tip curvature of the high-voltage needle.

[0045] Meanwhile, the straight-line distance between the high-voltage needle electrode and the fiber is ≤300 μm.

[0046] In this embodiment, in preparing the electrical resin sample, the fiber used is any one of aramid fiber, glass fiber, and polyester fiber, and the fiber is in the form of any one of fiber filament, fiber bundle, and fiber cloth.

[0047] In this embodiment, when the fiber is in the form of fiber filaments, the number of the fiber filaments is single or double.

[0048] When the number of the fiber filaments is two, two fibers are set as the experimental group and the control group respectively.

[0049] In specific operations, when cleaning the high-voltage needle electrode, place the polished needle electrode in an ethanol solution and perform ultrasonic cleaning for 30 minutes, or use other cleaning procedures to remove impurities.

[0050] In this embodiment, when polishing the sample, the needle-plate distance is controlled to be 1±0.1mm, or to reach the designed distance range, while ensuring good contact between the sample and the ground electrode. It should be understood that the needle-plate distance refers to the distance between the high-voltage needle electrode and the ground electrode at the bottom of the electric tree sample. Copper foil is pasted on the bottom of the sample, the thickness of the copper foil is 100μm, and the copper foil is connected to the ground electrode.

[0051] In the following, in combination with specific embodiments, a degradation test method is performed on an electrical resin sample prepared by using the mold disclosed in the embodiment of the present invention to prepare a fiber-reinforced resin electrical tree sample, and the performance of the sample is tested.

[0052] The fibers used in this embodiment are aramid fibers.

[0053] Before preparing the sample, the aramid fiber was pretreated to achieve the control of the sample interface state. The aramid fiber was divided into two groups: A, B, and C. Group A was not treated, group B was treated with vacuum drying and dehumidification at 100°C for 30 minutes in an oven, and group C was treated with DBD plasma modification in air atmosphere for 30 seconds after vacuum drying and dehumidification at 100°C for 30 minutes, with a plasma discharge power of 73W.

[0054] By designing the curing mold and sample preparation method, the direction of the high-voltage needle electrode is controlled to be parallel to the direction of the fiber. The straight-line distance between the needle and the fiber is about 280μm, that is, the shortest distance between the high-voltage needle tip and the fiber. By changing the position and width of the needle electrode groove and the fiber groove, the straight-line distance between the needle and the fiber and the angle between the needle electrode direction and the fiber direction can be controlled. In order to ensure that the electrical dendrites grow to the interface, it is recommended that the straight-line distance between the needle and the fiber does not exceed 300μm. The mold used in this experiment is as follows: Figure 1As shown, the mold includes a rectangular mold body and a first pair of notches 1 provided thereon, which are used as fiber slots and needle electrode slots; a dip-resin tank is provided in the mold body, and the size of the electric tree specimen prepared by using the dip-resin tank is: 5 mm thick, 15 mm wide, and 20 mm long. The dip-resin tank 2 separates the top surface of the mold body 1 into a first side surface 11 and a second side surface 12, and the thickness of the first side surface 11 is greater than the thickness of the second side surface 12. The width of the two notches of the first pair of notches is 400 μm and the depth is 3 mm. It can be used as a needle electrode slot and a fiber slot at the same time, and is used to place the fiber and the high-voltage needle electrode at the same time, so that the fiber 5 passes through the first pair of notches (that is, the fiber slot 3) and the dip-resin tank 2. The high-voltage needle electrode 4 is placed in the notch of the first side surface 11, and its needle electrode diameter is 400 μm, which matches the width of the two notches. The bottom and side walls of the dip-resin tank 2 form a slope structure 21, which is convenient for demolding the electric tree specimen prepared therein. In addition, in specific applications, a preparation mold containing more notches can also be selected to allow the fiber and the high-voltage needle electrode to be placed separately. The different positional relationships between the two can form different discharge positions when the electrical resin sample is discharged, providing different presentation forms for the degradation of electrical trees.

[0055] The single fiber samples were prepared using the fiber filaments of group A and group B, that is, only one fiber was placed in each sample.

[0056] The double fiber samples were prepared by using fiber filaments of group A and group C. That is, one fiber filament of group A and one fiber filament of group C were placed in each sample at the same time. The placement positions were respectively the two corners of the lower edge of the needle electrode groove. Thus, the comparative observation of the experimental phenomena under two different interface properties was achieved in one electrical tree degradation experiment.

[0057] The sample preparation process is as follows: 1. Place the fiber in the designed fiber slot of the mold. The fiber should be longer than the length of the mold. After controlling the position, stick the outer ends of the fiber to the outside of the mold to fix the fiber position.

[0058] 2. Use sandpaper to polish a high-voltage needle electrode, and control the needle tip curvature diameter to 5±1μm. Place the polished needle electrode in an ethanol solution and ultrasonically clean it for 30 minutes. Place the cleaned high-voltage needle electrode in the designed mold needle electrode slot, and then seal the fiber slot and needle electrode slot with silicone rubber.

[0059] 3. Pour the prepared resin into the mold with fibers and electrodes, complete the resin curing according to the designed curing process, and prepare the electrical tree degradation test specimen.

[0060] Among them, the epoxy resin formula is: bisphenol A epoxy resin: methyl tetrahydrophthalic anhydride: 2-ethyl-4-methylimidazole = 100:85:0.5.

[0061] The curing process is as follows: ① Mix epoxy resin, methyltetrahydrophthalic anhydride and 2-ethyl-4-methylimidazole and heat at 60℃ for 30 minutes, stir evenly and then vacuum degas for 30 minutes. ② After pouring, keep the temperature at 80℃ for 30 minutes, 120℃ for 1 hour, and 140℃ for 1 hour.

[0062] 4. Use sandpaper to polish the bottom of the sample, control the needle-plate distance to 1±0.1mm, and ensure good contact between the sample and the ground electrode. Then paste a 100μm thick copper foil on the bottom of the sample, and the copper foil is connected to the ground electrode.

[0063] 5. Connect the high-voltage needle electrode and the ground electrode to the high-voltage power supply and the ground wire respectively, apply 16kV power frequency voltage, and pressurize until breakdown occurs. Use a microscope to observe the growth of electrical dendrites inside the electrode.

[0064] 6. Statistical data are collected on characteristic parameters such as the growth rate, morphology, and breakdown time of electrical dendrites, and the statistical data are analyzed to evaluate the fiber / resin matrix interface performance.

[0065] Table 1 is a statistical table of breakdown time of single fiber electrical tree samples.

[0066] It can be seen from Table 1 that after vacuum drying and dehumidification treatment, the breakdown time of the aramid fiber / epoxy resin sample is prolonged and the interface performance is improved.

[0067] Figure 6 and Figure 7 The following are schematic diagrams of the electrical tree morphology of group A and group B samples after breakdown. It can be seen that compared with the untreated samples, the aramid fiber / epoxy resin samples treated with vacuum drying and dehumidification present different electrical tree morphology: the electrical tree has more branches, darker color, and the thickness of the breakdown channel is more uniform. The difference in electrical tree morphology reflects the change in interface performance.

[0068] Figure 8 This is a schematic diagram of the electrical tree development process of the single fiber sample in group B.

[0069] Table 2 shows the shear strength of the interface between group B and group C fibers and epoxy resin.

[0070] It can be seen from Table 2 that the interface performance of group C fibers after plasma treatment is better.

[0071] Fig. 9The figure is a schematic diagram of the electrical tree morphology after the double-fiber sample is punctured. The fibers below the needle electrode are group B fibers, and the fibers above the needle electrode are group C fibers. It can be seen that in the same sample, the electrical tree tends to grow and puncture along the interface of group B fiber / resin with poor performance. The breakdown path of the electrical tree reflects the quality of the interface performance.

[0072] In summary, the above embodiments show that the degradation experimental method of an electrical tree specimen prepared by a fiber-reinforced resin disclosed in the embodiments of the present invention has the following advantages: by designing a curing mold and a sample preparation method, the experimental interference factors such as the needle electrode direction-fiber direction angle, the number of fibers and the needle-fiber straight-line distance are controlled, so that the interface performance is used as the only variable; a needle-plate electrode system with specific fiber, resin matrix type and fiber / resin matrix interface state is prepared, which can simulate the internal defects of fiber-reinforced resin materials under different interface composition structures and interface states, and provides a new method for observing the electrical tree degradation of fiber-reinforced epoxy composites affected by interface performance and studying the insulation failure mechanism of composite materials; by using fibers and matrices of different materials, fibers of different diameters, etc., the interface composition structure can be regulated; by prefabricating different interface defects, using different modification methods to pretreat the fibers, etc., the interface state can be regulated.

[0073] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0074] In addition, it should be noted that in the description of the present invention, 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 direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0075] 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 mold for preparing electrical tree specimens for resin degradation testing, characterized in that: The invention comprises a mould body, wherein the mould body is provided with a resin dipping tank and a fiber tank and a needle electrode tank which penetrate the mould body in the transverse direction and are connected with the resin dipping tank. The resin dipping tank separates the top surface of the mould body into a first side surface and a second side surface. The fiber tank is arranged to penetrate the first side surface and the second side surface. The needle electrode tank is arranged to penetrate the first side surface, and the width of the first side surface is greater than the width of the second side surface. The fiber tank is used to place the fiber. The needle electrode tank is used to place the high-voltage needle electrode. The side wall of the resin dipping tank facing the first longitudinal end of the mould body forms an obtuse angle with the bottom of the resin dipping tank, forming an inclined surface structure.

2. The mold for preparing electrical tree specimens for resin degradation test according to claim 1, characterized in that: The fiber slot and the needle electrode slot are combined into a first pair of slots extending through the first side surface and the second side surface, and the fiber and the high-voltage needle electrode are placed in the first pair of slots; preferably, the width of the first pair of slots matches the width of the high-voltage needle electrode.

3. The mold for preparing electrical tree specimens for resin degradation test according to claim 2, characterized in that: The first pair of notches includes two notches, one is arranged on the first side surface, and the other is arranged on the second side surface, the fiber is placed in the two notches, and the high-voltage needle electrode is placed in the notch on the first side surface; the two notches are equidistant from the side wall of the second longitudinal end of the mold body toward the dipping tank.

4. The mold for preparing electrical tree specimens for resin degradation test according to claim 1, characterized in that: The fiber groove is a second pair of grooves that pass through the first side surface and the second side surface, and the needle electrode groove is a third pair of grooves that pass through the first side surface, and the second pair of grooves and the third pair of grooves are arranged in parallel. When the fiber is placed in the second pair of grooves, it can pass through the first side surface and the second side surface. When the high-voltage needle electrode is placed in the third pair of grooves, it is placed at the position of the first side surface.

5. The mold for preparing electrical tree specimens for resin degradation test according to claim 4, characterized in that: The width of the second pair of notches matches the width of the high-voltage needle electrode.

6. An electrical tree specimen for resin degradation test, characterized in that: The method is prepared by using the mold described in any one of claims 1 to 5.

7. A method for testing degradation of electrical tree specimens, characterized in that: The electrical tree specimen according to claim 6 comprises: Prepare electrical tree specimens of different shapes, and use multiple molds to prepare multiple electrical tree specimens whose internal fibers and high-voltage needle electrode arrangements meet the experimental requirements; Observe the growth morphology of electrical dendrites, observe the development process of electrical dendrites with a microscope, and record the morphological graphs; Select node graphs for analysis, select multiple time node graphs for analysis, and select breakdown time graphs for analysis.

8. The electrical tree specimen degradation test method according to claim 7, characterized in that: The method for preparing the electrical tree specimen comprises: Place the fiber in the fiber slot, and after controlling the position, stick the outer ends of the fiber to the outside of the mold body to fix the fiber position; Place the high-voltage needle electrode, clean the pre-polished high-voltage needle electrode to remove impurities, place it in the needle electrode groove, and then seal the limit groove and the needle electrode groove; Prepare the sample, pour the prepared resin into the dipping tank with the fiber and the electrode, complete the resin curing according to the designed curing process, and prepare the sample for the electrical tree degradation experiment; Grind the sample, grind the bottom of the sample, control the needle-plate distance to meet the preset requirements, ensure good contact between the sample and the ground electrode, and stick copper foil on the bottom of the sample, which is connected to the ground electrode.

9. The electrical tree specimen degradation test method according to claim 8, characterized in that: The high-voltage needle electrode is polished to control the needle tip curvature diameter to be 5±1 μm, or to reach a preset diameter range.

10. The electrical tree specimen degradation test method according to claim 7, characterized in that: The prepared electrical trees include electrical trees with single fiber and single interface and electrical trees with double fibers and double interfaces.

Images