Anti-corona filling glue with low relative dielectric constant and preparation method

Abstract

The present invention belongs to the field of corona protection technology for electromechanical equipment, specifically relating to an anti-corona filler with a low relative dielectric constant and a preparation method. The present invention first provides an anti-corona filler, which is prepared by mixing an epoxy adhesive and a filler. The epoxy adhesive comprises a component A and a component B. The filler is nano-SiO2 powder, and the epoxy adhesive component A is a bisphenol A epoxy resin; the epoxy adhesive component B comprises a composite curing agent and a diluent. The anti-corona filler provided by the present invention has a low relative dielectric constant, which can reduce the electric field borne by air, making it less susceptible to breakdown, and thus suitable for use in high-altitude areas with low air density.

Description

[0001] Divisional application

[0002] This application is a divisional application based on the Chinese invention patent application with application number CN2024105249832, application date April 26, 2024, and invention name “Anti-corona glue and preparation method for high-altitude large hydropower equipment”. Technical Field

[0003] The invention belongs to the technical field of anti-corona of electromechanical equipment, and particularly relates to an anti-corona filling glue with a low relative dielectric constant and a preparation method thereof. Background Art

[0004] Corona discharge is a phenomenon in which the electric field strength near high-voltage electrical equipment or live conductors exceeds the breakdown voltage of air, causing localized air ionization and current discharge. Corona discharge can cause serious damage to equipment. Corona discharge in motors is primarily caused by uneven electric field distribution or excessive local field strength in certain areas of the winding insulation surface, leading to ionization of the surrounding air. This is a localized discharge, resulting in a glow discharge. Small gaps between insulating fixings (such as spacers and felt), between structural components and stator bars, and surface defects such as burrs accelerate the occurrence and development of corona discharge. Long-term corona discharge is one of the main causes of damage to the stator bar insulation layer, leading to eventual breakdown. This ultimately shortens the generator's service life and poses a serious threat to its safe operation. In recent years, with the continuous increase in the rated capacity and rated voltage of generator sets, the prevention and control of corona in the stator windings of air-cooled motors, especially hydro-turbine generators, has become a global technical challenge that urgently needs to be solved. The rapid construction and commissioning of hydropower generators in high-altitude, cold regions such as Tibet, Qinghai, and Xinjiang has led to higher requirements for insulation technology for these high-altitude units. This is because low air pressure and density at high altitudes can reduce the surface corona discharge voltage of the stator bars and windings of large-capacity hydropower generators (initiating corona discharge even before the normal operating voltage is reached). This makes the problem of corona prevention in large-capacity hydropower generator stator windings even more severe in these scenarios. Insulating equipment with an insulating layer is a key method for preventing corona discharge.

[0005] Patent publication number CN103160183A, entitled "Method for Preparing Nano-Corona Anti-Corona Paint," discloses a nano-corona anti-corona paint whose ingredients include epoxy resin, organic montmorillonite, toluene or xylene, and silicon carbide powder. The mass of silicon carbide powder added in this patent is 3-4 times that of the epoxy resin. The technical problem addressed by this patent is primarily to improve the mechanical and heat resistance of the anti-corona paint. The anti-corona paint disclosed in this patent achieves a heat resistance rating of F (155°C). However, this performance does not meet the requirements for use in extremely cold and damp weather conditions. Patent publication number CN108976991A, entitled "A High-Resistance Anti-Corona Paint for High-Voltage Motor Coils and Its Preparation Method," discloses a high-resistance anti-corona paint whose ingredients include epoxy resin, honeycomb silica nanotubes, polyamide resin, and toluene or xylene. The amount of honeycomb silica nanotubes added is less than 0.1%. The principle is that the hollow structure of the nanotubes has very good elasticity when slightly contracting and expanding, so it can significantly improve the high- and low-temperature impact resistance of the high-resistance anti-corona paint layer. However, this high-resistance anti-corona paint cannot solve the problem of corona discharge in the stator windings of large-capacity hydro-turbine generators caused by low air pressure and air density, which reduces the surface discharge voltage of the stator bars and stator windings. In addition, the air density at high altitudes is low, and the air is more easily broken down, that is, it is more prone to corona discharge.

[0006] In summary, it is necessary to develop anti-corona materials with low relative dielectric constants. Such materials can share part of the electric field borne by the air, making the air less likely to be broken down and thus less likely to cause corona discharge. Summary of the Invention

[0007] The object of the present invention is to provide an anti-corona filling glue with a low relative dielectric constant and a preparation method thereof, so as to partially solve or alleviate the above-mentioned deficiencies in the prior art. The present invention specifically adopts the following technical solutions.

[0008] On the one hand, the present invention provides a novel anti-corona filling adhesive.

[0009] The invention discloses an anti-corona filling adhesive with a low relative dielectric constant, wherein the anti-corona filling adhesive is prepared by mixing an epoxy adhesive and a filler, wherein the epoxy adhesive comprises an A component and a B component, wherein the filler is nano-SiO2 powder, and the nano-SiO2 powder is cross-linked with the epoxy adhesive A component, wherein the epoxy adhesive A component is a bisphenol A type epoxy resin; and the epoxy adhesive B component comprises a composite curing agent and a diluent, wherein the composite curing agent comprises polyamide, phenalkamine, 2,4,6-tris(diol)-1,2-diol, and 1,4-diol. The invention relates to a novel epoxy adhesive comprising a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin. The first epoxy resin comprises a first epoxy resin and a second epoxy resin.

[0010] As a preference, the composite curing agent consists of polyamide, phenalkamine and 2,4,6-tris(dimethylaminomethyl)phenol.

[0011] Furthermore, the chemical formulas of the components in the composite curing agent are as follows.

[0012] polyamide;

[0013] Phenalkamine (n=0,1,2…);

[0014] 2,4,6-Tris(dimethylaminomethyl)phenol.

[0015] Among them, polyamide and phenalkamine both contain primary amines, which react with epoxy groups to form amines (reaction 1); amines further react with epoxy groups to form tertiary amines (reaction 2); 2,4,6-tris(dimethylaminomethyl)phenol contains tertiary amines, which react with hydroxyl groups to form an etherification reaction, ultimately causing the epoxy system to form a three-dimensional network structure (reaction 3), as shown below.

[0016] .

[0017] As a preference, the weight percentage of the nano-SiO2 powder in the epoxy adhesive includes 1%, 1.5%, 2%, 2.5% or 3%.

[0018] It is understood that the ratio of the epoxy adhesive component A to the epoxy adhesive component B can be adjusted so that the viscosity of the colloid prepared by the epoxy adhesive component A and the epoxy adhesive component B is in the range of 180-380 mPa·s. Material ratios within this viscosity range and falling within the mass ratio of epoxy adhesive component A to epoxy adhesive component B of 10:3, 3:1.5, or 3:2 are all within the scope of protection of the present invention. Preferably, the mass ratio of the epoxy adhesive component A to the epoxy adhesive component B is 10:3.

[0019] As a preference, the mass ratio of the substances in component B of the epoxy adhesive is polyamide:phenalkamine:2,4,6-tris(dimethylaminomethyl)phenol:diluent is 35:9:4:12.

[0020] Furthermore, the particle size of the nano-SiO2 powder is in the range of 7-40 nm.

[0021] Furthermore, the specific surface area of ​​the nano-SiO2 powder is 120m 2 / g.

[0022] Another aspect of the present invention provides a method for preparing the novel anti-corona filling glue.

[0023] The method for preparing the anti-corona filling glue with low relative dielectric constant comprises the following steps:

[0024] S01: Mixing nano-SiO2 powder and epoxy adhesive component A and stirring evenly to obtain a first mixed solution;

[0025] S02: adding the epoxy adhesive component B to the first mixed solution and stirring evenly to obtain a second mixed solution, wherein the mass ratio of the epoxy adhesive component A to the epoxy adhesive component B is 10:3, 2:1 or 3:2; and the weight percentage of the nano-SiO2 powder in the epoxy adhesive is 1%-3%;

[0026] S03: placing the second mixed liquid in a vacuum drying environment, vacuuming to remove bubbles at room temperature, and then curing to obtain the anti-corona filling glue with a low relative dielectric constant.

[0027] Furthermore, in the S01, the nano-SiO2 powder and the epoxy adhesive component A are magnetically stirred at 60-80°C for 0.5-1h, and ultrasonically shaken to mix the components evenly.

[0028] Furthermore, in S02, the epoxy adhesive component B is added to the first mixed solution and magnetically stirred at room temperature for 10-15 minutes to obtain the second mixed solution.

[0029] Beneficial technical effects:

[0030] The present invention provides a low relative dielectric constant ( ε The anti-corona filling glue provided by the present invention has a minimum ε is 4.31, which can effectively share part of the electric field borne by the air (the ε 1), making it difficult for the air to be broken down, and thus difficult to initiate corona discharge. The anti-corona filling glue provided by the present invention was tested at altitudes of 2500m, 3000m, 3500m and 4000m. At 0°C and 30°C, its local discharge amount was less than that of the control group, and its corona inception voltage was higher than that of the control group, proving that it has a good anti-corona effect even in high-altitude areas with thin air. Furthermore, the electrical performance of the anti-corona filling glue was tested, proving that the anti-corona filling glue of the present invention has lower resistance and higher breakdown field strength than the control group.

[0031] The anti-corona filling adhesive provided by the present invention is primarily applied to the winding end binding structure of large hydropower units, filling and covering the air gaps and surface burrs at the binding sites. This improves the surface potential distribution of the windings, reduces the average and maximum field strength distribution of the stator bars and winding air gaps, and inhibits the generation and development of corona. In particular, it significantly reduces the electric field at the burr tips, effectively reducing the risk of discharge when burrs are present, thus achieving a corona-proof effect.

[0032] Finally, the preparation method provided by the present invention is simple and convenient, with controllable cost and good industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the embodiments or the description of the prior art. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the various elements or parts are not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without inventive work.

[0034] Figure 1 SEM images of anti-corona filling glue containing different weight percentages of nano-SiO2 powder (a is 0.5wt%, b is 1wt%, c is 1.5wt%, d is 2wt%, e is 2.5wt%, f is 3wt%, scale bar is 1μm);

[0035] Figure 2 The dielectric loss results of the anti-corona filling glue containing different amounts of nano-SiO2 powder are shown;

[0036] Figure 3 This is the electric field distribution diagram under the ideal binding state in the simulation test;

[0037] Figure 4 This is the electric field distribution diagram when bubbles exist in the simulation test;

[0038] Figure 5 This is the electric field distribution diagram when burrs exist in the simulation test;

[0039] Figure 6 This is a test chart of the physical and chemical properties of the anti-corona filling glue (A is the flow time and kinematic viscosity, B is the drying time, C is the pot life, and D is the overall shrinkage);

[0040] Figure 7 This is the electrical performance test diagram of the anti-corona filling glue;

[0041] Figure 8 Schematic diagram of the chemical reaction of the curing agent used in the present invention. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] As used herein, "and / or" includes any and all combinations of one or more of the associated listed items.

[0044] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0045] As used in this specification, the term "about" typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0046] In this specification, certain embodiments may be disclosed in a format that is within a range. It should be understood that this description of "within a range" is merely for convenience and brevity and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of a range should be considered to have specifically disclosed all possible subranges and individual numerical values ​​within this range. For example, the description of a range of 1-6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. Regardless of the breadth of the range, the above rules apply.

[0047] Example 1

[0048] This embodiment provides an example of a method for preparing a new type of anti-corona filling glue.

[0049] raw material:

[0050] Epoxy adhesive component A: bisphenol A epoxy resin.

[0051] Epoxy adhesive component B: composite curing agent: polyamide (PA), phenalkamine (PAA), 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30); diluent: resorcinol diglycidyl ether. The mass ratio of each substance is 35:9:4:12: polyamide:phenalkamine:2,4,6-tris(dimethylaminomethyl)phenol:resorcinol diglycidyl ether.

[0052] Filler: Nano-SiO 2， Specific surface area 120m 2 / g, particle size 7-40nm.

[0053] Preparation method of anti-corona filling glue (hereinafter referred to as anti-corona glue):

[0054] S01: After mixing nano-SiO2 powder and bisphenol A epoxy resin, magnetic stirring is carried out at 60°C for 1 hour to cross-link the nano-SiO2 and bisphenol A epoxy resin, and then ultrasonic vibration is carried out for 1 hour to mix them evenly (no bubbles in the mixed liquid) to obtain the first mixed liquid.

[0055] S02: Component B of the epoxy adhesive was added to the first mixed solution, and magnetic stirring was performed at room temperature for 10 minutes to obtain a second mixed solution, wherein component A was 3 kg and component B was 0.9 kg (mass ratio was 10:3).

[0056] S03: The second mixed liquid is placed in a vacuum drying oven, vacuumed at room temperature to remove bubbles, and then poured into a mold for curing. After curing at room temperature for 24 hours, the anti-corona filler adhesive sample for high-altitude large hydropower units is obtained. Depending on the weight percentage of nano-SiO2 powder in the epoxy adhesive, Sample 1 (0.5% wt), Sample 2 (1% wt), Sample 3 (1.5% wt), Sample 4 (2% wt), Sample 5 (2.5% wt), Sample 6 (3% wt), and a control sample (0% wt) are prepared, respectively. Samples 1 to 5 are collectively referred to as experimental samples.

[0057] It is understood that the specific proportions of the various substances added in the above preparation method are merely examples and not limitations.

[0058] How to use anti-corona filling glue:

[0059] The anti-corona filling glue prepared by the above method is applied to the winding end binding structure of a large hydropower unit.

[0060] Example 2

[0061] This example provides key performance verification of the anti-corona filling glue prepared in Example 1.

[0062] 2.1 Dispersion of nano-SiO2 powder in filler.

[0063] See Figure 1 . Figure 1 The scanning electron microscope (SEM) images of the anti-corona filling adhesive of samples 1-6 are shown in the figure. It can be seen that the dispersion of various added amounts of nano-SiO2 powder in the matrix epoxy adhesive (also called matrix adhesive) is relatively good, and no obvious agglomeration phenomenon is observed.

[0064] 2.2 Relative dielectric constant and dielectric loss test of anti-corona filling glue

[0065] Relative dielectric constant: It is the main parameter that reflects the dielectric properties or polarization properties of piezoelectric material dielectric under the action of electrostatic field, usually expressed as ε In the presence of AC voltage, the distribution of electric field strength in the medium is related to the medium ε Therefore, it is usually desirable for the insulation material coated on the motor to have a smaller ε , so the electric field strength shared by the insulating material will be relatively large. ε is 1, the electric field strength will be greater, and the air breakdown field strength itself is low, so when the insulating material ε The smaller it is, the more it can share part of the electric field borne by the air, making it less likely for the air to be broken down and thus less likely to cause corona discharge.

[0066] Dielectric loss: refers to the energy loss caused by the hysteresis effect of dielectric conductivity and dielectric polarization in the insulating material under the action of electric field, usually expressed as tan δ If the insulation material has significant loss, the electric field will cause the insulation material temperature to rise, causing it to age (become brittle, decompose, etc.). If the dielectric temperature continues to rise, it may even melt or burn the dielectric, causing it to lose its insulation capacity and ultimately lead to thermal breakdown.

[0067] Test method: According to GB / T 1409-2006 Recommended method for measuring the permittivity and dielectric loss factor of electrical insulating materials at power frequency, audio frequency and high frequency. The results are shown in Table 1 and Figure 2 .

[0068] Table 1 Dielectric loss results of anti-corona filling glue with different nano-SiO2 powders

[0069]

[0070] The calculation method of ε change rate: dielectric value of anti-corona glue with SiO2 powder added - dielectric value of anti-corona glue without SiO2 powder added / dielectric value of anti-corona glue without SiO2 powder added.

[0071] For example: Taking the case of adding 2.5wt% SiO2 powder as an example, the dielectric change rate = (4.31-4.76) / 4.76 = -9.45%.

[0072] Calculation method for tan δ change rate: Dielectric loss value of anti-corona glue with SiO2 powder added - Dielectric loss value of anti-corona glue without SiO2 powder added / Dielectric loss value of anti-corona glue without SiO2 powder added.

[0073] For example, taking the addition of 2.5wt% SiO2 powder as an example, the dielectric loss change rate = (0.00759-0.00654) / 0.00654 = 16.06%.

[0074] Conclusion: The anti-corona adhesive with the lowest relative dielectric constant is the preferred one. Therefore, the experimental sample (sample 5) with 2.5wt% nano-SiO2 powder added and the control sample (EP) without SiO2 powder added were selected for further testing.

[0075] 2.3 Simulation Test

[0076] The simulation test aims to detect the effect of anti-corona filling glue on the electric field at the binding structure of the hydropower unit winding end.

[0077] Simulation steps: (1) Build the model; (2) Set material properties; (3) Set boundary conditions; (4) Mesh generation; (5) Solve.

[0078] (1) Model construction: Use SOLIDWORK to construct a three-dimensional model of the stator winding; then import it into COMSOL software and select the "Current" interface under the "AC / DC" module in COMSOL; construct the air domain to obtain the stator winding simulation model.

[0079] (2) Setting material properties: Using COMSOL’s own material library and the results of material performance tests, assign corresponding material properties to each structure in the simulation model, such as setting the relative dielectric constant and conductivity of the material.

[0080] (3) Setting boundary conditions: The copper busbar conductor of the middle bar is set as the high-voltage end, and a voltage of 19.8 kV is applied; the copper busbar conductors of the upper and lower bars and the low-resistance anti-corona layer boundary of the three bars are set as the ground end, and a voltage of 0 V is applied.

[0081] (4) Mesh division: The copper busbar conductor and the main insulation layer adopt free tetrahedral mesh division, and the size is set to ultra-fine; the binding structure adopts a customized unit size, and the maximum unit size is 0.2 mm; the pad adopts a customized unit size, and the maximum unit size is 8 mm; the bubble and burr adopt a customized unit size, and the maximum unit size is 0.1 mm.

[0082] (5) Solution: Select the frequency domain solver as the solver, set the frequency study to 50 Hz, set the number of iterations to 1000, and the results of the COMSOL simulation developer should include potential, electric field, and loss, and the corresponding expressions are V, ec.normE, and ec.Qrh. The test results are shown in Table 2 and Figure 3-Figure 5 .

[0083] Table 2 Electric field results at the bubble and burr locations in the simulation test

[0084]

[0085] in conclusion: Figure 3 In the experiment, when the equipment end binding structure is in an ideal state, that is, assuming there are no defects such as bubbles and burrs, the anti-corona glue of the control sample group and the anti-corona glue of the experimental sample group have similar effects on the electric field distribution of the binding structure. The electric field distribution of the binding structure is relatively uniform, without obvious distortion areas. The maximum field strength is at the corner position of the wire rod and the pad. The electric field strength of the anti-corona glue of the control group and the anti-corona glue of the experimental group at this location is 1.24 kV / mm and 1.22 kV / mm, respectively. Figure 4 It shows that when bubbles exist, the electric field intensity at the bubbles is significantly higher than that at other parts, but the increase is not large. The maximum electric field intensity at the bubbles of the winding using the control sample is 1.68 kV / mm; the maximum electric field intensity at the bubbles of the winding using the experimental sample is 1.60 kV / mm, which is reduced by about 4.76%. Figure 5It can be seen that the presence of burrs poses a more serious threat to the winding. The maximum electric field strength at the burr tip in the control sample was 3.53 kV / mm, exceeding the normal breakdown field strength of air of 3 kV / mm, posing a risk of discharge. The maximum electric field strength at the burr tip in the experimental sample was 2.49 kV / mm, a reduction of approximately 29.37%. Clearly, anti-corona glue containing SiO2 powder effectively reduces the risk of discharge in the presence of burrs.

[0086] 2.4 Screening of ingredients for anti-corona fillers

[0087] Part 2.2 of this Example verified that the dielectric constant of the anti-corona adhesive containing 2.5 wt% nano-SiO2 was the lowest. The research and development team speculated that the dielectric constant of the anti-corona adhesive may be related to its viscosity, which is determined by the ratio of its components. Therefore, the team further screened and verified the ingredients of the anti-corona adhesive.

[0088] Table 3 Effect of adjustment of epoxy adhesive AB components on the performance of anti-corona adhesive

[0089]

[0090] Conclusion: Adjusting the A and B components of the epoxy adhesive results in changes in the matrix viscosity. This change in matrix viscosity further leads to differences in its interaction with and dispersion of nano-SiO2, thus affecting the relative dielectric constant of the resulting anti-corona adhesive. The results in Table 3 show that when the matrix viscosity is too high, the relative dielectric constant ε of the resulting anti-corona adhesive is higher. However, when the matrix viscosity ranges from approximately 180 to 380 mPa·s, the relative dielectric constant ε of the anti-corona adhesive is lower. The optimal mass ratio of the A:B components of the epoxy adhesive is 10:3.

[0091] Example 3

[0092] This example provides other performance verifications of the anti-corona filling glue prepared in Example 1.

[0093] 3.1 Physical and chemical properties testing of anti-corona filling glue

[0094] Test method: The filling glue of sample 5 and control sample was applied to the binding structure of the winding end of the large hydropower unit to fill and cover the air gap and surface burrs at the binding. The physical and chemical properties of the two samples were tested. Figure 6 .

[0095] in conclusion: Figure 6 A shows that at the same test distance, the control sample (EP) has a lower kinematic viscosity and therefore a shorter flow time; while the experimental sample has a higher viscosity and better retention. Figure 6Figure B shows that the control sample (EP) has a longer drying time, while the experimental samples have a shorter drying time, which matches the viscosity results. Figure 6 C shows that the shelf life of the experimental samples is shorter. Figure 6 D shows that the experimental samples have a lower total volume shrinkage. The control sample (EP) has a total volume shrinkage of 4.39%, while Sample 5 has a total volume shrinkage of 2.75%. The lower total volume shrinkage of Sample 5 indicates that the filler can better cover the air gaps and surface burrs at the binding after drying.

[0096] It should be understood that the "pot life" referred to in this invention refers to the period from the time a two-component epoxy adhesive is mixed until it gels and becomes unusable. Gelation refers to the process by which the adhesive changes from a liquid to an unusable solid or semi-solid state. The pot life testing method used in this invention involves preparing the epoxy adhesive and placing it in a container. A stirring rod is then placed vertically in the container and slowly and evenly pulled upward. The pot life is determined when the adhesive and container are lifted more than 10 cm off the table.

[0097] 3.2 Electrical performance test of anti-corona filling compound

[0098] Test method: The breakdown field strength is tested in accordance with GB / T 1408.1-2006 Test methods for electric strength of insulating materials Part 1: Tests at power frequency; the comparative tracking index is tested in accordance with GB / T 4207-2022 Test method for tracking resistance index and comparative tracking index of solid insulating materials; the resistivity is tested in accordance with GB / T 1410-2006 Test method for volume resistivity and surface resistivity of solid insulating materials, see Figure 7 .

[0099] Conclusion: Overall, the experimental samples performed similarly to the control samples in terms of electrochemical index and resistivity, but the experimental samples had lower resistance and higher breakdown field strength, reaching 65.37 kV / mm, while the control sample had a breakdown field strength of 59.04 kV / mm. This indicates that the anti-corona filler with the addition of nano-SiO2 is less susceptible to breakdown.

[0100] 3.3 Insulation resistance test of anti-corona filling compound

[0101] Test method: The test was conducted in accordance with GB / T 20833.4-2021, Rotating Electrical Machine Winding Insulation — Part 4: Measurement of Insulation Resistance and Polarization Index, at an altitude of 2000m and room temperature. The results are shown in Table 4.

[0102] Table 4 Insulation resistance of anti-corona filling compound

[0103]

[0104] Conclusion: The anti-corona glue with the addition of nano-SiO2 improves the insulation performance of the binding structure at the winding end of the hydropower unit.

[0105] 3.4 Partial discharge detection

[0106] Testing methods: Tests were conducted in accordance with IEC-270 at altitudes of 2500m, 3000m, 3500m, and 4000m, and at temperatures of 0°C and 30°C. At high altitudes, the air density is lower, making it more susceptible to breakdown and causing corona discharge. In this experiment, a partial discharge exceeding 10,000 pF was considered the start of discharge. Results are shown in Tables 5 and 6.

[0107] Table 5 Partial discharge at 0℃

[0108]

[0109] Table 6 Partial discharge at 30℃

[0110]

[0111] Conclusion: The results show that Sample 5's anti-corona glue significantly reduces partial discharge compared to the control sample's anti-corona glue at both 0°C and 30°C. In particular, at a test voltage of 1Un, the control sample reached nearly 10,000pF at just 2,500m, indicating imminent discharge. Sample 5, however, maintained no discharge at an altitude of 3,500m at 0°C and at an altitude of 4,000m at 30°C.

[0112] 3.5 Corona onset voltage detection

[0113] Testing method: The test was conducted in accordance with "DL / T 298-2011 Guidelines for Corona Detection and Assessment of Generator Stator Winding Ends." Testing was performed using an ultraviolet imager, with the voltage at which the photon count exceeded 1500 being considered the corona onset voltage. Testing conditions were at altitudes of 2500m, 3000m, 3500m, and 4000m, and at temperatures of 0°C and 30°C. The results are shown in Tables 7 and 8.

[0114] Table 7 Corona onset voltage at 0℃

[0115]

[0116] Table 8 Corona onset voltage at 30℃

[0117]

[0118] Conclusion: Compared with the anti-corona glue of the control sample, the anti-corona glue of sample 5 increases the corona inception voltage at the binding structure of the hydropower unit winding end, and improves its anti-corona performance under high altitude conditions.

[0119] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. An anti-corona filling glue with low relative dielectric constant, characterized in that: The anti-corona filling glue is prepared by mixing an epoxy adhesive and a filler. The epoxy adhesive includes a component A and a component B. The filler is nano-SiO2 powder. The nano-SiO2 powder is cross-linked with the epoxy adhesive component A. The epoxy adhesive component A is a bisphenol A epoxy resin. The epoxy adhesive component B includes a composite curing agent and a diluent. The composite curing agent includes polyamide, phenolic amine, 2,4,6-tris (dimethylaminomethyl) phenol. The diluent is resorcinol diglycidyl ether; the mass ratio of the substances in the epoxy adhesive component B is 35-40:9-14:4-9:12-17 of polyamide:phenalkamine:2,4,6-tris(dimethylaminomethyl)phenol:diluent; the mass ratio of the epoxy adhesive component A to the epoxy adhesive component B includes 10:3, 3:1.5 or 3:2; the viscosity of the colloid prepared by the epoxy adhesive components A and B is in the range of 180-380 mPa·s; and the weight percentage of the nano-SiO2 powder in the epoxy adhesive is 1%-3%.

2. The anti-corona filling adhesive with low relative dielectric constant according to claim 1, characterized in that: The weight percentage of the nano-SiO2 powder in the epoxy adhesive includes 1%, 1.5%, 2%, 2.5% or 3%.

3. The anti-corona filling adhesive with low relative dielectric constant according to claim 1, characterized in that: The mass ratio of the epoxy adhesive component A to the epoxy adhesive component B is 10:

3.

4. The anti-corona filling adhesive with low relative dielectric constant according to claim 1, characterized in that: The mass ratio of the substances in the epoxy adhesive component B is 35:9:4:12:polyamide:phenalkamine:2,4,6-tris(dimethylaminomethyl)phenol:diluent.

5. The anti-corona filling adhesive with low relative dielectric constant according to claim 1, characterized in that: The particle size of the nano-SiO2 powder is in the range of 7-40 nm.

6. The anti-corona filling adhesive with low relative dielectric constant according to claim 1, characterized in that: The specific surface area of ​​the nano-SiO2 powder is 120m 2 / g.

7. The method for preparing the anti-corona filling adhesive with low relative dielectric constant according to any one of claims 1 to 6, characterized in that: The following steps are involved: S01: Mixing nano-SiO2 powder and epoxy adhesive component A and stirring evenly to obtain a first mixed solution; S02: adding the epoxy adhesive component B to the first mixed solution and stirring evenly to obtain a second mixed solution, wherein the mass ratio of the epoxy adhesive component A to the epoxy adhesive component B is 10:3, 2:1 or 3:2; and the weight percentage of the nano-SiO2 powder in the epoxy adhesive is 1%-3%; S03: placing the second mixed liquid in a vacuum drying environment, vacuuming to remove bubbles at room temperature, and then curing to obtain the anti-corona filling glue with a low relative dielectric constant.

8. The preparation method according to claim 7, wherein In the S01, the nano-SiO2 powder and the epoxy adhesive component A are magnetically stirred at 60-80°C for 0.5-1h, and ultrasonically shaken to mix the components evenly.

9. The preparation method according to claim 7, wherein In S02, the epoxy adhesive component B is added to the first mixed solution and magnetically stirred at room temperature for 10-15 minutes to obtain the second mixed solution.

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