Binary hydrocarbon insulating liquids, methods of making and use in oil-immersed transformers

Abstract

The application discloses a binary hydrocarbon insulating liquid, a preparation method and application in oil-immersed transformers, and belongs to the technical field of liquid insulating dielectric. The binary hydrocarbon insulating liquid is composed of the following components in percentage by volume: short-chain low-branched alkane: 10%-30%; the rest is long-chain multi-branched alkane, and the total is 100%; in the short-chain low-branched alkane, the number of carbon atoms in the first main chain is 15-20, the number of the first branch is 1-2, the first branch is methyl and / or ethyl, and the first branch is distributed at the end of the first main chain; in the long-chain multi-branched alkane, the number of carbon atoms in the second main chain is 21-28, the number of the second branch is 2-6, and the second branch is methyl and / or ethyl. The binary hydrocarbon insulating liquid has excellent lightning impulse insulation performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid insulation dielectric, more particularly to a binary hydrocarbon insulation liquid, a preparation method and application in oil-immersed transformers. BACKGROUND

[0002] With the rapid development of ultra-high voltage power grid construction and the continuous improvement of power equipment capacity, oil-immersed power transformers are facing more stringent lightning impulse insulation performance requirements. Lightning impulse insulation performance is a key indicator for measuring the insulation characteristics of insulation liquid under transient high voltage impulse, and is directly related to the safe operation of power equipment under extreme weather conditions such as lightning.

[0003] Although traditional mineral insulation oil has relatively good lightning impulse breakdown voltage, it has poor environmental performance, low biodegradation rate, and long-term pollution to the environment after leakage, which cannot meet the requirements of green power development. In addition, the thermal stability of mineral oil is poor, which can easily age during long-term operation, resulting in gradual degradation of lightning impulse insulation performance.

[0004] In recent years, in order to solve the environmental problem of mineral oil, natural esters and synthetic esters and other bio-based insulation oils have become a research hotspot. However, ester-based insulation oil has a fatal technical defect: the lightning impulse breakdown voltage is significantly lower than that of mineral oil, about 40% to 60% of that of mineral oil. This performance shortcoming seriously restricts the application of ester-based insulation oil in ultra-high voltage and large-capacity power equipment, and becomes a key technical bottleneck hindering its promotion. SUMMARY

[0005] To solve the above problems, the present application provides a binary hydrocarbon insulation liquid, a preparation method and application in oil-immersed transformers. The binary hydrocarbon insulation liquid has excellent lightning impulse insulation performance, and also has obvious advantages in environmental performance, while meeting the requirements of current insulation oil related standards, and has good application prospects in high voltage grade and large-capacity power equipment.

[0006] The first object of the present application is to provide a binary hydrocarbon insulation liquid, which is composed of the following components by volume percentage:

[0007] Short-chain low-branched alkane: 10% to 30%; the rest is long-chain multi-branched alkane, totaling 100%.

[0008] In the short-chain low-branched alkane, the number of first main chain carbon atoms is 15 to 20, the number of first branch chains is 1 to 2, the first branch chains are methyl and / or ethyl, and the first branch chains are distributed at the end of the first main chain.

[0009] In the long-chain multi-branched alkane, the number of second main chain carbon atoms is 21 to 28, the number of second branch chains is 2 to 6, and the second branch chains are methyl and / or ethyl.

[0010] The volume resistivity of the short-chain low-branched alkane is 1.3*10 12 Ω·m, and the lightning impulse breakdown voltage is 177.29 kV / mm. With the increase of the number of first main chain carbon atoms in the short-chain low-branched alkane, the lightning impulse insulation performance slightly decreases, but the thermal stability and flash point significantly increase. When the first branch is only a methyl group, the intermolecular distance is moderate, the lightning impulse insulation performance is excellent, and the biodegradability is good. When the first branch is only an ethyl group, the steric hindrance effect is enhanced, the lightning impulse insulation performance is further improved, but the biodegradability slightly decreases. When the first branch is a methyl group and an ethyl group, the performance indicators tend to be balanced.

[0011] In the long-chain multi-branched alkane, the second branch is arranged at a position at least one carbon atom away from the end of the second main chain. In the long-chain multi-branched alkane, the second branch is irregularly distributed, and the volume resistivity is 1.7*10 12 Ω·m, and the lightning impulse breakdown voltage is 162.89 kV / mm. With the increase of the number of second main chain carbon atoms in the long-chain multi-branched alkane, the molecular viscosity gradually increases, the thermal stability is improved, but the impulse insulation performance and biodegradability gradually decrease. When the second branch is only a methyl group, a moderate steric protection structure is formed, the thermal stability is good, and the biodegradability remains at a high level. When the second branch is only an ethyl group, the steric hindrance effect is significant, the thermal stability is further improved, but the biodegradability decreases. When the second branch is a methyl group and an ethyl group, the comprehensive performance is more stable.

[0012] The present application realizes a unique synergistic effect mechanism at the molecular level by controlling the specific ratio of short-chain low-branched alkane and long-chain multi-branched alkane, and fundamentally solves the technical bottleneck of lightning impulse insulation performance of existing insulating liquids. The core of the compounding strategy of the present application is to use the high impulse insulation strength of the short-chain molecule as the performance basis, balance and optimize other key performance indicators by introducing an appropriate amount of long-chain multi-branched alkane, realize the molecular design concept of optimizing the inferior by the superior and synergistic effect, so that the lightning impulse breakdown voltage of the binary hydrocarbon insulating liquid obtained finally is significantly better than that of the long-chain multi-branched alkane alone, and the thermal stability, viscosity control and biodegradability are obviously better than those of the short-chain molecule alone.

[0013] Compared with the prior art, the core innovation of the application is the molecular design concept based on the lightning impulse insulation mechanism and the biodegradation mechanism. The alkane molecules selected by the application have a straight chain structure. Compared with the naphthenes and aromatic hydrocarbons commonly found in mineral oil, the straight chain alkane molecular structure is simple, the molecular chain is flexible, and the straight chain alkane is more easily recognized and degraded by a microbial enzyme system. Therefore, the molecular design based on the straight chain structure makes the application have more excellent biodegradation performance than traditional mineral oil, and the biodegradation rate is 72.9% to 78.7%, which is much higher than 30% of the mineral oil. The environmental pollution risk can be significantly reduced, and the higher requirements of green power equipment on environmental protection performance are met.

[0014] The application realizes the balance of environmental protection performance, high lightning impulse insulation performance and high volume resistivity by controlling the specific proportion of two types of alkanes with different chain lengths and branching degrees, which is not realized in the existing mineral oil, ester oil and their mixtures. The application directly faces the application requirements of ultra-high voltage and large-capacity power equipment, and the performance parameters are better than those of the existing mineral oil and ester insulation oil. The application has high biodegradability, and environmental protection and safety are considered. The binary hydrocarbon insulation liquid with high insulation resistance and strong impulse insulation characteristics is better than the traditional mineral oil, the existing ester insulation oil and the mixed insulation oil in terms of lightning impulse voltage resistance, significantly improves the insulation safety and operation reliability of the power equipment, and other performances meet the requirements of the existing insulation oil related standards. The binary hydrocarbon insulation liquid can replace the existing mineral insulation oil for high voltage grade and large-capacity power equipment such as transformers, and has good industrial feasibility and application prospect.

[0015] In a preferred embodiment of the application, the short-chain low-branching alkane is 20% to 30%, and the rest is long-chain multi-branching alkane, and the total is 100%.

[0016] In a preferred embodiment of the application, in the short-chain low-branching alkane, the number of first main chain carbon atoms is 18, and the number of first branch chains is 1.

[0017] In a preferred embodiment of the application, in the long-chain multi-branching alkane, the number of second main chain carbon atoms is 23, and the number of second branch chains is 3.

[0018] In a preferred embodiment of the application, the structure of the short-chain low-branching alkane is as follows:

[0019] .

[0020] In a preferred embodiment of the application, the structure of the long-chain multi-branching alkane is as follows:

[0021] .

[0022] The second object of the present application is to provide a preparation method of the binary hydrocarbon insulating liquid, comprising the following steps:

[0023] After the short-chain low-branched alkane and the long-chain multi-branched alkane are uniformly mixed, the binary hydrocarbon insulating liquid is obtained by filtering and drying.

[0024] The third object of the present application is to provide the application of the binary hydrocarbon insulating liquid in oil-immersed transformers. The performance parameters of the binary hydrocarbon insulating liquid in the present application meet the requirements of IEC60296, and the binary hydrocarbon insulating liquid can be used in environmentally friendly oil-immersed high-voltage transformers.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] The present application provides a binary hydrocarbon insulating liquid, comprising the following components: short-chain low-branched alkane: 10vol.%-30vol.%; long-chain multi-branched alkane: 70vol.%-90vol.%. The present application realizes the balance of environmental performance, high lightning impulse insulation performance and high volume resistivity by controlling the specific ratio of two types of hydrocarbon liquids with different chain lengths and branching degrees. The short-chain low-branched alkane molecules have small molecular volume and weak intermolecular forces, and can quickly rearrange under the action of a strong electric field in lightning impulse, providing a fast dissipation channel for electric charges. The low viscosity characteristics promote ion migration and prevent the accumulation of electric charges in local areas. The long-chain multi-branched alkane molecules form a three-dimensional shielding structure, effectively dispersing and homogenizing the electric field distribution and avoiding local electric field concentration. At the same time, the three-dimensional molecular network constructed by the multi-branched alkane provides a stable insulating matrix, significantly enhancing the overall dielectric strength. When the short-chain component is controlled within the key ratio range of 10vol.%-30vol.%, the excellent lightning impulse insulation performance of the short-chain molecules can be fully utilized, and better thermal stability, viscosity characteristics and environmental performance can be obtained on the basis of maintaining high impulse insulation strength through the dilution and modification of the long-chain multi-branched alkane.

[0027] Traditional ester insulating oil contains polar C=O groups. Under a strong electric field, the lone pair electrons of the oxygen atom migrate to the carbon atom, forming a transient dipole, increasing the risk of charge accumulation and local electric field distortion, and resulting in a significant decrease in breakdown voltage. Although mineral oil is a non-polar molecule, it lacks a synergistic design at the molecular level and cannot achieve the best match between charge transmission and structural stability by relying on a single chain length of saturated alkane. Moreover, the naphthenic and aromatic hydrocarbon structures of mineral oil result in poor biodegradability.

[0028] The non-polar straight-chain alkane molecules of the present application completely eliminate the negative effects of polar groups, and through the double-chain length gradient design and branched chain structure optimization, the methyl / ethyl branched chain is distributed at the end of the main chain, and the number of branched chains is controlled to be 1-2, which fully plays the dual advantages of high ionization energy and high impulse insulation of short-chain low-branched alkane molecules. Accurate control of the ratio is crucial: when the short-chain low-branched alkane is less than 10 vol.%, its excellent impulse insulation performance cannot be fully played, and the overall performance is mainly limited by the lower impulse insulation performance of the long-chain multi-branched alkane; when the short-chain low-branched alkane is more than 30 vol.%, although the impulse insulation performance is further improved, it will cause problems such as too low viscosity and flash point drop, affecting the comprehensive performance of actual application. Therefore, the volume percentage of short-chain low-branched alkane in the ratio range of 10%-30% realizes the best balance point of high impulse insulation performance and comprehensive application performance, and the present application provides a new scientific guidance for the molecular design of high-performance insulating liquid through the synergistic insulation theory of short-chain leading and long-chain auxiliary. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0030] For extra-high voltage and large-capacity power equipment, when using insulating oil, the key technical problems to be considered include: the contradiction between lightning impulse insulation performance and environmental degradation performance, traditional mineral oil has good impulse insulation performance, but the biodegradation rate is very low, about <30%, while bio-based ester oil has high degradation rate but the lightning impulse breakdown voltage is significantly lower; the balance problem of electrical performance and flow heat dissipation performance, high molecular weight components can provide good insulation strength but will cause too high viscosity to affect heat dissipation, while low molecular weight components have good flowability but may have the safety hazard of low flash point; the coordination problem of long-term running stability and initial high performance, the insulating liquid needs to maintain excellent initial electrical performance while ensuring long-term thermal stability and anti-aging performance.

[0031] In addition, among the insulating oils disclosed in the prior art, patent CN101198682B proposes an oil formulation for electrical insulation containing a base oil component and additives, the base oil being a paraffin base oil, but does not specify the ratio of short chain / long chain and the design of molecular branching structure, and patent CN101198682B improves the oxidation stability and low temperature performance by adding antioxidants and other additives, without emphasizing the lightning impulse insulation performance. Patent CN119317689A proposes a hydrocarbon component, mainly for fuel, and the performance optimization focuses on viscosity, cloud point, density, etc., without emphasizing the lightning impulse insulation performance. The above patents do not consider the lightning impulse insulation performance, so the insulating oils designed in the prior art do not meet the application requirements of ultra-high voltage and large capacity power equipment.

[0032] The current technical gap is particularly reflected in the lack of systematic study of the influence of molecular chain length, branching degree and branching position on the impulse insulation performance of insulating oil. The length of the chain, the degree of branching and the branching position of the molecular structure are directly related to the ionization, electron affinity and excitation processes of the insulating oil, which in turn affect its impulse insulation performance. In addition, the synergistic effect between different components of the same kind, i.e. the proportion of physical mixing, also has an important influence on its performance, but has not been fully studied and applied.

[0033] Based on the above technical challenges, the present application selects a method of complexing double-chain-length straight-chain alkanes, and designs the polarity in the following aspects:

[0034] 1. Chain length selection principle, short-chain low-branching alkanes are selected as C 15 ~ C 28 Because this chain length range can provide sufficient thermal stability and appropriate flash point to meet the safe operation requirements of power equipment, and its large molecular volume is conducive to the formation of a stable insulating matrix, although the impulse insulation performance is relatively poor when used alone, it can effectively balance other key performance indicators in a complex system.

[0035] 2. Branching degree design principle, short-chain low-branching alkanes adopt low branching degree to appropriately reduce the symmetry of the molecules on the basis of maintaining high ionization energy, avoiding the crystallization tendency caused by excessive regular arrangement of the molecules, and the light branching helps to improve the low temperature flowability; long-chain multi-branching alkanes adopt multi-branching design mainly to destroy the linear structure of the molecules, prevent strong entanglement and aggregation between long-chain multi-branching alkanes, and ensure uniform dispersion in the complex system, and the multi-branching structure is conducive to increasing the number of attack sites of biodegradation enzymes.

[0036] 3. The key considerations for the selection of branched groups and positions include: the selection of methyl and / or ethyl as branched groups because these two alkyl groups have moderate steric hindrance effects, methyl has small volume and small steric hindrance, mainly plays the role of destroying the symmetry of the molecule and providing moderate steric protection, ethyl has slightly larger volume and can more effectively prevent intermolecular π-π stacking and van der Waals interaction, and if a combination of methyl and ethyl is used, the intermolecular distance and interaction strength can be precisely regulated.

[0037] The first branched position selection of the short-chain low-branched alkane at the end of the main chain rather than in the middle is based on the consideration of the electron transport mechanism. The end branched chain does not interfere with the conjugated electron transport path of the main chain, maintaining the electrical continuity of the molecule, while the middle branched chain causes interruption and scattering of electron transport, reducing the dielectric properties of the molecule. In addition, the end branched chain can also provide effective steric protection to prevent oxidation and polymerization of the end group of the molecule. This carefully designed molecular structure enables the short-chain molecule to provide excellent impact insulation performance while maintaining good chemical stability, and the long-chain multi-branched alkane ensures thermal stability and environmental degradation, and forms good compatibility with the short-chain molecule, ultimately achieving a multiple optimization balance of electrical performance, thermal stability, environmental performance and application suitability.

[0038] The short-chain low-branched alkane and the long-chain multi-branched alkane used in the embodiments of the present application are purchased from Shanghai Dow Chemical Co., Ltd. In Embodiments 1-3, the model of the short-chain low-branched alkane is 2835H, and the model of the long-chain multi-branched alkane is ICCSYN3. In Embodiment 4, the model of the short-chain low-branched alkane is 2018H, and in Embodiment 5, the model of the long-chain multi-branched alkane is ICCSYN4.

[0039] Embodiment 1

[0040] The present embodiment proposes a binary hydrocarbon insulating liquid with high insulation resistance and strong impact insulation characteristics, which is composed of the following components by volume percentage:

[0041] Short-chain low-branched alkane: 30%; long-chain multi-branched alkane: 70%.

[0042] The molecular formula of the short-chain low-branched alkane is C 19 H 40 .

[0043] The structural formula is as follows:

[0044] .

[0045] The molecular formula of the long-chain multi-branched alkane is C 25 H 52 .

[0046] The structural formula is as follows:

[0047] .

[0048] The short-chain low-branched alkane and the long-chain multi-branched alkane are mixed in the above proportions, and then filtered and dried to obtain a binary hydrocarbon insulating liquid. The purpose of filtering and drying is to remove moisture, acidic substances, and impurity particles, and the moisture content is reduced to below 20 ppm.

[0049] Example 2

[0050] This example proposes a binary hydrocarbon insulating liquid with high insulation resistance and strong impulse insulation characteristics, which is composed of the following components in volume percentage:

[0051] Short-chain low-branched alkane: 20%; long-chain multi-branched alkane: 80%.

[0052] The molecular formula of the short-chain low-branched alkane is C 19 H 40 .

[0053] The structural formula is as follows:

[0054] .

[0055] The molecular formula of the long-chain multi-branched alkane is C 25 H 52 .

[0056] The structural formula is as follows:

[0057] .

[0058] The short-chain low-branched alkane and the long-chain multi-branched alkane are mixed in the above proportions, and then filtered and dried to obtain a binary hydrocarbon insulating liquid. The purpose of filtering and drying is to remove moisture, acidic substances, and impurity particles, and the moisture content is reduced to below 20 ppm.

[0059] Example 3

[0060] This example proposes a binary hydrocarbon insulating liquid with high insulation resistance and strong impulse insulation characteristics, which is composed of the following components in volume percentage:

[0061] Short-chain low-branched alkane: 10%; long-chain multi-branched alkane: 90%.

[0062] The molecular formula of the short-chain low-branched alkane is C 19 H 40 .

[0063] The structural formula is as follows:

[0064] .

[0065] The molecular formula of the long-chain multi-branched alkane is C 25H 52 .

[0066] The structural formula is as follows:

[0067] .

[0068] After mixing the short-chain low-branched alkane and the long-chain multi-branched alkane in the above proportions, filter and dry to obtain the binary hydrocarbon insulating liquid. The purpose of filtering and drying is to remove moisture, acidic substances, and impurity particles, and the moisture can be reduced to below 20 ppm.

[0069] Example 4

[0070] This example proposes a binary hydrocarbon insulating liquid with high insulation resistance and strong impulse insulation characteristics, which is composed of the following components in volume percentage:

[0071] Short-chain low-branched alkane: 10%; long-chain multi-branched alkane: 90%.

[0072] The molecular formula of the short-chain low-branched alkane is C 17 H 36 .

[0073] The structural formula is as follows:

[0074] .

[0075] The molecular formula of the long-chain multi-branched alkane is C 25 H 52 .

[0076] The structural formula is as follows:

[0077] .

[0078] After mixing the short-chain low-branched alkane and the long-chain multi-branched alkane in the above proportions, filter and dry to obtain the binary hydrocarbon insulating liquid. The purpose of filtering and drying is to remove moisture, acidic substances, and impurity particles, and the moisture can be reduced to below 20 ppm.

[0079] Example 5

[0080] This example proposes a binary hydrocarbon insulating liquid with high insulation resistance and strong impulse insulation characteristics, which is composed of the following components in volume percentage:

[0081] Short-chain low-branched alkane: 10%; long-chain multi-branched alkane: 90%.

[0082] The molecular formula of the short-chain low-branched alkane is C 19 H 40 .

[0083] The structural formula is as follows:

[0084] .

[0085] The long-chain, highly branched alkane has a molecular formula of C 28 H 58 .

[0086] The structure is as follows:

[0087] .

[0088] The short-chain, lowly branched alkane and the long-chain, highly branched alkane are mixed in the above proportions and filtered and dried to obtain a binary hydrocarbon insulating liquid. The purpose of filtering and drying is to remove moisture, acidic substances, and impurity particles, and the moisture can be reduced to below 20 ppm.

[0089] Comparative Example 1

[0090] The present comparative example proposes a binary hydrocarbon insulating liquid composed of the following components in volume percentage:

[0091] Short-chain, lowly branched alkane: 40%; long-chain, highly branched alkane: 60%.

[0092] The short-chain, lowly branched alkane has a molecular formula of C 19 H 40 .

[0093] The structure is as follows:

[0094] .

[0095] The long-chain, highly branched alkane has a molecular formula of C 25 H 52 .

[0096] The structure is as follows:

[0097] .

[0098] The short-chain, lowly branched alkane and the long-chain, highly branched alkane are mixed in the above proportions and filtered and dried to obtain a binary hydrocarbon insulating liquid. The purpose of filtering and drying is to remove moisture, acidic substances, and impurity particles, and the moisture can be reduced to below 20 ppm.

[0099] Comparative Example 2

[0100] The present comparative example proposes a binary hydrocarbon insulating liquid composed of the following components in volume percentage:

[0101] Short-chain, lowly branched alkane: 80%; long-chain, highly branched alkane: 20%.

[0102] The short-chain, lowly branched alkane has a molecular formula of C 19 H 40 .

[0103] The structural formula is as follows:

[0104] .

[0105] The long-chain multi-branched alkane has a molecular formula of C 25 H 52 .

[0106] The structural formula is as follows:

[0107] .

[0108] After the short-chain low-branched alkane and the long-chain multi-branched alkane are mixed in the above proportions, the binary hydrocarbon insulating liquid is obtained after filtration and drying. The purpose of filtration and drying is to remove moisture, acidic substances, and impurity particles, and the moisture can be reduced to below 20 ppm.

[0109] Comparative Example 3

[0110] The present comparative example proposes a binary hydrocarbon insulating liquid composed of the following components in volume percentage:

[0111] Short-chain low-branched alkane: 90%; long-chain multi-branched alkane: 10%.

[0112] The short-chain low-branched alkane has a molecular formula of C 19 H 40 .

[0113] The structural formula is as follows:

[0114] .

[0115] The long-chain multi-branched alkane has a molecular formula of C 25 H 52 .

[0116] The structural formula is as follows:

[0117] .

[0118] After the short-chain low-branched alkane and the long-chain multi-branched alkane are mixed in the above proportions, the binary hydrocarbon insulating liquid is obtained after filtration and drying. The purpose of filtration and drying is to remove moisture, acidic substances, and impurity particles, and the moisture can be reduced to below 20 ppm.

[0119] The binary hydrocarbon insulating liquid prepared in the above-mentioned examples 1-3 with high insulation resistance and strong impulse insulation characteristics was tested for key performance such as acid value, dielectric loss, flash point, volume resistivity and lightning impulse breakdown voltage, and compared with traditional mineral insulating oil, single short-chain low-branched alkane, single long-chain multi-branched alkane and comparative examples 1-3, and the results are shown in Tables 1 and 2. It should be noted that the single short-chain low-branched alkane, the single long-chain multi-branched alkane and the structural formula of example 1 are the same.

[0120] Table 1 Key performance parameters of binary hydrocarbon insulating liquid prepared in different examples

[0121]

[0122] Table 2 Key performance parameters of different control groups

[0123]

[0124] Table 3 Key performance parameters of binary hydrocarbon insulating liquid prepared in different comparative examples

[0125]

[0126] As can be seen from Tables 1-2, the volume resistivity and lightning impulse voltage of the binary hydrocarbon insulating liquid of examples 1, 2 and 3 are better than mineral oil, and other performance parameters meet the relevant standards of GB2536-2011, indicating that the binary hydrocarbon insulating liquid of the present application has high insulation resistance and strong impulse insulation characteristics, and the technical advantage is obvious. The performance indicators of the binary hydrocarbon insulating liquid of examples 1 and 2 are better than those of the traditional mineral insulating oil. Specifically, compared with 25# naphthenic mineral oil, the binary hydrocarbon insulating liquid of examples 1 and 2 has lower viscosity, and the pour point of the bio-based environmentally friendly insulating oil of examples 1 and 2 is 19℃ and 17℃ lower than that of 25# naphthenic mineral oil respectively, which has the ability to run more safely in cold regions. At the same time, the flash point is 26.5℃ and 30.5℃ higher than that of 25# naphthenic mineral oil respectively, which indicates that the binary hydrocarbon insulating liquid of the present application has better high temperature resistance. In addition, the biodegradation rate of the binary hydrocarbon insulating liquid of examples 1 and 2 is much higher than that of 25# naphthenic mineral oil, which indicates that the binary hydrocarbon insulating liquid of the present application has outstanding advantages in environmental protection performance. The binary hydrocarbon insulating liquid of example 3 has other performance indicators better than 25# naphthenic mineral oil except that the kinematic viscosity is slightly higher than that of 25# naphthenic mineral oil.

[0127] As can be seen from Table 3, although Comparative Examples 1-3 exhibit excellent biodegradation rates of 86%-95%, their lightning impulse breakdown voltages are significantly low, being 170.43 kV / 10 mm-172.45 kV / 10 mm, far lower than the performance levels of Examples 1-3, i.e. 174.86 kV / 10 mm-173.02 kV / 10 mm.

[0128] The fundamental reason for this phenomenon is the change in molecular level mechanism when the ratio deviates from the optimal range:

[0129] When the volume percentage of short-chain low-branched alkanes exceeds 30%, the volume percentage of short-chain low-branched alkanes in Comparative Example 1 is 40%, the volume percentage of short-chain low-branched alkanes in Comparative Example 2 is 80%, and the volume percentage of short-chain low-branched alkanes in Comparative Example 3 is 90%. Although the high ionization energy characteristics of short-chain low-branched alkanes are more fully utilized, theoretically, higher lightning impulse insulation performance should be obtained, but in fact, abnormal performance decline occurs. The mechanism of this abnormal phenomenon is that a high proportion of short-chain molecules disrupts the molecular synergistic balance of the complex system: first, an excessive amount of short-chain low-branched alkanes leads to an insufficient proportion of long-chain multi-branched alkanes in the system, which cannot form an effective molecular entanglement network and steric shielding structure, resulting in a lack of sufficient structural stability under strong electric field impact; second, the interaction between short-chain low-branched alkanes is relatively weak, and when aggregated at a high concentration, it is easy to undergo local rearrangement and phase separation under the action of an electric field, forming micro-inhomogeneous regions, which become electric field concentration points, thereby reducing the overall breakdown strength; third, a high proportion of short-chain low-branched alkanes significantly reduces the viscosity and intermolecular cohesion of the system, although it is beneficial to biodegradation, with a degradation rate of 86%-95%, but under the condition of transient high stress of lightning impulse, low cohesion makes it difficult for molecules to form an effective stress transfer and energy dissipation mechanism, resulting in the accumulation of impact energy in local areas and the initiation of breakdown.

[0130] Further mechanism analysis shows that the key to the excellent impact insulation performance and good biodegradation rate of the compositions of embodiments 1-3 is that the volume percentage of short-chain low-branched alkanes in the range of 10-30% achieves the precise balance between the electrical synergistic effect and the degradation synergistic effect. In terms of electrical synergism, the appropriate amount of short-chain low-branched alkanes provides a high ionization energy basis, while sufficient long-chain multi-branched alkanes ensure the structural integrity of the molecular network, and the two synergistically form a dual protection mechanism of high ionization energy and stable structure. In terms of degradation synergism, the high degradation activity of short-chain low-branched alkanes combined with the multi-branched structure of long-chain multi-branched alkanes ensures sufficient enzyme attack sites and avoids structural instability caused by excessive degradation. Comparative examples 1-3, due to the imbalance of the ratio, although they may perform outstandingly in a single performance indicator, such as high degradation rate, they lose the multiple synergistic effects and cannot maintain stable comprehensive performance in the complex application environment of electrical equipment, which fully proves the scientificity of the molecular design principle and the accuracy requirement of the ratio control of the present application.

[0131] Therefore, the binary hydrocarbon insulating liquid with high insulation resistance and strong impact insulation provided by the present application can be a good substitute for mineral oil and has a good application prospect in high-voltage and large-capacity electrical equipment.

[0132] Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0133] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A binary compound hydrocarbon insulating liquid, characterized in that, It consists of the following components by volume percentage: Short-chain, low-branched alkanes comprise 10%–30%; the remainder are long-chain, multi-branched alkanes, totaling 100%. In short-chain, low-branched alkanes, the number of carbon atoms in the first main chain is 15 to 20, the number of first branches is 1 to 2, the first branch is methyl and / or ethyl, and the first branch is distributed at the end of the first main chain; In long-chain branched alkanes, the number of carbon atoms in the second main chain is 21 to 25, the number of second branches is 2 to 6, and the second branches are methyl and / or ethyl.

2. The binary compound hydrocarbon insulating liquid according to claim 1, characterized in that, It consists of the following components by volume percentage: Short-chain, low-branched alkanes comprise 20%–30%; the remainder are long-chain, multi-branched alkanes, totaling 100%.

3. The binary compound hydrocarbon insulating liquid according to claim 1, characterized in that, In short-chain, low-branched alkanes, the first main chain has 18 carbon atoms and the first branch has 1.

4. The binary compound hydrocarbon insulating liquid according to claim 1, characterized in that, In long-chain branched alkanes, the number of second branches is 3.

5. The binary compound hydrocarbon insulating liquid according to claim 1, characterized in that, The structural formulas of short-chain, low-branched alkanes are shown below: 。 6. The binary compound hydrocarbon insulating liquid according to claim 1, characterized in that, The structural formulas of long-chain branched alkanes are shown below: 。 7. A method for preparing a binary composite hydrocarbon insulating liquid according to any one of claims 1 to 6, characterized in that, Includes the following steps: Short-chain low-branched alkanes and long-chain multi-branched alkanes are mixed evenly, filtered and dried to obtain a binary compound hydrocarbon insulating liquid.

8. The application of the binary compound hydrocarbon insulating liquid according to any one of claims 1 to 6 in an oil-immersed transformer.

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