High-compatibility mixed natural ester insulating oil paper system as well as preparation method and application thereof

Abstract

The invention provides a high-compatibility mixed natural ester insulating oil paper system as well as a preparation method and application thereof. The mixed natural ester insulating oil paper system comprises mixed natural ester insulating oil and insulating paper. The mixed natural ester insulating oil is composed of natural triester and fatty acid methyl ester, and the volume ratio of the natural triester to the fatty acid methyl ester is (80-92): (8-20). The insulation paper is unmodified electrical paper. The mixed natural ester insulating oil paper system embodies high compatibility, can realize an optimal pairing relationship, and solves the problems of data scarcity and model selection uncertainty in the mixed natural ester field in the prior art.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of insulating oil, and particularly relates to a high-compatibility mixed natural ester insulating oil-paper system and a preparation method and application thereof. BACKGROUND

[0002] The transformer oil-paper insulation system is prone to compatibility problems in long-term operation, such as acid generated by oil aging, viscosity rise, breakdown strength drop and the like. At the same time, the electrical and mechanical properties are attenuated due to oil absorption and water content fluctuation of the insulation paper, and the two promote each other to accelerate the life deterioration.

[0003] The existing research mainly focuses on the compatibility evaluation of mineral oil or single natural ester oil and paper materials, and there are scattered conclusions on the performance of different paper types, but the best matching relationship that can be reproduced is still unclear. At present, in order to consider the viscosity-temperature characteristics and environmental protection, mixed natural ester insulating oil is used in industry. However, the compatibility data of mixed natural ester and various papers are obviously insufficient: there is a lack of formula-paper matching conclusions that can be directly selected for engineering under uniform aging conditions, and performance boundaries that can support type acceptance. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a high-compatibility mixed natural ester insulating oil-paper system and a preparation method and application thereof. The mixed natural ester insulating oil-paper system embodies high compatibility, realizes the best matching relationship, and solves the problems of data scarcity and uncertain selection in the field of mixed natural ester in the prior art.

[0005] To achieve this purpose, the present application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a high-compatibility mixed natural ester insulating oil-paper system, comprising: mixed natural ester insulating oil and insulation paper.

[0007] The mixed natural ester insulating oil is composed of natural triester and fatty acid methyl ester, and the volume ratio of the natural triester to the fatty acid methyl ester is (80-92):(8-20).

[0008] The insulation paper is unmodified electrical paper.

[0009] Preferably, the natural triester is rapeseed-based natural ester, and the fatty acid methyl ester is rapeseed methyl ester.

[0010] Preferably, the unmodified electrical paper is selected from any one or more of laminated paper, crepe paper, ordinary electrical paper or white shell paper.

[0011] Preferably, the volume ratio of the natural triester to the fatty acid methyl ester is (88-92):(8-12).

[0012] Preferably, the mixed natural ester insulating oil has a water content of ≤100 mg / kg, and the mass water content of the insulating paper is ≤0.5%.

[0013] In a second aspect, the present application provides a preparation method of the mixed natural ester insulating oil-paper system with high compatibility, comprising the following steps:

[0014] S1: providing a mixed natural ester insulating oil;

[0015] S2: mixing the insulating paper with the mixed natural ester insulating oil, and obtaining the mixed natural ester insulating oil-paper system.

[0016] Preferably, the mixed natural ester insulating oil is obtained by mixing the filtered and dried natural tri-ester with fatty acid methyl ester.

[0017] Preferably, the mixing is performed under stirring, and the stirring speed is 700-900 rpm.

[0018] Preferably, the mixing is further followed by ultrasonic dispersion, and the ultrasonic dispersion is performed for 3-6 times, and each time is not less than 20 min.

[0019] Preferably, in step S2, the mass ratio of the insulating paper to the mixed natural ester insulating oil is 1:(18-22).

[0020] Preferably, the mixing in step S2 is performed for 20-30 h.

[0021] In a third aspect, the present application provides an application of the mixed natural ester insulating oil-paper system with high compatibility in an oil-immersed transformer.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The present application provides a mixed natural ester insulating oil-paper system with high compatibility, and the system does not need to add any additives or modify any materials, and the compatibility is obviously improved by matching the oil-paper structure, the compatibility difference between the mixed oil and different paper types is determined, and the best oil-paper combination is selected and determined, so as to solve the problems of data scarcity and uncertain selection in the field of mixed natural ester in the prior art. According to tests, the mixed natural ester insulating oil-paper system provided by the present application meets the standards required by DL / T1811-2018 and QB / T 4250-2011 in terms of the dielectric loss factor, breakdown voltage, and tensile properties of the insulating paper before and after aging. Therefore, the mixed natural ester insulating oil-paper system provided by the present application can improve the compatibility and also meet the insulation performance well.

[0024] Meanwhile, the step of preparing the mixed natural ester insulating oil-paper system is simple, and the process does not need special treatment, which is beneficial to realize mass production and stock equipment modification. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0026] Based on the problems of insufficient compatibility of the insulating oil-paper in the oil-immersed transformer in the prior art and insufficient compatibility data of the mixed natural ester and various papers, the present application provides a mixed natural ester insulating oil-paper system with high compatibility under the premise of no modification, which comprises a mixed natural ester insulating oil and insulating paper, and gives performance limits that can be used for type acceptance, to solve the problems of compatibility and type selection uncertainty in the application of the mixed natural ester.

[0027] In the present application, the mixed natural ester insulating oil is composed of natural triesters and fatty acid methyl esters, wherein the natural triesters are preferably rapeseed-based natural esters (abbreviation: RA); and the fatty acid methyl esters are rapeseed methyl esters (abbreviation: RME). The present application preferably uses natural triesters and fatty acid methyl esters to compose the mixed natural ester insulating oil, because the addition of the fatty acid methyl esters can reduce the viscosity of the system, improve the flowability, and at the same time maintain good dielectric properties, so as to improve the overall compatibility and thermal stability. Further, RA and RME are preferred, because the molecular structures of the rapeseed-based natural esters and the rapeseed methyl esters are similar, and the polarity matching degree is high, so that stable oil phase uniformity and low viscosity-temperature index can be obtained.

[0028] In some embodiments of the present application, the volume ratio of the natural triester to fatty acid methyl ester is (80~92):(8~20). That is, the volume content of RME in the mixed natural ester insulating oil is 8~20%, not 0%, such as 8%, 9%, 10%, 12%, 14%, 16%, 18% or 20%, etc. It has been tested that, with the proportion of RME in the mixed natural ester insulating oil increasing from 0% to 20%, the kinematic viscosity of the binary mixed natural ester insulating oil decreases linearly, the acid value and the dielectric loss factor first decrease and then increase, and the power frequency breakdown voltage gradually decreases. It has been tested that, when the volume proportion of RME in the mixed natural ester insulating oil gradually increases from 8% to 14%, the kinematic viscosity of the system shows a downward trend, the acid value and the dielectric loss factor slightly increase, and the power frequency breakdown voltage remains good. Among them, the breakdown voltage of pure RA (0% RME, Comparative Example 1) decreases from 75.0 kV to 70.1 kV, with a retention rate of about 93.5%; when the volume proportion of RME is 10% (Example 2), the breakdown voltage decreases from 75.0 kV to 72.8 kV, with a retention rate of about 97.0%, showing the best performance. At the same time, the kinematic viscosity decreases from 32.0 mm² / s (Comparative Example 1) to 28.5 mm² / s (Example 2), with a decrease of about 10.9%, which is the smallest or the second smallest among all samples. In combination with the performance indicators such as kinematic viscosity, acid value, dielectric loss factor and breakdown voltage retention rate, it is determined by the present application that, when the volume proportion of RME is about 10% (i.e. RA:RME=90:10), the comprehensive performance of the mixed natural ester insulating oil system is the best. Therefore, in combination, the present application most preferably selects the volume proportion of RME to be 10%. That is, the present application most preferably selects the oil ratio RA:RME=90:10.

[0029] In the present application, the insulating paper is unmodified electrical paper, which can be specifically selected from any one or more of laminated paper, crepe paper, ordinary electrical paper or white shell paper.

[0030] It should be noted that, in the present application, the insulating paper is most preferably laminated paper, because the pore size distribution of the paper body of laminated paper is more uniform, the density and thickness tolerance are smaller, the interface is more continuous after oil immersion, and the void and micro-tip defects are fewer, thereby reducing the local electric field distortion and the probability of partial discharge. In addition, the oil absorption amount is moderate, the thickness expansion amount is low, the water content fluctuation is small in the heat-humidity cycle, which is conducive to inhibiting the hydrolysis chain breakage of cellulose of the laminated paper, and thus the decrease amplitude of the electrical strength and the tensile strength is lower. When the paper is combined with the preferred oil ratio RA:RME=90:10 of the present application, the matching degree of the polarity and wettability of the laminated paper and the oil phase is the highest, the paper side has the relatively lowest decrease amplitude, the breakdown voltage decreases by about 4.3%, and the tensile strength decreases by about 4.9%, which is most easily met and superior to the "property box" threshold under the unified aging conditions.

[0031] The application also provides a preparation method of a high-compatibility mixed natural ester insulating oil-paper system, comprising the following steps:

[0032] S1: providing mixed natural ester insulating oil;

[0033] S2: mixing the insulating paper with the mixed natural ester insulating oil, and obtaining the mixed natural ester insulating oil-paper system.

[0034] According to the application, first, mixed natural ester insulating oil is provided.

[0035] In the application, the mixed natural ester insulating oil is obtained by mixing filtered and dried natural tri-ester and fatty acid methyl ester. In some embodiments of the application, RA and RME that have been filtered and vacuum dried are mixed to obtain mixed natural ester insulating oil. The filtering temperature is 55±5℃, preferably 55±2℃; the time is 30±5 min, preferably 30±3 min. The drying is vacuum drying, the drying temperature is 90±5℃, preferably 90±2℃; the pressure is 60±10 Pa, preferably 60±6 Pa; the time is 24-48 h, preferably 30-36 h.

[0036] Specifically, in some embodiments of the application, the above mixing is preferably carried out under the conditions of magnetic stirring and ultrasonic dispersion in sequence. The stirring temperature is 40±5℃, preferably 40±1℃, the speed is 800±100 rpm, preferably 800±40 rpm; the time is 30±5 min, preferably 30±3 min. The ultrasonic dispersion is performed for 3-6 times, such as 3 times, 4 times, 5 times or 6 times; the time of single ultrasonic is not less than 20 min, such as 20 min, 30 min, 40 min or 50 min, etc. In some preferred embodiments of the application, after the above ultrasonic dispersion is completed, the obtained mixed natural ester insulating oil is preferably dried again, the drying is vacuum drying, the temperature is 90±5℃, preferably 90±2℃; the pressure is 60±10 Pa, preferably 60±6 Pa; the time is 24-48 h, preferably 30-36 h.

[0037] After obtaining the mixed natural ester insulating oil, according to the application, the insulating paper is mixed with the mixed natural ester insulating oil, preferably the insulating paper is immersed in the mixed natural ester insulating oil, to obtain the mixed natural ester insulating oil-paper system.

[0038] In some embodiments of the present application, the dried insulation paper is preferably impregnated with the dried mixed natural ester insulating oil at a mass ratio of 1: (18-22), more preferably 1:20 for 20-30 h, preferably 24-28 h, so that the insulation paper is fully impregnated with oil. The drying is vacuum drying, the temperature is 90±5℃, preferably 90±2℃; the pressure is 60±10 Pa, preferably 60±6 Pa; and the time is 24-48 h.

[0039] The mixed natural ester insulating oil paper system obtained after drying described above is in a uniform and transparent state without obvious bubble residues.

[0040] In summary, the preparation method of the high-compatibility mixed natural ester insulating oil paper system provided by the present application is simple in steps, does not require expensive instruments and equipment, is easy to implement, and is convenient for large-scale or industrial production.

[0041] In some embodiments of the present application, the present application uses accelerated aging test to explore the performance of the mixed natural ester insulating oil and the insulation paper in the mixed natural ester insulating oil paper system before and after aging. Before aging, the mixed natural ester insulating oil and the insulation paper need to meet: the water content of the mixed natural ester insulating oil is ≤100 mg / kg, and the mass water content of the insulation paper is ≤0.5%. This is to ensure that the water content in the oil paper system is low, to prevent accelerated hydrolysis reaction and electrical performance degradation, and to improve the comparability and accuracy of the aging test. Through testing, the medium loss factor, breakdown voltage, and insulation paper tensile performance of the high-compatibility mixed natural ester insulating oil paper system provided by the present application all meet the standards required by DL / T 1811-2018 and QB / T 4250-2011. Therefore, the mixed natural ester insulating oil paper provided by the present application can not only improve the compatibility performance, but also can well meet the insulation performance.

[0042] Finally, the present application also provides an application of the above high-compatibility mixed natural ester insulating oil paper system in an oil-immersed transformer.

[0043] In order to further illustrate the present application, the following examples are used for detailed description. The experimental oils used in the following examples of the present application are produced by Zhuoyuan New Material Technology Co., Ltd.

[0044] Example 1

[0045] The present embodiment provides a high-compatibility mixed natural ester insulating oil paper system, and the preparation method thereof is as follows:

[0046] The RA and RME that meet the standards such as IEC 62770 after filtration and vacuum drying treatment are mixed, and the proportion of RME in the mixed oil volume is 8%; and magnetic stirring is carried out, the temperature of the magnetic stirring is set to 40℃, the rotating speed is set to 800 rpm, and the stirring time is set to 30 min. After the magnetic stirring is completed, the mixed oil sample is treated by using an ultrasonic dispersion instrument, the power of the instrument is set to 50 W, the dispersion time is set to 20 min, and after each single dispersion is completed, the oil sample is cooled and then ultrasonic dispersion is carried out again, a total of 3 times of dispersion, 20 min each time, a total of 60 min of dispersion. After the above ultrasonic dispersion is completed, the mixed insulating oil sample is subjected to vacuum drying treatment at 90℃ / 60 Pa for 48 h. After the vacuum drying is completed, the power is turned off, and after being cooled to room temperature (25±2℃), it is taken out, and the mixed natural ester insulating oil is obtained.

[0047] The laminated paper is cut into a size of 5*5 cm, and vacuum drying treatment is carried out for 48 h, the drying temperature is 90℃, and the pressure is 60 Pa. The dried insulating paper is immersed in the dried mixed natural ester insulating oil at a mass ratio of 1:20 (i.e., the mass ratio of the insulating paper to the mixed natural ester insulating oil = 1:20) for 24 h, so that the insulating paper is fully immersed in oil, and a high compatibility mixed natural ester insulating oil paper system is obtained.

[0048] Example 2

[0049] The embodiment provides a preparation method of a high compatibility mixed natural ester insulating oil paper system, which is prepared by referring to the method of Example 1, and the difference from Example 1 is that the proportion of RME in the mixed oil volume is 10%, and the other parameters are unchanged.

[0050] Example 3

[0051] The embodiment provides a preparation method of a high compatibility mixed natural ester insulating oil paper system, which is prepared by referring to the method of Example 1, and the difference from Example 1 is that the proportion of RME in the mixed oil volume is 12%, and the other parameters are unchanged.

[0052] Example 4

[0053] The embodiment provides a preparation method of a high compatibility mixed natural ester insulating oil paper system, which is prepared by referring to the method of Example 1, and the difference from Example 1 is that the proportion of RME in the mixed oil volume is 14%, and the other parameters are unchanged.

[0054] Example 5

[0055] The embodiment provides a preparation method of a high compatibility mixed natural ester insulating oil paper system, which is prepared by referring to the method of Example 2, and the difference from Example 2 is that the insulating paper is selected to be crepe paper, and the other parameters are unchanged.

[0056] Example 6

[0057] This example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system. The method is prepared according to the method of Example 2, and the difference from Example 2 is that the insulating paper is selected as ordinary electrical paper, and other parameters are unchanged.

[0058] Example 7

[0059] This example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system. The method is prepared according to the method of Example 2, and the difference from Example 2 is that the insulating paper is selected as white shell paper, and other parameters are unchanged.

[0060] Comparative Example 1

[0061] This comparative example provides a pure natural ester insulating oil-paper system, and the difference from Example 1 is that RME is not added, and the method is prepared according to the method comprising the following steps:

[0062] The RA is subjected to filtration and vacuum drying treatment, and the specific operation is: first, filter impurities, set the filtration temperature to 55°C, and after the temperature is stable, set the continuous oil filtration time to 30 min; then, vacuum drying treatment is performed, the drying temperature is set to 90°C, the vacuum pressure is set to 60 Pa, and the drying time is 48 h; after the vacuum drying is completed, the power is turned off, and after cooling to room temperature (25±2°C), it is taken out, and a pure RA insulating oil meeting the standards such as IEC 62770 is obtained.

[0063] The laminated paper is cut into a size of 5x5 cm, and vacuum drying treatment is performed for 48 h, and the drying temperature is 90°C and the pressure is 60 Pa. The insulating paper after drying is impregnated in the mixed natural ester insulating oil after drying at a mass ratio of 1:20 for 24 h, so that the insulating paper is fully impregnated with oil, and a pure natural ester insulating oil is obtained.

[0064] Comparative Example 2

[0065] This comparative example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system, and the method is prepared according to the method of Comparative Example 1, and the difference from Comparative Example 1 is that the RA is replaced by pure Karamay 25# mineral oil, and other parameters are unchanged.

[0066] Comparative Example 3

[0067] This comparative example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system, and the method is prepared according to the method of Example 2, and the difference from Example 2 is that the RA is replaced by soybean-based natural ester (volume ratio 90%), and the RME is replaced by soybean oil methyl ester (volume ratio 10%), and other parameters are unchanged.

[0068] Comparative Example 4

[0069] The present comparative example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system, which is prepared by referring to the method of Example 2, and the difference from Example 2 is that RA is replaced by peanut-based natural ester (volume ratio 90%), RME is replaced by peanut oil methyl ester (volume ratio 10%), and other parameters remain unchanged.

[0070] Comparative Example 5

[0071] The present comparative example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system, which is prepared by referring to the method of Example 2, and the difference from Example 2 is that RA is replaced by peanut-based natural ester (volume ratio 90%), RME is replaced by peanut oil methyl ester (volume ratio 10%), and other parameters remain unchanged.

[0072] Comparative Example 6

[0073] The present comparative example provides a preparation method of a high compatibility mixed natural ester insulating oil-paper system, which is prepared by referring to the method of Example 2, and the difference from Example 2 is that RA is replaced by peanut-based natural ester (volume ratio 90%), RME is replaced by peanut oil methyl ester (volume ratio 10%), and other parameters remain unchanged.

[0074] Performance test

[0075] The insulating oil papers prepared in Examples 1-7 and Comparative Examples 1-6 are aged at 130℃ in a closed environment under normal pressure for 168 hours, and the electrical performance of the samples before and after aging is tested, including:

[0076] Oil test: kinematic viscosity at 40℃, dielectric loss factor at 90℃, acid value and power frequency breakdown voltage;

[0077] Paper side: power frequency breakdown voltage, tensile strength, elongation at break and elastic modulus.

[0078] The test method is:

[0079] Kinematic viscosity test at 40℃: the kinematic viscosity of the insulating oil prepared in the examples and comparative examples is tested and compared by using a TP725 kinematic viscosity tester and according to the standard GB / T 265. Before starting the formal test, the oil bath temperature after starting is set to 40℃, and after the temperature rises to 40℃ and stabilizes, 12 mL of the oil sample to be tested is injected into the Ubbelohde viscometer in the equipment, and then the test is started.

[0080] Medium loss factor test at 90℃: The present application uses A1170 full-automatic dielectric loss and resistivity tester and tests and analyzes the dielectric loss factor and volume resistivity of the insulating oil prepared by the examples and the comparative examples at 90℃ according to the standard GB / T 5654-2007. In the specific test process, the test temperature is 90℃, the test frequency is 50 Hz, the electrode distance is 2 mm, the direct current voltage size is set to 500 V, and the voltage amplitude is set to 2 kV.

[0081] Oil side power frequency breakdown voltage detection: The present application uses an intelligent voltage resistance experiment device and tests the power frequency breakdown voltage of the insulating oil prepared by the examples and the comparative examples according to the standard GB / T507-2002. In the specific test process, the voltage rise rate is controlled to be 2 kV / s, the breakdown operation is implemented every 5 min, the total breakdown process is repeated 6 times, and the average value is taken as the final breakdown voltage value.

[0082] Acid value test: The present application uses an automatic potentiometric titrator and tests and compares the acid value of the insulating oil prepared by the examples and the comparative examples according to GB / T 7304 / ASTM D664. Before testing, a potassium hydroxide standard methanol solution (0.1 mol / L) is prepared and calibrated, and a toluene-isopropyl alcohol-anhydrous ethanol mixed solvent is used. 20-50 g of the oil sample is taken into a titration cup, about 100 mL of the solvent is added, a composite indicating electrode is inserted and magnetically stirred, and automatic equivalent point potential titration is carried out at 20-25℃; a blank is deducted synchronously.

[0083] Paper side power frequency breakdown voltage test: The present application uses a power frequency voltage resistance test device and tests the breakdown voltage of the oil-impregnated paper sample according to GB / T 1408.1. The sample is the insulating paper to be tested, which is cut according to the actual thickness, first impregnated with the corresponding oil sample in a vacuum at 90-100℃ for 24 h, and then cooled to room temperature for standby use. In the specific test process, the voltage rise rate is controlled to be 2 kV / s, the breakdown operation is implemented every 5 min, each group has not less than 6 pieces, and the average value is taken as the final breakdown voltage value.

[0084] Tensile strength, elongation at break and elastic modulus test: The present application uses an electronic universal material testing machine and tests the tensile properties of the oil-impregnated paper according to GB / T 12914. The sample is pre-conditioned at 23±1℃, 50±2% RH for 24 h; a test strip with a width of 15 mm and a gauge length of 100 mm is cut along the longitudinal direction (MD) and the transverse direction (CD) respectively, clamped in the clamp, and stretched to break at a constant speed of 20 mm / min.

[0085] The test results before and after aging on the oil side are shown in Table 1, and the test results before and after aging on the paper side are shown in Table 2:

[0086] Table 1

[0087]

[0088] Table 2

[0089]

[0090] The present application sets the "property box" criteria under the unified aging condition (130 °C x 168 h): the oil side needs to meet Δν (i.e., the increment of ν) ≤ 0.20 mm² / s, ΔAN (i.e., the increment of AN) ≤ 0.05 mgKOH / g, BV retention rate ≥ 95%, and the increment of tan δ ≤ 0.10% simultaneously; the paper side needs to meet the decrease of the oil-impregnated paper breakdown voltage and tensile strength each ≤ 8%, the decrease of elongation at break ≤ 10%, and the decrease of elastic modulus ≤ 5% simultaneously.

[0091] The oil side results show that: the four indicators of Example 2 are all optimal and the best in the whole group, specifically Δν = 0.12 mm² / s, ΔAN = 0.038 mgKOH / g, the increment of tan δ = 0.05%, and BV retention rate = 97.0%; Example 1 and Example 3 meet the property box (Δν = 0.19 / 0.18, ΔAN = 0.045 / 0.048, BV retention rate = 95.5% / 95.0%, and the increment of tan δ = 0.07% / 0.08% respectively); Examples 4-7 have at least one of the following out-of-limit conditions: Δν > 0.20, ΔAN > 0.05, or BV < 95%; Comparative Examples 1 and 2 also do not meet the property box (the former has larger Δν, ΔAN, and the increment of tan δ, and the latter has BV retention rate < 95%). Further, Comparative Examples 3-6 (each being a mixed oil with RA:RME = 9:1, laminated paper) all show the same direction degradation on the oil side: among them, Comparative Examples 3-5 have larger increments of viscosity and acid value, accompanied by the increase of dielectric loss and the decrease of breakdown retention rate; although Comparative Example 6 is close to the threshold in some single indicators, Δν and ΔAN still exceed the upper limit of the property box, and the overall does not meet the oil side criteria.

[0092] The paper side results show that: the decrease of the breakdown voltage and tensile strength of Example 2 is 4.3% and 4.9% respectively, which is the lowest in the whole group and meets the property box; the two decreases of Example 1, Example 3, and Examples 5 and 6 are all ≤ 8% and meet the criteria; at least one of the decreases of Example 4, Example 7, and Comparative Examples 1-2 is > 8% and does not meet the criteria. At the same time, Comparative Examples 3-6 generally show greater performance degradation on the paper side: the decrease of the breakdown voltage and tensile strength is close to or exceeds the 8% boundary, reflecting that the impregnation wetting and interface stability are insufficient, and it is difficult to maintain the paper side performance to the property box requirements within the unified aging domain.

[0093] Comprehensive judgment: the group of satisfying the oil side and paper side double-sided property box is example 2, example 1 and example 3, wherein example 2 is lower Δν and ΔAN, higher BV retention rate on the oil side compared with the same paper, different ratio of mixed oil (example 1 and 3), and the paper side also has smaller breakdown voltage and tensile strength reduction; compared with the same oil and different paper (example 5~7), example 2 avoids the out-of-limit of oil side and the excessive reduction of paper side at the same time, which reflects the matching advantage of structure and polarity of the mixed oil with RA:RME=9:1 and laminated paper; compared with all the comparative examples, example 2 has greater safety margin and stability on the oil side and paper side, and the comprehensive compatibility is significantly better.

[0094] Therefore, under the constraint of not modifying the oil and paper, RA:RME=9:1, the fixed pairing of laminated paper significantly better than each control in the unified aging domain satisfies the property box completely, and is determined as the best oil-paper combination of the application.

[0095] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Accordingly, the application is not to be limited to these embodiments shown herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A highly compatible mixed natural ester insulating oil paper system characterized in that, The application relates to a high-compatibility mixed natural ester insulating oil-paper system and a preparation method thereof. The mixed natural ester insulating oil is composed of natural triesters and fatty acid methyl esters, and the volume ratio of the natural triesters to the fatty acid methyl esters is (80-92):(8-20). The insulating paper is unmodified electrical paper. The natural triesters are rapeseed-based natural esters, and the fatty acid methyl esters are rapeseed methyl esters.

2. The highly compatible mixed natural ester insulating oil paper system according to claim 1, characterized in that, The unmodified electrical paper is selected from any one or more of laminated paper, crepe paper, ordinary electrical paper or white shell paper.

3. The highly compatible mixed natural ester insulating oil paper system according to claim 1 or 2, characterized in that, The volume ratio of the natural triesters to the fatty acid methyl esters is (88-92):(8-12).

4. The highly compatible mixed natural ester insulating oil paper system according to any one of claims 1 to 3, characterized in that, The water content of the mixed natural ester insulating oil is less than or equal to 100 mg / kg, and the mass water content of the insulating paper is less than or equal to 0.5%.

5. The highly compatible mixed natural ester insulating oil paper system according to any one of claims 1 to 4, characterized in that, The application further relates to a preparation method of the high-compatibility mixed natural ester insulating oil-paper system.

6. A process for the preparation of a highly compatible mixed natural ester insulating oil paper system as claimed in any one of claims 1 to 5, characterized in that, S1: providing mixed natural ester insulating oil; S2: mixing the insulating paper with the mixed natural ester insulating oil. The mixed natural ester insulating oil is obtained by mixing natural triesters and fatty acid methyl esters after filtration and drying; 7. The preparation method according to claim 6, characterized in that, The mixing is carried out under stirring, and the stirring speed is 700-900 rpm. After the mixing is completed, ultrasonic dispersion is further carried out, the ultrasonic dispersion is carried out for 3-6 times, and the time of single ultrasonic dispersion is not less than 20 min.

8. The preparation method according to claim 7, characterized in that, In step S2, the mass ratio of the insulating paper to the mixed natural ester insulating oil is 1:(18-22); 9. The production method according to any one of claims 6 to 8, characterized by, The mixing time in step S2 is 20-30 h.

10. Application of the high-compatibility mixed natural ester insulating oil-paper system according to any one of claims 1-5 or prepared by the preparation method according to any one of claims 6-9 in an oil-immersed transformer. ​

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