High-temperature-resistant and strong-electric-field-action-resistant low-carbon multi-component mixed insulating oil and application thereof

Abstract

The invention discloses low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field action and application, and belongs to the field of liquid insulating dielectric media. 5 to 10 vol.% of soybean oil; %, 5 to 15 vol.% of PFAE; %, 10 to 25 vol.% of isooctyl stearate; and 0.2 to 5.0 wt% of an antioxidant. Main performance parameters of the electrical insulating liquid meet relevant parameter requirements of GB 2536-2011 unused mineral insulating oil for electrical fluid transformers and switches, and the electrical insulating liquid is particularly suitable for electrical insulating liquid for oil-immersed transformers. Compared with mineral oil, pure natural ester, synthetic ester and the like in the prior art, the multi-element mixed insulating oil disclosed by the invention is lower in acid value, kinematic viscosity and dielectric loss, higher in power frequency breakdown voltage, lightning impulse breakdown voltage and flash point, more excellent in environmental protection performance, lower in cost and beneficial to application.

Description

Technical Field

[0001] The present invention relates to the research and development of a new type of liquid insulating dielectric and its application in electrical equipment, and is particularly suitable for electrical insulating liquids for oil-immersed transformers, and more particularly to a low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field and its application. Background Art

[0002] Power transformers are the core equipment of power grids, and insulating oil is the "heart" of transformers. Insulating oil with excellent performance is essential to ensure the safe and stable operation of transformers. Among the more than 17 million transformers in operation in power grids, mineral oil transformers account for more than 90%. Traditional mineral oil transformers have been used in power grids for more than a hundred years. Their mineral oil-paper insulation system has poor thermal stability, is prone to aging, and has a low explosion temperature point, which seriously restricts the safe operation level of transformers and their service life, and does not meet the "dual carbon" goals and the development needs of future green power grids.

[0003] In recent years, domestic and foreign research on the replacement of mineral insulating oil has mainly focused on natural esters, synthetic esters, modified esters and mixed insulating oils. Compared with mineral oil, natural esters have good physical, chemical and electrical properties, such as high flash point, green and pollution-free, outstanding performance in renewable, fireproof and environmental protection, and delayed aging of insulating paperboard, but natural esters have disadvantages such as high freezing point, high viscosity, high acid value and dielectric loss, poor oxidation stability and poor lightning impulse breakdown performance, which cannot meet the current national standards for mineral oil oil-paper insulated transformers. Synthetic esters have better comprehensive electrical and other properties, but their viscosity is large and the cost is expensive, and the manufacturing equipment and technical conditions are complex, which also limits their promotion and application. General modified esters are better in electrical properties and viscosity, but poor in fire resistance and oxidation stability. At the same time, the lightning impulse breakdown voltage of ester insulating oil is low, especially under long oil gaps, and it cannot be directly filled into existing mineral oil transformers, and the structure of the transformer needs to be modified.

[0004] Mixed insulating oil can complement the performance advantages of various oil products and is an important direction for the development of new liquid dielectrics. The research on mixed insulating oil originated in 2002. At present, the main performance parameters of traditional binary mixed insulating oil cannot meet the requirements of the current standard GB 2536-2011 "Unused mineral insulating oil for electrical fluid transformers and switches"; while some ternary mixed insulating oil performance parameters meet the requirements of GB2536-2011. However, the existing ternary mixed insulating oil has a low lightning impulse voltage, and its dielectric loss and viscosity still have room for further improvement. Summary of the invention

[0005] In view of this, the present invention provides a low-carbon multi-component mixed insulating oil and its application which is resistant to high temperature and strong electric field. The new insulating oil not only meets the relevant parameter requirements of GB2536-2011, but also has lower kinematic viscosity and dielectric loss, as well as higher lightning impulse breakdown voltage, etc.

[0006] The present invention provides a low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field, comprising the following components:

[0007] 60-75 vol.% mineral oil;

[0008] 5-10 vol.% soybean oil;

[0009] 5-15 vol.% PFAE;

[0010] 10-25 vol.% isooctyl stearate;

[0011] 0.2-5.0 wt% antioxidant.

[0012] In some embodiments of the present invention, the low-carbon multi-component mixed insulating oil comprises the following components:

[0013] 60-65 vol.% mineral oil;

[0014] 8-10 vol.% soybean oil;

[0015] 5-10 vol.% PFAE;

[0016] 15-25 vol.% of isooctyl stearate.

[0017] In some preferred embodiments of the present invention, the low-carbon multi-component mixed insulating oil comprises the following components:

[0018] 60 vol.% mineral oil;

[0019] 10 vol.% soybean oil;

[0020] 10 vol.% PFAE;

[0021] 20 vol.% of isooctyl stearate.

[0022] In some embodiments of the present invention, the acid value of the mineral oil is 0.008-0.01 mg KOH / g, and the dielectric loss is 0.0009-0.005.

[0023] In some embodiments of the present invention, the soybean oil has an acid value of 0.01-0.06 mg KOH / g and a dielectric loss of 0.005-0.04.

[0024] In some embodiments of the present invention, the antioxidant is one or more of T511, T501, L06 and L57.

[0025] In some preferred embodiments of the present invention, the antioxidant consists of 0.2-2.5 wt % of a first antioxidant and 0.2-2.5 wt % of a second antioxidant, the first antioxidant is T511 and / or T501, and the second antioxidant is L06 and / or L57.

[0026] In some embodiments of the present invention, the acid value of the low-carbon multi-component mixed insulating oil is not greater than 0.01 mgKOH / g, and the kinematic viscosity is not greater than 12 mm 2 / s.

[0027] In some embodiments of the present invention, the lightning impulse breakdown voltage of the low-carbon multi-component mixed insulating oil at a gap of 25-65 mm is above 203 kV.

[0028] The embodiment of the present invention provides the use of the aforementioned low-carbon multi-component mixed insulating oil in a transformer and / or a switch.

[0029] The embodiment of the present invention provides a low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field. The realization process of the multi-component mixed insulating oil includes: constructing a microscopic physical property parameter matrix characterizing the impact discharge and thermal stability of the oil; calculating and solving the microscopic physical property parameters of different types of oil molecules under the action of electric field and thermal field; preferably determining the oil components resistant to high temperature and strong electric field; determining the proportion of oil components in the insulating oil resistant to high temperature and strong electric field. In the formula of the new insulating oil, the base oil component ranges from 60-75vol.% of mineral oil + 5-10vol.% of soybean oil + 5-15vol.% of PFAE + 10-25vol.% of isooctyl stearate; and the type of antioxidant is preferably selected from T511 or T501, and one from L06 or L57, and the mass concentration of each antioxidant added is the same, which can be 0.2wt%-2.5wt%.

[0030] The low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field described in the present invention can take into account the main advantages of mineral oil, natural ester, modified natural ester and synthetic ester, and its main performance parameters meet the relevant parameter requirements of GB 2536-2011 "Unused mineral insulating oil for electrical fluid transformers and switches". Compared with mineral oil, the multi-component mixed insulating oil has a high flash point, low kinematic viscosity, high power frequency breakdown voltage and excellent environmental performance; compared with pure natural ester, the multi-component mixed insulating oil has low viscosity, dielectric loss and acid value, and higher lightning impulse breakdown voltage; compared with synthetic ester, the multi-component mixed insulating oil has lower acid value, dielectric loss and cost. Compared with existing binary mixed insulating oil and ternary mixed insulating oil, the multi-component mixed insulating oil of the present invention has lower acid value, kinematic viscosity and dielectric loss, higher power frequency breakdown voltage, lightning impulse breakdown voltage and flash point, better environmental performance, and is conducive to application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the lightning impulse breakdown voltage of each base oil under negative polarity at a gap of 25 mm in Example 1;

[0032] Figure 2 is the lightning impulse breakdown voltage of each base oil under negative polarity at a gap of 45 mm in Example 1;

[0033] Figure 3 is the lightning impulse breakdown voltage of each base oil under negative polarity at a gap of 65 mm in Example 1;

[0034] Figure 4 is the average lightning impulse breakdown voltage of the mixture of ester oil and mineral oil in different proportions in Example 1;

[0035] Figure 5 is the thermal conductivity of the multi-component mixed insulating oil and mineral oil in Example 2;

[0036] Figure 6 It is the average lightning impulse breakdown voltage of the multi-component mixed insulating oil, mixed oil, mineral oil and soybean oil under negative polarity in Example 2. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with specific embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0038] The embodiment of the present invention provides a low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field. The formula of the novel insulating oil includes base oil and antioxidant. The base oil composition ranges from 60-75 vol.% of mineral oil, 5-10 vol.% of soybean oil, 5-15 vol.% of PFAE and 10-25 vol.% of isooctyl stearate; the proportion of the antioxidant is 0.2-5.0 wt.%.

[0039] In the embodiments of the present invention, the new insulating oil combines the main advantages of mineral oil and ester oil, and has lower acid value, kinematic viscosity, and dielectric loss than traditional binary mixed insulating oil and ternary mixed insulating oil, and higher power frequency breakdown voltage, lightning impulse breakdown voltage, flash point and environmental protection performance.

[0040] The research and development implementation process of the low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field described in the embodiment of the present invention is as follows: the first step is to construct a microscopic physical property parameter matrix that characterizes the impact discharge and thermal stability performance of the oil; the second step is to calculate and solve the microscopic physical property parameters of different types of oil molecules under the action of electric and thermal fields; the third step is to preferentially determine the oil components resistant to high temperature and strong electric fields; the fourth step is to determine the proportion of oil components in the insulating oil resistant to high temperature and strong electric field impact.

[0041] Step 1: Construct a microscopic physical property parameter matrix to characterize the impact discharge and thermal stability of oil products;

[0042] The ionization energy (IP), electron affinity (EA), and excitation energy (E exa ), energy gap (E gap ), density (ρ), evaporation enthalpy (H), free volume (FFV), and self-diffusion coefficient (D) are taken as characteristic quantities of microscopic physical property parameters, and a two-dimensional four-column characteristic quantity matrix M is constructed.

[0043]

[0044] The first row of the matrix contains the ionization energy (IP), electron affinity (EA), excitation energy (E exa ), energy gap (E gap ) are microscopic electrical parameters, which are the main influencing factors of lightning impulse breakdown characteristics of lightning impulse insulating oil; the density (ρ), evaporation enthalpy (H), free volume (FFV), and self-diffusion coefficient (D) in the second row of the matrix are microscopic thermal parameters, which are the main influencing factors of thermal stability of insulating oil.

[0045] Step 2: Calculate and solve the microscopic physical parameters of different types of oil molecules under the action of electric and thermal fields;

[0046] Materials Studio software was used to construct mineral oils (including chain hydrocarbons, monoalkanes, dialkanes, trialkanes, tetraalkanes and aromatic hydrocarbons), natural esters (including tristearate, tripalmitate, trioleate, trilinoleate and trilinolenate), linoleic acid (C 18:2 ,CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH) and linolenic acid (C 18:3 ,CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH), modified natural ester molecular models (including: methyl ethyl stearate, methyl ethyl palmitate, methyl ethyl oleate, methyl ethyl linoleate and methyl ethyl linolenate). Based on density functional theory, Gaussian software was used to optimize the geometry of the constructed insulating oil molecular model using the M062X functional combined with the 6-311G (d, p) basis set. Electric fields with intensities of 0, 0.002 au, 0.004 au, 0.006 au and 0.008 au were applied to the insulating oil molecular model along the y-axis (1 a.u.=5.1423×10 11 V / m) to obtain the optimal structure of insulating oil molecules under different electric field strengths.

[0047] The energy of neutral molecules, cations and anions of insulating oil is calculated using the M062X functional combined with the 6-311G (d, p) basis set, as shown in equations (1) and (2). The ionization energy of insulating oil molecules is the energy of insulating oil cation molecules minus the energy of insulating oil neutral molecules.

[0048] IP=E M+ -E M (1);

[0049] EA=E M -E M- (2).

[0050] In the formula, E M is the energy calculated when the insulating oil molecule is neutral, E M+ is the energy calculated when the charge of the insulating oil molecule is +1, E M- is the energy calculated when the charge of the insulating oil molecule is -1; the excitation energy and energy gap of the insulating oil molecule are calculated using the M062X functional combined with the 6-311G (d, p) basis set.

[0051] Based on the insulating oil model constructed by Materials Studio software, 50 identical insulating oil molecules were placed in a periodic box with a side length of 10nm using Gromacs software to simulate the microscopic thermal parameters of the insulating oil molecular system. The conjugate gradient method was used to minimize the energy of the insulating oil molecular system and find the lowest energy point of the model. The GAFF (generalAMBER forcefield) force field was used in conjunction with the RESP charge to simulate and analyze the insulating oil molecular system model. First, the model was balanced for 10ns based on the isothermal and isobaric ensemble (NPT ensemble) to make the density of the model more reasonable; then the model was simulated for 10ns based on the canonical ensemble (NVT ensemble), and the obtained trajectory was used to calculate various thermodynamic related properties. The Velocity-rescalef method was used for temperature control, and the Parrinello-rahman method was used for pressure control. The Particle-mesh Ewald method was used to calculate the electrostatic effect, and the truncation method was used to calculate the van der Waals effect. Among them, the temperature is 50℃, 70℃, 90℃, 105℃ and 130℃.

[0052] The total volume of insulating oil is determined by the occupied volume V occ and the free volume V free The free volume fraction of the composition is calculated as shown in formula (3):

[0053]

[0054] The mobility of insulating oil molecules can be characterized by mean square displacement (MSD):

[0055]

[0056] The diffusion coefficient is an important parameter that characterizes the mobility of a substance. The self-diffusion coefficient of insulating oil molecules can be solved with the help of the Einstein formula, as shown in formula (5):

[0057]

[0058] Where a is the fitting slope of the MSD curve. In order to make the calculation result of the self-diffusion coefficient more accurate, 10% to 90% of the MSD curve is selected for linear fitting.

[0059] The evaporation enthalpy of insulating oil molecules can be calculated by formula (6):

[0060] ΔH vap =H(gas)-H(liq)

[0061] =[U(gas)+PVgas ]-[U(liq)+PV liq ]

[0062] ≈[U(gas)+RT]-U(liq)(6);

[0063] = <E pot (gas)>- <E pot (liq)>+RT

[0064] Wherein, H(gas) and H(liq) represent the enthalpy of the molecules in the gas phase and the liquid phase, U(gas) and U(liq) represent the total energy of the molecules in the gas phase and the liquid phase, E(gas) and E(liq) represent the potential energy of the molecules in the gas phase and the liquid phase, P is the pressure, T is the temperature, and R is the molar gas constant.

[0065] Step 3: Select and determine the oil components that are resistant to high temperature and strong electric field impact;

[0066] Based on the calculation of the microscopic electrical parameters and microscopic thermal parameters of insulating oil molecules, the greater the ionization energy, excitation energy and energy gap of the insulating oil molecules, the greater the electron affinity, the smaller the dipole moment, and the better the comprehensive insulation performance. From the perspective of improving the insulating performance of mixed insulating oil, mineral oil molecules, PFAE, diisotridecyl adipate and isooctyl stearate can be selected as the base oils for mixed insulating oil. Based on the calculation of the microscopic thermal parameters of insulating oil molecules, the greater the density and evaporation enthalpy of the insulating oil molecules, the smaller the free volume and self-diffusion coefficient, and the stronger its ability to withstand high temperatures. From the perspective of improving the high temperature resistance of mixed insulating oil, soybean oil is selected as one of the base oils for mixed insulating oil.

[0067] Mineral oil is usually extracted from petroleum and contains a large amount of hydrocarbons. Palm oil is squeezed from the palm fruit of the oil palm tree. The PFAE described in the present invention is modified palm oil with an acid value of 0.01 mg KOH / g; while soybean oil is extracted from soybean seeds and has an acid value of 0.06 mg KOH / g.

[0068] According to the IEC 60897 guidelines, the boost method is used to determine the lightning impulse breakdown voltage of the insulating oil. The lightning impulse breakdown test in the embodiment of the present application is preferably carried out under the condition of an oil gap of 65mm and negative polarity; at each oil gap width, the breakdown voltage of the insulating oil is measured 10 times to obtain the average breakdown voltage value. Before each application of voltage, a relaxation time of 1 minute is maintained. Once the insulating oil is broken down, the oil sample is stirred and allowed to stand for 5 minutes. After the insulating oil is broken down ten times, it is replaced with a new sample. In order to maintain consistency, the experiment was carried out at a temperature of 30°C; the lightning impulse breakdown voltage of mineral oil, PFAE, diisotridecyl adipate, isooctyl stearate and soybean oil under negative polarity was mainly tested at a gap of 25-65mm.

[0069] According to GB / T 261-2021 standard, the closed cup flash points of mineral oil, PFAE, diisotridecyl adipate, isooctyl stearate and soybean oil are 135°C, 210°C, 184°C, 202°C and 326°C respectively. Finally, mineral oil, soybean oil, PFAE and isooctyl stearate are selected as the base oils for the mixed insulating oil.

[0070] Step 4: Determine the proportion of oil components in the insulating oil that is resistant to high temperature and strong electric field impact;

[0071] On the premise that dielectric loss and acid value meet the standards, the flash point and lightning impulse breakdown voltage of the multi-component mixed insulating oil are maximized. The main process of this link is as follows:

[0072] (1) Key performance parameter test of base oil: Mineral oil has the lowest acid value, followed by PFAE and 2-ethylhexyl stearate, and soybean oil has the highest acid value; Mineral oil has the lowest dielectric loss, followed by PFAE and 2-ethylhexyl stearate, and soybean oil has the highest dielectric loss. Comparing the dielectric loss and acid value of base oil with the requirements of GB 2536-2011 standard, the acid value and dielectric loss of soybean oil are much higher than the standard of mineral oil. Therefore, the proportion of mineral oil in multi-component mixed insulating oil should be controlled at 60vol.%-75vol.%.

[0073] (2) Lightning impulse test after ester insulating oil is mixed with mineral oil; In order to ensure that the basic performance of the multi-component mixed insulating oil meets the mineral oil standard and the lightning impulse breakdown characteristics are improved to a certain extent compared with soybean oil, the main oil of the multi-component mixed insulating oil is mineral oil. Furthermore, the negative polarity lightning impulse breakdown voltage of the insulating oil mixed with soybean oil, PFAE and isooctyl stearate and mineral oil was tested, with a gap of 65mm, and the test method was consistent with the above. Compared with the change in lightning impulse breakdown voltage after the mixture of soybean oil and mineral oil, the decrease in lightning impulse of the insulating oil mixed with PFAE and isooctyl stearate and mineral oil was relatively small; the soybean oil in the multi-component mixed insulating oil has a significant reducing effect on its lightning impulse breakdown voltage. Therefore, in order to make the lightning impulse breakdown voltage of the multi-component mixed insulating oil higher than 200kV under the condition of 65mm gap and negative polarity, the proportion of soybean oil should be controlled at 5vol.%-10vol.%.

[0074] In an embodiment of the present invention, the base oil includes 60-75 vol.% of mineral oil, further preferably 60-65 vol.%, more preferably 60 vol.%; preferably, the proportion of the mineral oil is reduced to 60%, which better meets the requirements of green environmental protection, that is, relative to the formula with a proportion of 75 vol.% of mineral oil, the preferred formula of 60-65 vol.% of mineral oil is more low-carbon and environmentally friendly. The acid value of the mineral oil can be 0.008-0.01 mg KOH / g, and the dielectric loss is 0.0009-0.005.

[0075] In addition, the base oil of the embodiment of the present invention comprises: 5-15 vol.% soybean oil, 5-15 vol.% PFAE and 10-25 vol.% isooctyl stearate. Preferably, the soybean oil is 8-10 vol.%, further 10 vol.%; the acid value of the soybean oil is 0.01-0.06 mg KOH / g, and the dielectric loss is 0.005-0.04. The PFAE is preferably 5-10 vol.%, further 10 vol.%; the isooctyl stearate is preferably 15-25 vol.%, more preferably 15-23 vol.%, further 20 vol.%.

[0076] In the embodiment of the present invention, different insulating oils and mineral oils are first mixed in different proportions to determine the ratio range of mineral oil and soybean oil, and then PFAE and isooctyl stearate are added to slightly adjust the ratio so that the basic physical and chemical parameters meet the standards.

[0077] (3) Determination of the configuration ratio of the multi-component mixed insulating oil; the multi-component mixed insulation under different ratios was configured, and its acid value, dielectric loss, flash point and lightning impulse breakdown voltage under 65mm gap negative polarity conditions were tested. Finally, the formula range of the multi-component mixed insulating oil was preferably determined as follows: 60vol.% mineral oil + 10vol.% soybean oil + 10vol.% PFAE + 20vol.% isooctyl stearate; the soybean oil ratio was reduced to 10%, but the PFAE ratio was increased to 10%. At the same time, adding 20% ​​of isooctyl stearate selected by the technical method can mainly increase the lightning impulse breakdown voltage.

[0078] In addition, the type of antioxidant is selected from T511 or T501, and one is selected from L06 or L57, and the mass concentration of each antioxidant added is the same, which is 0.2wt%-2.5wt%. The chemical name of antioxidant T511 is 4,4'-methylenebis(2,6-di-tert-butylphenol), etc., and antioxidant T501 is tert-butyl-p-cresol, which plays an antioxidant role in oil. Antioxidant L06 is high-purity alkylated phenyl-α-naphthylamine, and antioxidant L57 is 2,6-butyl liquid diphenylamine; in addition, the antioxidants and base oil components involved in the embodiments of the present invention are all commercially available products. Vol.% is the abbreviation of volume fraction, and wt% is the abbreviation of mass fraction; the mass fraction of the antioxidant is based on the total mass of the base oil.

[0079] The mixed insulating oil described in the embodiment of the present invention is a low-carbon multi-component mixed insulating oil, and its performance parameters meet the current mineral insulating oil standards, the acid value is not more than 0.01 mg KOH / g, and the kinematic viscosity is not more than 12 mm 2 / s. Moreover, the lightning impulse breakdown voltage of the multi-component mixed insulating oil at a gap of 25-65mm is higher than 203kV and can reach 211kV (here, the lightning impulse breakdown voltage is based on the data measured under the pin-plate electrode with a gap of 65mm as an example).

[0080] In order to better understand the technical content of the present invention, the following specific examples are provided to further illustrate the present invention. In the following examples, unless otherwise specified, all are weight ratios; the raw materials used are commercially available and conventional equipment is used.

[0081] Example 1

[0082] 1. According to the IEC 60897 guidelines, the lightning impulse breakdown voltage of insulating oil is determined by the voltage step-up method. The lightning impulse breakdown tests in this embodiment are all carried out under the condition of 65mm oil gap and negative polarity; the experiment is carried out at a temperature of 30°C. The lightning impulse breakdown voltage of mineral oil, PFAE, diisotridecyl adipate, isooctyl stearate and soybean oil under negative polarity is tested under the gap of 25-65mm. The results are as follows: Figure 1-3 According to GB / T 261-2021 standard, the closed cup flash points of mineral oil, PFAE, diisotridecyl adipate, isooctyl stearate and soybean oil are 135°C, 210°C, 184°C, 202°C and 326°C respectively.

[0083] Table 1 shows the key physical, chemical and electrical parameters of each base oil. Mineral oil has the lowest acid value, followed by PFAE and 2-ethylhexyl stearate, and soybean oil has the highest acid value. Mineral oil has the lowest dielectric loss, followed by PFAE and 2-ethylhexyl stearate, and soybean oil has the highest dielectric loss. Comparing the dielectric loss and acid value of base oils with the requirements of GB 2536-2011, the acid value and dielectric loss of soybean oil are much higher than the standards of mineral oil.

[0084] Table 1 Key physical, chemical and electrical parameters of base oil

[0085]

[0086] The negative polarity lightning impulse breakdown voltage of the insulating oil mixed with soybean oil, PFAE and isooctyl stearate and mineral oil was tested with a gap of 65mm. The test method was the same as above.

[0087] Test results such as Figure 4 , Figure 4 Each curve is a lightning impulse voltage after a mixture of an ester oil and mineral oil in different proportions (soybean oil, isooctyl stearate, and PFAE are all ester oils), and the horizontal axis is the content of the ester oil. Taking the soybean oil + mineral oil curve as an example, when the horizontal axis is 0.2, it means that the volume ratio of the mixed oil at this time is 20% soybean oil + 80% mineral oil. The results show that compared with the change in lightning impulse breakdown voltage after the mixture of soybean oil and mineral oil, the lightning impulse decrease of the insulating oil after PFAE and isooctyl stearate are mixed with mineral oil is relatively small; the soybean oil in the multi-component mixed insulating oil has a significant effect on reducing its lightning impulse breakdown voltage.

[0088] 2. Multicomponent mixed insulating oil (containing antioxidant, with antioxidant addition content of 0.2wt% T511 and 0.2wt% L06) with 4 base oil ratios was configured, and its acid value, dielectric loss, flash point and lightning impulse breakdown voltage under 65mm gap negative polarity conditions were tested. The results are shown in Table 2.

[0089] Table 2 Acid value, dielectric loss, flash point and lightning impulse breakdown voltage of multi-component mixed insulating oil at different proportions

[0090]

[0091] Example 2

[0092] According to the formula, a multi-component mixed insulating oil was prepared, 60 vol.% mineral oil + 10 vol.% soybean oil + 10 vol.% PFAE + 20 vol.% isooctyl stearate, and antioxidants were added, 0.2 wt% T511 + 0.2 wt% L06. In addition, basic performance tests were conducted, and the results are shown in Table 3.

[0093] Table 3 Comparison of performance parameters of insulating oil resistant to high temperature and strong impact field

[0094]

[0095] Note: The formula of ternary mixed insulating oil is 76% mineral oil + 19% soybean oil + 5% PFAE.

[0096] According to Table 3, compared with mineral oil, the acid value of the multi-component mixed insulating oil of the present invention is 0.0046 mgKOH / g lower than that of mineral oil; the power frequency breakdown voltage is 10.9 kV higher, the flash point is 21°C higher, and the insulation and heat resistance are better. Table 3 shows that the multi-component mixed insulating oil of the present invention has outstanding advantages in all aspects compared with mineral oil and mixed insulating oil, and the performance parameters meet the requirements of GB2536-2011, among which the key physical, chemical and electrical properties of the multi-component mixed insulating oil are better than those of mineral oil.

[0097] The present application example refers to the ASTM D7896-2014 "Pressure Differential Scanning Calorimetry (PDSC)" standard to measure the thermal conductivity of multi-component mixed insulating oil and mineral oil. The results are as follows: Figure 5 As shown. With the increase of temperature, the thermal conductivity of multi-component mixed insulating oil and mineral oil shows a linear growth trend. Compared with mineral oil, the thermal conductivity of multi-component mixed insulating oil is higher at any temperature, but the higher the temperature, the smaller the difference in thermal conductivity between the two; when the temperature is 30°C, the thermal conductivity of multi-component mixed insulating oil is 60.12% higher than that of mineral oil, and when the temperature reaches 110°C, the thermal conductivity of multi-component mixed insulating oil is 24.68% higher than that of mineral oil. The operating temperature of the transformer is generally between 40°C and 90°C. In this temperature range, the thermal conductivity of multi-component mixed insulating oil is higher than that of mineral oil, which shows that the heat dissipation capacity of multi-component mixed insulating oil is stronger than that of mineral oil.

[0098] The present invention tests the lightning impulse breakdown voltage of multi-component mixed insulating oil, mineral oil and other typical mixed insulating oils under negative polarity conditions. The results are as follows: Figure 6 As shown in the figure, the formula of the ternary mixed insulating oil is 76% mineral oil, 19% soybean oil and 5% PFAE.

[0099] The results show that under any gap, the average lightning impulse breakdown voltage of the multi-component mixed insulating oil of the present invention is significantly higher than that of the existing binary and ternary mixed insulating oils.

[0100] In addition, the content of ester oil in the multi-component mixed insulating oil of the present invention is between 30% and 40%, and the biodegradation rate is higher than that of the existing binary and ternary mixed insulating oils (the content of ester oil is about 20-25%), and much higher than that of mineral oil. Therefore, the environmental protection performance of the multi-component mixed insulating oil of the present invention has outstanding advantages.

[0101] It can be seen from the above embodiments that the main performance parameters of the multi-component mixed insulating oil described in the embodiments of the present invention meet the relevant parameter requirements of GB2536-2011, and are particularly suitable for electrical insulating liquids for oil-immersed transformers. Compared with the prior art such as mineral oil, pure natural ester, synthetic ester, etc., the multi-component mixed insulating oil of the present invention has lower acid value, kinematic viscosity and dielectric loss, higher power frequency breakdown voltage, lightning impulse breakdown voltage and flash point, better environmental performance, and lower cost, which is conducive to application.

[0102] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0103] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. The above is only a preferred implementation of the present invention. It should be pointed out that due to the limitations of textual expression and the objective existence of infinite specific structures, ordinary technicians in this technical field can make several improvements, modifications or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the inventive concept and technical solution to other occasions without improvement, should be regarded as the protection scope of the present invention.

Claims

1. A low-carbon multi-component mixed insulating oil resistant to high temperature and strong electric field, characterized in that: The composition comprises the following proportions: 60-75 vol.% mineral oil; 5-10 vol.% soybean oil; 5-15 vol.% PFAE; 10-25 vol.% isooctyl stearate; 0.2-5.0 wt% antioxidant.

2. The low-carbon multicomponent mixed insulating oil according to claim 1, characterized in that: The composition comprises the following proportions: 60-65 vol.% mineral oil; 8-10 vol.% soybean oil; 5-10 vol.% PFAE; 15-25 vol.% of isooctyl stearate.

3. The low-carbon multicomponent mixed insulating oil according to claim 2, characterized in that: The composition comprises the following proportions: 60 vol.% mineral oil; 10 vol.% soybean oil; 10 vol.% PFAE; 20 vol.% of isooctyl stearate.

4. The low-carbon multicomponent mixed insulating oil according to any one of claims 1 to 3, characterized in that: The acid value of the mineral oil is 0.008-0.01 mg KOH / g, and the dielectric loss is 0.0009-0.

005.

5. The low-carbon multicomponent mixed insulating oil according to any one of claims 1 to 3, characterized in that: The soybean oil has an acid value of 0.01-0.06 mg KOH / g and a dielectric loss of 0.005-0.

04.

6. The low-carbon multicomponent mixed insulating oil according to any one of claims 1 to 3, characterized in that: The antioxidant is one or more of T511, T501, L06 and L57.

7. The low-carbon multicomponent mixed insulating oil according to claim 6, characterized in that: The antioxidant consists of 0.2-2.5 wt % of a first antioxidant and 0.2-2.5 wt % of a second antioxidant, wherein the first antioxidant is T511 and / or T501, and the second antioxidant is L06 and / or L57.

8. The low-carbon multicomponent mixed insulating oil according to any one of claims 1 to 3, characterized in that: The acid value of the low-carbon multi-component mixed insulating oil is not greater than 0.01 mg KOH / g, and the kinematic viscosity is not greater than 12 mm 2 / s.

9. The low-carbon multicomponent mixed insulating oil according to any one of claims 1 to 3, characterized in that: The lightning impulse breakdown voltage of the low-carbon multi-component mixed insulating oil at a gap of 25-65 mm is above 203 kV.

10. Use of the low-carbon multicomponent mixed insulating oil according to any one of claims 1 to 9 in transformers and / or switches.

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