Insulating oil paper for inhibiting interfacial charge accumulation under DC stress and preparation method thereof

Abstract

The invention discloses an insulating oil paper for inhibiting interfacial charge accumulation under direct current stress and a preparation method thereof. A 3-amino-1,2,4-triazole additive is added to a mineral insulating oil, and electromagnetic stirring is performed under heating conditions until the 3-amino-1,2,4-triazole additive is uniformly distributed in the mineral insulating oil. Vacuum drying operations are performed on cellulose insulating paper and mineral insulating oil containing the 3-amino-1,2,4-triazole additive respectively, and the cellulose insulating paper is immersed in the insulating oil to ensure that the insulating oil in the cellulose insulating paper is fully saturated. Vacuum drying is performed again to obtain the oil paper containing the 3-amino-1,2,4-triazole additive. The 3-amino-1,2,4-triazole molecules form stable hydrogen bonds with the cellulose molecules, and the portion of the insulating paper surface to which the 3-amino-1,2,4-triazole molecules are attached has a tendency to attract positive polarity particles in the oil, thereby changing the charge distribution of the double electric layer, reducing the charge accumulation between the oil paper and the paper, thereby reducing the interface potential barrier caused by the double electric layer, and reducing the charge accumulation at the oil-paper interface under direct current stress.

Description

Technical Field

[0001] The invention relates to the technical field of oil-paper insulation of converter transformers, in particular to insulating oil paper capable of suppressing interfacial charge accumulation under direct current stress and a preparation method thereof. Background Art

[0002] In the primary equipment investment of UHV DC transmission projects, converter transformers account for the highest proportion, reaching 40%-50%. Converter transformers are core node equipment connecting AC systems and DC systems, and their reliability directly affects the safety and stability of the entire transmission system. The insulation design and manufacturing of converter transformers are one of the core issues restricting the development of DC transmission equipment in my country. The cost of returning a UHV converter transformer to the factory for repair due to a discharge breakdown failure is about 5 to 8 million yuan per unit. If, in extreme cases, an insulation discharge failure causes arcing and explosion, the loss will be as high as tens of millions or even hundreds of millions of yuan. Therefore, it is urgent to improve the insulation design and manufacturing level of converter transformers and further master the core technology of manufacturing major UHV transmission equipment.

[0003] Converter transformers mostly use an oil-paper composite insulation structure consisting of overlapping insulating paperboard and insulating oil gaps, with a large number of oil-paper interfaces. Traditional studies on internal space charge in uniform materials often require a high electric field to observe obvious charge accumulation, but the oil-paper interface still has obvious charge accumulation under a lower working electric field, which distorts the local electric field and causes surface flashover or insulation failure. Therefore, the oil-paper interface becomes an insulation weak point. Traditional dielectric polarization theory believes that the interface charge of composite insulating media follows the Maxwell-Wagner-Sillar (MWS) polarization model, that is, the interface charge accumulation comes from the discontinuity of the ratio of the conductivity to the dielectric constant of the insulating materials on both sides of the interface. However, a large number of studies have shown that the oil-paper interface charge does not follow the MWS polarization model. Due to the scattering effect of the double electric layer, there is an additional potential barrier at the oil-paper interface that hinders charge transport, resulting in a large amount of charge accumulation at the oil-paper interface. The increase in the amount of interface charge caused by the double electric layer at the oil-paper interface will make the degree of electric field distortion more serious, posing a hidden danger to the reliability of the oil-paper insulation system. Summary of the invention

[0004] The present invention aims to provide an insulating oil paper and a preparation method for suppressing interfacial charge accumulation under DC stress, so as to overcome the problems of surface flashover and insulation failure caused by the increase of interfacial charge accumulation caused by the double electric layer at the oil-paper interface in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing insulating oil paper for inhibiting interfacial charge accumulation under DC stress,

[0007] Adding 3-amino-1,2,4-triazole additive to insulating oil under heating conditions and stirring until uniform to obtain insulating oil containing 3-amino-1,2,4-triazole additive;

[0008] The insulating paper and the insulating oil containing 3-amino-1,2,4-triazole additive are dried separately;

[0009] The insulating paper is immersed in insulating oil containing 3-amino-1,2,4-triazole additive, and the oil paper containing 3-amino-1,2,4-triazole additive is prepared after drying.

[0010] Preferably, the concentration of the 3-amino-1,2,4-triazole additive in the insulating oil is 10 ppm.

[0011] Preferably, the heating is carried out in a water bath at a temperature of 60-80°C.

[0012] Preferably, the stirring is performed by electromagnetic stirring, and the electromagnetic stirring time is 10-15 hours.

[0013] Preferably, the drying is performed by vacuum drying.

[0014] Preferably, the vacuum drying temperature is 80-100° C., and the vacuum drying time is 24-36 hours.

[0015] Preferably, the insulation paper is cellulose insulation paper.

[0016] Preferably, the insulating oil is mineral insulating oil.

[0017] Preferably, the mass ratio of the insulating oil containing 3-amino-1,2,4-triazole additive to the insulating paper is 5:1.

[0018] The invention discloses an insulating oil paper for inhibiting the accumulation of interfacial charge under direct current stress, and the insulating oil paper containing 3-amino-1,2,4-triazole additive is prepared by a method for preparing insulating oil paper for inhibiting the accumulation of interfacial charge under direct current stress.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides a method for preparing insulating oil paper that inhibits interfacial charge accumulation under DC stress, wherein a 3-amino-1,2,4-triazole additive is added to mineral insulating oil, electromagnetic stirring is performed under heating conditions, and the 3-amino-1,2,4-triazole additive is stirred until the 3-amino-1,2,4-triazole additive is uniformly distributed in the mineral insulating oil, cellulose insulating paper and the mineral insulating oil containing the 3-amino-1,2,4-triazole additive are vacuum dried respectively, the cellulose insulating paper is immersed in the insulating oil to ensure that the insulating oil in the cellulose insulating paper is fully saturated, and then the cellulose insulating paper is dried again. Vacuum drying is carried out to prepare oil paper containing 3-amino-1,2,4-triazole additive. 3-amino-1,2,4-triazole molecules form stable hydrogen bonds with cellulose molecules. The addition of 3-amino-1,2,4-triazole introduces additional hole traps into the oil-paper insulation system. Therefore, the part of the insulating paper surface attached with 3-amino-1,2,4-triazole molecules has a tendency to attract positive polarity particles in the oil, thereby changing the charge distribution of the double electric layer, reducing the charge accumulation between the oil and paper, and the interfacial potential barrier caused by the double electric layer is reduced, thereby reducing the charge accumulation at the oil-paper interface under DC stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart of a method for preparing insulating oil paper for inhibiting interfacial charge accumulation under DC stress;

[0021] Figure 2 is the PDOS diagram relative to the entire oil-paper system, a is the PDOS diagram of the insulating paper without additional additives, b is the PDOS diagram of the insulating oil without additional additives;

[0022] Figure 3 Schematic diagram of the double-layer charge distribution at the oil-paper interface without additives;

[0023] Figure 4 It is the molecular structure of 3-amino-1,2,4-triazole;

[0024] Figure 5 It is the hydrogen bond between the cellulose molecule and the 3-amino-1,2,4-triazole molecule;

[0025] Figure 6 It is the PDOS diagram of the insulating oil containing 3-amino-1,2,4-triazole additive;

[0026] Figure 7 Schematic diagram of the charge distribution of the double electric layer at the oil-paper interface containing 3-amino-1,2,4-triazole;

[0027] Figure 8Figure 2 is the space charge waveform of oil-impregnated paper-oil structure. a is the oil-paper space charge waveform without additives under +5.1kV DC voltage conditions. b is the oil-paper space charge waveform without additives under -5.1kV DC voltage conditions. c is the oil-paper space charge waveform with 3-amino-1,2,4-triazole additive under +5.1kV DC voltage conditions. d is the oil-paper space charge waveform with 3-amino-1,2,4-triazole additive under -5.1kV DC voltage conditions. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0031] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0032] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0033] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0035] like Figure 1 The present invention provides a method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress, and the steps are as follows:

[0036] S101 adds 3-amino-1,2,4-triazole additive to insulating oil under heating conditions and stirs until uniform to obtain insulating oil containing 3-amino-1,2,4-triazole additive;

[0037] S102 dries the insulating paper and the insulating oil containing 3-amino-1,2,4-triazole additive separately;

[0038] S103: The insulating paper is immersed in the insulating oil containing 3-amino-1,2,4-triazole additive, and the oil paper containing 3-amino-1,2,4-triazole additive is obtained after drying. The concentration of 3-amino-1,2,4-triazole additive in the insulating oil is 10ppm, the heating is carried out by water bath heating, the water bath heating temperature is 60-80℃, the stirring is carried out by electromagnetic stirring, the electromagnetic stirring time is 10-15 hours, the drying is carried out by vacuum drying, the vacuum drying temperature is 80-100℃, the vacuum drying time is 24-36 hours, the insulating paper is cellulose insulating paper, the insulating oil is mineral insulating oil, and the mass ratio of the insulating oil containing 3-amino-1,2,4-triazole additive to the insulating paper is 5:1.

[0039] The specific research process and research results are as follows:

[0040] The present invention regulates the charge distribution of the interfacial double electric layer by material modification to reduce the influence of the interfacial double electric layer. The present invention provides an additive formula suitable for mineral insulating oil and cellulose insulating paper. Adding 10ppm concentration of 3-amino-1,2,4-triazole (triazol-3-amine, ATA) additive can reduce the interfacial charge accumulation in oil-paper insulation under DC stress by 50%. The preparation process of oil-paper containing additive is as follows:

[0041] Add 10ppm ATA additive to mineral insulating oil, and stir electromagnetically for 10 hours under 70℃ water bath heating conditions to ensure uniform distribution of the additive in the mineral insulating oil. Vacuum dry the cellulose insulating paper and the mineral insulating oil containing ATA additive at 80℃ for 24 hours, then immerse the cellulose insulating paper in insulating oil with a mass ratio of 5:1, and vacuum dry it again at 80℃ for 24 hours to ensure that the insulating oil in the cellulose insulating paper is fully saturated, and the ATA molecules form stable hydrogen bonds with the cellulose molecules, thus making the oil-paper sample. Test the micro-water content in the oil of the prepared samples to confirm that the moisture content in the oil of each sample is less than 10ppm.

[0042] According to first-principles calculations, the double-layer charge distribution characteristics at the oil-paper interface originate from the difference in electron affinity between the insulating paper and insulating oil components. The basic component of cellulose insulating paper is cellulose, whose molecules are composed of multiple hydroxyl groups and glycosidic bonds. The oxygen atoms in the hydroxyl and glycosidic groups have strong electronegativity. In the oil-paper sample without any additional additives, the insulating paper surface has a high affinity for the negative polarity particles in the insulating oil. According to Koopmans theorem, the electron affinity can be expressed as the lowest unoccupied molecular orbital energy (E LOMO ) is approximately expressed.

[0043] Figure 2 The density of states (PDOS) of insulating paper and insulating oil without additional additives shows that the E LOMO 20% lower than insulating oil, which means that insulating paper is more likely to become an electron acceptor in the oil-paper insulation system. Figure 3 The double electric layer structure of the oil-paper interface shown in the figure has a narrow negative charge distribution range located on the surface of the insulating paper, with a thickness of the molecular order; the positive charge distribution range is relatively wide and located in the oil layer close to the surface of the insulating paper, which is generally tight inside and loose outside, with a thickness of the micron order.

[0044] Under DC voltage, a large number of carriers excited by the applied voltage migrate under the driving of the electric field. Due to the scattering effect of the double electric layer, there is an additional potential barrier at the oil-paper interface that hinders the charge transport. Therefore, a large amount of charges that migrate to the vicinity of the oil-paper interface accumulate at the interface.

[0045] In order to reduce the charge accumulation at the oil-paper interface and avoid possible local discharge and insulation degradation, the electronic density of states (PDOS) of the oil-paper interface structure was calculated using the PBE functional for additives containing oxygen or nitrogen elements that can form hydrogen bonds with cellulose molecules. The influence of lone pairs of electrons in oxygen and nitrogen elements on the interface potential barrier was studied. It was found that the ATA molecular structure containing multiple nitrogen atoms can form hydrogen bonds with cellulose molecules, easily adhere to the surface of insulating paper composed of cellulose, and adjust the double layer charge distribution at the oil-paper interface to reduce the interface potential barrier.

[0046] Figure 6 The density of states (PDOS) of insulating paper and insulating oil containing ATA additives is shown in Figure 1. It can be seen that the addition of ATA introduces additional hole traps into the oil-paper insulation system. Therefore, the part of the insulating paper surface with ATA molecules attached has a tendency to attract positive polarity particles in the oil, thereby changing the charge distribution of the double layer, such as Figure 7 As shown, the interface barrier caused by the double electrical layer is reduced.

[0047] Using Kunlun Karamay 25# domestic mineral oil and Weidmann ordinary cellulose insulation paper, the charge distribution of the oil-impregnated paper-oil double-layer sample under an applied DC voltage of ±5.1 kV was measured based on the pulsed electro-acoustic (PEA) method. Figure 8 As shown, the abbreviation OP represents an oil-impregnated paper specimen.

[0048] Under applied voltages of different polarities, a large amount of space charge accumulates at the oil-paper interface, with the same polarity as the oil-side electrode. Within 20 minutes, the accumulated oil-paper interface charge in the oil-impregnated paper-oil sample containing ATA additives is reduced by about 55% to 59% compared to the oil-impregnated paper-oil sample without any additional additives.

[0049] Embodiment 1:

[0050] The present invention provides a method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress, the steps are as follows:

[0051] Adding 3-amino-1,2,4-triazole additive to insulating oil under heating conditions and stirring until uniform to obtain insulating oil containing 3-amino-1,2,4-triazole additive;

[0052] The insulating paper and the insulating oil containing 3-amino-1,2,4-triazole additive are dried separately;

[0053] The insulating paper is immersed in the insulating oil containing 3-amino-1,2,4-triazole additive, and the oil paper containing 3-amino-1,2,4-triazole additive is obtained after drying. The concentration of 3-amino-1,2,4-triazole additive in the insulating oil is 10ppm, the heating adopts water bath heating, the water bath heating temperature is 60℃, the stirring adopts electromagnetic stirring, the electromagnetic stirring time is 10 hours, the drying adopts vacuum drying, the vacuum drying temperature is 80℃, the vacuum drying time is 24 hours, the insulating paper adopts cellulose insulating paper, the insulating oil adopts mineral insulating oil, and the mass ratio of the insulating oil containing 3-amino-1,2,4-triazole additive and the insulating paper is 5:1.

[0054] Embodiment 2:

[0055] The present invention provides a method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress, the steps are as follows:

[0056] Adding 3-amino-1,2,4-triazole additive to insulating oil under heating conditions and stirring until uniform to obtain insulating oil containing 3-amino-1,2,4-triazole additive;

[0057] The insulating paper and the insulating oil containing 3-amino-1,2,4-triazole additive are dried separately;

[0058] The insulating paper is immersed in the insulating oil containing 3-amino-1,2,4-triazole additive, and the oil paper containing 3-amino-1,2,4-triazole additive is obtained after drying. The concentration of 3-amino-1,2,4-triazole additive in the insulating oil is 10ppm, the heating adopts water bath heating, the water bath heating temperature is 80℃, the stirring adopts electromagnetic stirring, the electromagnetic stirring time is 15 hours, the drying adopts vacuum drying, the vacuum drying temperature is 100℃, the vacuum drying time is 36 hours, the insulating paper adopts cellulose insulating paper, the insulating oil adopts mineral insulating oil, and the mass ratio of the insulating oil containing 3-amino-1,2,4-triazole additive and the insulating paper is 5:1.

[0059] Embodiment 3:

[0060] The present invention provides a method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress, the steps are as follows:

[0061] Adding 3-amino-1,2,4-triazole additive to insulating oil under heating conditions and stirring until uniform to obtain insulating oil containing 3-amino-1,2,4-triazole additive;

[0062] The insulating paper and the insulating oil containing 3-amino-1,2,4-triazole additive are dried separately;

[0063] The insulating paper is immersed in the insulating oil containing 3-amino-1,2,4-triazole additive, and the oil paper containing 3-amino-1,2,4-triazole additive is obtained after drying. The concentration of 3-amino-1,2,4-triazole additive in the insulating oil is 10ppm, the heating adopts water bath heating, the water bath heating temperature is 70℃, the stirring adopts electromagnetic stirring, the electromagnetic stirring time is 12 hours, the drying adopts vacuum drying, the vacuum drying temperature is 90℃, the vacuum drying time is 30 hours, the insulating paper adopts cellulose insulating paper, the insulating oil adopts mineral insulating oil, and the mass ratio of the insulating oil containing 3-amino-1,2,4-triazole additive and the insulating paper is 5:1.

[0064] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields, and the above-mentioned specific embodiments are only illustrative and instructive, rather than restrictive. Under the guidance of the specification, a person skilled in the art can also make many forms without departing from the scope of protection of the claims of the present invention, all of which belong to the scope of protection of the present invention.

Claims

1. A method for preparing insulating oil paper for inhibiting interfacial charge accumulation under DC stress, characterized in that: Adding 3-amino-1,2,4-triazole additive to insulating oil under heating conditions and stirring until uniform to obtain insulating oil containing 3-amino-1,2,4-triazole additive; The insulating paper and the insulating oil containing 3-amino-1,2,4-triazole additive are dried separately; The insulating paper is immersed in the insulating oil containing the 3-amino-1,2,4-triazole additive, and the insulating paper containing the 3-amino-1,2,4-triazole additive is prepared after drying; The concentration of 3-amino-1,2,4-triazole additive in insulating oil is 10ppm; The insulating paper is cellulose insulating paper; The insulating oil is mineral insulating oil.

2. The method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress according to claim 1, characterized in that: The heating is carried out in a water bath at a temperature of 60-80°C.

3. The method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress according to claim 1, characterized in that: The stirring is carried out by electromagnetic stirring, and the electromagnetic stirring time is 10-15 hours.

4. The method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress according to claim 1, characterized in that: The drying is performed by vacuum drying.

5. The method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress according to claim 4, characterized in that: The vacuum drying temperature is 80-100° C., and the vacuum drying time is 24-36 hours.

6. The method for preparing insulating oil paper for suppressing interfacial charge accumulation under DC stress according to claim 1, characterized in that: The mass ratio of the insulating oil containing the 3-amino-1,2,4-triazole additive to the insulating paper is 5:

1.

7. An insulating oil paper for inhibiting interfacial charge accumulation under DC stress, characterized in that: Oil paper containing 3-amino-1,2,4-triazole additive prepared by the method for preparing insulating oil paper for inhibiting interfacial charge accumulation under DC stress as described in any one of claims 1-6.

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