A potting method for polyurethane resin of a zero-sequence current transformer

Abstract

The present invention discloses a potting method for polyurethane resin of a zero-sequence current transformer. First, resin component A and curing agent component B are fully stirred and mixed in a ratio of 4:1; potting is carried out at the bottom of the housing to form a lower polyurethane resin layer. Then, silicone rubber particles are filled above the lower polyurethane resin layer, and according to the size of the zero-sequence coil, it is placed in the middle of the housing cavity, and then the silicone rubber particles are supplemented and filled, leveled and compacted. Finally, an amine catalyst is fully stirred and mixed with the mixture of resin component A and curing agent component B in a ratio of 2-4 ml / Kg, and potted on the upper surface of the silicone rubber particle filling layer, and then hardened, assembled and tested. Based on the original material of polyurethane resin, the present invention adds a specific catalyst to change the original viscosity performance of the material, and uses the improved polyurethane resin to meet the error requirements of a certain type of transformer under special high and low temperatures, thereby improving the first-pass yield rate of the product, reducing costs and ensuring the construction period.

Description

Technical Field

[0001] The present invention relates to a resin potting method for an instrument transformer, and has an ideal production method for the composite error of a zero-sequence instrument transformer with special low-temperature requirements. Background Art

[0002] In recent years, under the guidance of national policies, wind power generation has been vigorously promoted, and the low-voltage zero-sequence instrument transformers used in its power distribution cabinets have also increased accordingly. Due to the different geographical locations where wind power generation devices are installed, there are significant differences in the ambient temperature, which puts higher requirements on the ambient temperature for the use of instrument transformers. The production of such instrument transformers usually involves placing the coil in a plastic shell and then potting it with polyurethane resin. At present, the ambient temperature requirements for the zero-sequence instrument transformers we produce and process are -45 to +80 °C, with a large temperature difference. If produced by conventional processes and directly potted with polyurethane resin, the iron core inside the zero-sequence instrument transformer will be deformed due to the shrinkage during the curing process of the polyurethane resin, resulting in unqualified product errors or performance, increasing the product manufacturing cost and unable to guarantee the construction period. Summary of the Invention

[0003] The purpose of the present invention is to provide a new polyurethane resin potting method, which can effectively meet the special high and low temperature requirements of customers for the ambient temperature of zero-sequence instrument transformers and ensure the production qualification rate of products.

[0004] The technical solution adopted by the present invention is a potting method for polyurethane resin of a zero-sequence instrument transformer, including the following steps:

[0005] Step 1: Thoroughly stir and mix resin component A and curing agent component B in a ratio of 4:1 and perform vacuum degassing;

[0006] Step 2: Pot the bottom of the housing with the above mixture to form a lower polyurethane resin layer, cure it, and set it aside for use;

[0007] Step 3: Fill silicone rubber particles above the lower polyurethane resin layer, make them located in the middle of the housing cavity according to the size of the zero-sequence coil, and then supplement and fill the silicone rubber particles, level and compact them;

[0008] Step 4: Thoroughly stir and mix amine catalyst with the mixture of resin component A and curing agent component B in a ratio of 2 - 4 ml / Kg, perform vacuum degassing, and then let it stand for 15 - 25 minutes;

[0009] Step 5: Pot the above mixture on the upper surface of the silicone rubber particle filling layer, observe whether there is seepage of the mixture. If there is seepage, continue to let it stand for a period of time; if there is no seepage, the entire rubber particle surface can be potted, and the distance from the potted surface to the top of the housing is controlled at 5 - 8 mm;

[0010] Step 6: When the cover to be potted hardens, use a mixture of resin component A and curing agent component B in a ratio of 4:1 to pot the remaining part and perform defoaming treatment to ensure that the polyurethane resin surface is flat, bright, bubble-free and pitted;

[0011] Step 7: After 18 hours of potting, remove the tooling and trim the appearance of the product;

[0012] Step 8: Perform secondary wiring assembly work on the product;

[0013] Step 9: Conduct full performance tests on the product.

[0014] Preferably, in step 2, the thickness of the lower polyurethane resin layer is 5 - 10 mm.

[0015] Preferably, in step 3, the distance from the surface of the silicone rubber particle filling layer to the top of the housing is 25 - 30 mm.

[0016] Preferably, the housing is made of insulating material.

[0017] Preferably, the amine catalyst is N,N-benzyl dimethylamine.

[0018] The beneficial effects of the present invention are as follows: Based on the original material polyurethane resin, a specific catalyst is added to change the original viscosity performance of the material. The improved polyurethane resin is used to meet the error requirements of a certain type of transformer under special high and low temperatures, thereby improving the first-pass rate of the product in the first production, reducing costs and ensuring the construction period. Description of the Drawings

[0019] Figure 1 It is a schematic cross-sectional view after potting a certain type of zero-sequence product with polyurethane.

[0020] Figure 2 It is a schematic diagram of the potting process operation steps and descriptions.

[0021] Markings in the figure: 1 - upper polyurethane resin layer, 2 - silicone rubber particle filling layer, 3 - iron core, 4 - housing, 5 - lower polyurethane resin layer. Detailed Embodiments

[0022] To make the objectives, 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 some but not all of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0023] The specific implementation idea of the present invention is as follows: If we want the iron core inside the zero-sequence current transformer to be free from or less affected by the deformation of the iron core caused by the shrinkage during the curing process of polyurethane resin, there should be no polyurethane resin around the iron core; and the coil must be centered in the housing. In the existing technical solutions, direct potting with polyurethane resin is used. The method adopted in the present invention is to support the iron core with rubber particles around it and then cover it with polyurethane to achieve the effect as shown in the figure (see attachment Figure 1 ).

[0024] Under normal circumstances, polyurethane resin is formed by mixing resin component A and curing agent component B in a certain proportion, and its basic properties are shown in Table 1. Suppose when the rubber particle filling layer 2, iron core 3, housing 4, and lower polyurethane resin layer 5 in the attachment Figure 1 are all completed, if the polyurethane resin mixed normally is used for capping, the resin will penetrate down within ten seconds and come into contact with the iron core 3, and the desired effect cannot be achieved.

[0025] The correct approach: Add an amine catalyst (N,N-benzyl dimethylamine); that is, when mixing component A and component B, add a specific amine catalyst in proportion to increase the viscosity and have a certain fluidity at room temperature in a short time, and then pot it on the rubber particles to achieve the effect of being able to seal without penetrating downwards, so as to ensure that the iron core 3 inside is not affected or less affected by force, and ensure the production qualification rate of the product.

[0026] Operating steps and explanations (see attachment Figure 2 )

[0027] (1) Measure the resin component A and the curing agent component B respectively according to the ratio of 4:1 and the dosage.

[0028] (2) Stir and mix thoroughly and degas under vacuum.

[0029] (3) Use the above mixture to pot a layer at the bottom of the plastic shell made of insulating material, that is, the housing 4, with a thickness of about 5 - 10 mm to form the lower polyurethane resin layer 5, and cure it for later use; its function is to strengthen the strength of the bottom surface of the plastic shell; the insulating material of the housing can be: epoxy resin, unsaturated resin, polycarbonate, engineering plastic, phenolic plastic, rubber material, PC / ABS alloy, PC / PBT alloy, PC / PET alloy, PS / PS alloy, PC / PMMA alloy, PET, PVC. The plastic material here can choose ABS plastic which is a terpolymer of acrylonitrile (A)-butadiene (B)-styrene (S).

[0030] (4) Fill the bottom of the above-mentioned plastic case with silicone rubber particles. According to the size of the zero-sequence coil, make it located in the middle of the case cavity, then supplement and fill the rubber particles, level and compact them, so that the plane of the rubber particles is 25 - 30 mm away from the top of the case. The purpose is that the top of the case also needs to be potted with polyurethane resin, and the appearance should be ensured, and the rubber particles cannot be spread to the top. And use a tooling to fix the secondary outgoing terminal at the specified position;

[0031] (5) Mix the amine catalyst, specific name: N,N-benzyl dimethylamine, with the mixture of resin component A and curing agent component B at a ratio of 2 - 4 ml / Kg by weight, stir and mix thoroughly, degas under vacuum, and then let it stand for 15 - 25 min; its function is to give it a certain reaction time and increase its viscosity, but the lowest fluidity must be ensured (see Table 2);

[0032] (6) Pour the above-mentioned mixture onto a part of the plane of about 20 ml of rubber particles, observe whether the mixture still has permeability and can seep down, and observe whether there is a phenomenon of the mixture seeping down. If it seeps down, it means that the amount of accelerator is insufficient or the standing time after mixing is insufficient. If so, continue to stand for a period of time; if there is no seepage phenomenon, then the entire rubber particle surface can be potted to form the upper polyurethane resin layer 1, and control the potted surface to be 5 - 8 mm away from the top of the case; to ensure the appearance quality of the resin surface at the top of the case.

[0033] (7) When the potted surface hardens, use the mixture of resin component A and curing agent component B in a ratio of 4:1 to pot the remaining part and carry out defoaming treatment to ensure that the polyurethane resin surface is flat, bright, without bubbles, pits, etc.;

[0034] (8) After 18 hours of potting, remove the tooling and trim the appearance of the product;

[0035] (9) Carry out assembly work such as secondary wiring on the product;

[0036] (10) Conduct full-performance tests on the product. (The full-performance tests can generally include error, characteristics, secondary-to-earth insulation withstand voltage, insulation between secondary windings, secondary DC resistance tests, etc.).

[0037] On the basis of the original material (polyurethane resin), add a specific catalyst to change the original viscosity performance of the material (see Table 2); it can be seen from Table 1 that the viscosity of the polyamine mixture without adding a catalyst hardly changes within 40 min. If the viscosity at 25 min in Table 2 is to be achieved, it will take 80 - 90 min or even longer; it can be seen from Table 2 that the polyamine mixture with the added catalyst has almost no fluidity in viscosity at 25 min, reaching the performance requirements for use, and improving the production efficiency.

[0038] Use the improved polyurethane resin to meet the potting production requirements of a certain type of transformer with error requirements under special high and low temperatures (see Table 3). It can be seen from Table 3 that for the conventional polyurethane potting method (i.e., full polyurethane potting), although the error performance of the product is qualified at normal temperature and 70°C, at -25°C and -40°C, its ratio error is unqualified and the change at each point is irregular, unable to meet the product test performance requirements; while for the method of the present invention (i.e., adding rubber particles and polyurethane potting), the error performance of the product is qualified at normal temperature, -25°C, -40°C and 70°C, and the ratio performance is in good consistency with the semi-finished product debugging performance, which is convenient for production control and meets the customer's order requirements.

[0039] Table 1 shows the basic characteristics of a certain brand of polyurethane

[0040]

[0041] Table 2 shows the relationship between the viscosity of the polyurethane resin added with a catalyst and the standing time

[0042]

[0043] Table 3 shows the comparison of the error performance of the product after potting by the conventional method and this method at high and low temperatures

[0044]

[0045] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A potting method for polyurethane resin of a zero-sequence current transformer, characterized in that: It includes the following steps: Step 1: Thoroughly stir and mix the resin component A and the curing agent component B in a ratio of 4:1, and conduct vacuum degassing; Step 2: Use the above mixture to pot the bottom of the housing (4) to form a lower polyurethane resin layer (5), cure it for standby. The material of the housing (4) is ABS plastic; Step 3: Fill silicone rubber particles above the lower polyurethane resin layer (5). According to the size of the zero-sequence coil, make it located in the middle of the housing cavity, and then supplement and fill the silicone rubber particles, level and compact them; Step 4: Thoroughly stir and mix the amine catalyst N,N-benzyl dimethylamine with the mixture of the resin component A and the curing agent component B in a ratio of 2 - 4 ml / Kg, conduct vacuum degassing, and then let it stand for 15 - 25 minutes to ensure the lowest fluidity; Step 5: Pot the above mixture on the upper surface of the silicone rubber particle filling layer (2), observe whether there is any seepage of the mixture. If there is seepage, continue to let it stand for a period of time; If there is no seepage, the entire rubber particle surface can be potted, and the distance from the potted surface to the top of the housing (4) is controlled at 5 - 8 mm; Step 6: When the potted surface hardens, pot the remaining part with the mixture of the resin component A and the curing agent component B in a ratio of 4:1 and conduct defoaming treatment to ensure that the polyurethane resin surface is flat, bright, without bubbles and pits; Step 7: After 18 hours of potting, remove the tooling and trim the appearance of the product; Step 8: Conduct the secondary wiring assembly work on the product; Step 9: Conduct the full performance test on the product.

2. The potting method of the polyurethane resin of a zero-sequence current transformer according to claim 1, characterized in that: In the above Step 2, the thickness of the lower polyurethane resin layer (5) is 5 - 10 mm.

3. A potting method for polyurethane resin of a zero-sequence current transformer according to claim 1, characterized in that: In the above Step 5, the distance from the surface of the silicone rubber particle filling layer (2) to the top of the housing (4) is 25 - 30 mm.

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