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Application of epoxy resins for insulation in high-voltage electrical applicances
The application of insulating material has a long-standing history. In the early 20th century, European countries began to study this material. At that time, high-voltage stator coil was mainly used as raw material. Then the United States and other countries also began to study, which made insulating material emerge in endlessly. However, China did not begin to study this technology until the 1960s and 1970s, using acidic polyester to synthesize insulating material. The application of these insulating materials can be said to be the first shot in the history of material development in our country. Since then, China has continued to develop many insulation technologies. Epoxy resin is an insulating technology based on the background of this era. Its application is of great significance to the development of the entire power industry.
With the rapid development of social economy and the increasing number of high-voltage electrical appliances, the insulation of high-voltage electrical appliances has attracted more and more attention. Epoxy resin is the most common in current high-voltage electrical insulation systems. Its application is of great significance to the safety of the entire power system. With the continuous increase of voltage, the requirements for electrical insulation systems have become more and more stringent. The development of large-capacity power generation technology has promoted the increase of power voltage. It has also continuously made progress and optimization of insulation materials.
With the development of science and technology as well as the increasing progress of chemical industry, epoxy resin is becoming more and more complex. Its composition and combination methods are becoming more and more complicated. According to their composition we can divide epoxy resins into glycidyl esters, glycidyl ethers and aliphatic epoxy compounds. According to the current working status and working methods, we can divide epoxy resins into liquid epoxy resins and solid epoxy resins.
Due to its many unique advantages, such as high insulation performance, high structural strength and good sealing performance, epoxy resin has been widely used in the insulation and packaging of high and low voltage electrical appliances, motors and electronic components. It is mainly used for casting of electrical equipment and motor insulation packaging, including the manufacturing of integrally sealed insulating packages for high and low voltage electrical appliances such as electromagnets, contactor coils, mutual inductors and dry-type transformers. It has developed rapidly in the electrical industry from normal pressure casting and vacuum casting to automatic pressure gel forming.
Nantong Synasia New Material Co., Ltd. can provide three different types of cycloaliphatic glycidyl ester epoxy resins, including S-182, S-184 and S-186. In this post, we will introduce the specific application analysis of S-182 and S-184 in outdoor high-voltage electrical insulation. Due to excellent mechanical, thermal and dielectric properties, Synasia epoxy resins are widely used for insulation in outdoor electrical equipment.
01. 新納希產品介紹/Synasia product introduction
CAS no. 21544-03-6
Chemical name: tetrahydrophthalic acid diglycidyl ester
As a low-viscosity base resin, S-182 is best known for its excellent resistance to low temperature. This product can be cured with either amines or anhydrides. Itis suitable for insulating materials in casting bodies.
The appearance of epoxy cast insulators will not only improve the dielectric properties and mechanical strength of high-voltage electrical appliances, but also reduce the volume and quality of electronic devices. In the production of epoxy cast insulators, it is not only necessary to ensure its manufacturability, such as fluidity, casting temperature, gelation speed, curing speed, etc., but also to ensure that the glue has good cracking and high resistance during the curing process. This requires that in the production process, the heat of chemical reaction and its volume shrinkage should be small. Its thermal expansion coefficient should be close to that of the embedded solid part and the cured product should have higher mechanical strength.
CAS no. 5493-45-8
Chemical name: hexahydrophthalic acid diglycidyl ester
S-184 is low-viscosity difunctional cycloaliphatic glycidyl ester epoxy resin based on hexahydrophthallic anhydride. It can be cured with either amines or anhydrides. Because it is fully aliphatic, this product is well suited to withstand sun and uv exposure in outdoor use. When cured with accelerated anhydride curing agents, glass transition temperature in excess of 110℃ can be attained.
S-184 is used mostly in applications for outdoor electrical insulation designed for medium and high voltage. Because it is bisphenol-A free epoxy resin, this product is excellent for non-yellowing coatings, electrical insulating components, especially the insulating materials in casting bodies, e.g., transformer fillers.
Based on the application analysis of today’s epoxy resin, epoxy resin not only has the characteristics of good adhesion, scientific curing process, good heat resistance and high durability, but it also provides excellent resistance to corrosion and mechanical strength. It can meet various high-voltage wiring requirements in construction.
Most high-voltage electrical appliances usually operate in the open air. Therefore, the research and development of weather-resistant epoxy insulating paint is imperative. S-184 is especially suitable for the application of outdoor high-voltage electrical insulation materials due to its excellent weatherability.
With the construction of China's smart grid system and the continuously increased safety and reliability requirements of power transmission and transformation, outdoor high-voltage electrical products such as switches, insulators, transformers, mutual inductors and so on, which are important equipment for transmission and distribution. Oil-free and porcelain-free insulation has become an urgent issue in the power sector. At present, outdoor epoxy resin castables especially cycloaliphatic epoxy resins have gradually replaced silicone rubber. They have taken a leading role in the insulation of voltage levels of 10 to 110 kV.
02. 環氧樹脂澆注工藝/Epoxy resin casting technology
環氧樹脂澆注的工藝方法，從不同的工藝條件去理解有不同的區分方法。從物料進入模具的方式來區分可分為澆注和壓注；澆注指物料自流進入模具。它又分常壓澆注和真空澆注；壓注指物料在外界壓力下進入模具，并且為了強制補縮 , 在物料固化過程中，仍保持著一定的外壓，它由過去的簡單加壓凝膠法發展成現在成熟的自動壓力凝膠法。從物料固化溫度來區分，可分為常溫澆注法和高溫澆注法。
Epoxy resin casting method varies with different technical conditions. According to the way the material enters the mold, it can be divided into casting and injection molding. Casting refers to the self-flowing of the material into the mold. It is divided into normal pressure casting and vacuum casting. Injection molding means that the material enters the mold under external pressure, and in order to force the feeding, the material still maintains a certain external pressure during the curing process. It has developed from the simple pressure gel method in the past to the mature automatic pressure gel method. According to the solidification temperature of the material, it can be divided into normal temperature casting method and high temperature casting method.
According to the curing speed of the material, it can be divided into ordinary curing method and fast curing method. In modern casting technology, mature casting methods mainly include vacuum casting method and automatic pressure gel method. Epoxy resin casting is the process of casting epoxy resin, curing agent and other materials into a set mold, and then cross-linking and curing by a thermoplastic fluid into a thermoset product. At present, commonly used methods include vacuum casting method, normal pressure casting method and innovative epoxy resin full sealing technology.
03. 環氧樹脂發展趨勢/Epoxy resin development trend
The development direction of epoxy resin based electrical encapsulation and insulation materials is mainly to improve the heat resistance, dielectricity and flame retardancy of materials, and reduce water absorption, shrinkage rate and internal stress. The main ways of improvement include: synthesis of new epoxy resins and curing agents, higher purity of raw materials, modification of epoxy resins, such as toughening, softening, filling, strengthening, blending, etc., development of bromine-free flame retardant systems as well as the improvement of molding methods, equipment and technology. With the rapid development of semiconductor technology, the requirements for packaging materials are getting higher and higher. Ordinary epoxy resins can no longer fully meet the technical requirements.
For the improvement of epoxy resin technology, overseas companies mainly focus on:
Development of low-viscosity or low-melt-viscosity difunctional epoxy resins at present. With the use of high-content inorganic fillers, the internal stress of the packaged devices is greatly reduced, which helps minimize undesirable defects such as passivation cracking, loose wire, wire break, etc.
Development of multifunctional epoxy resins and at the same time introduce heat-resistant and moisture-resistant structural compounds into the epoxy resin, so that the packaged device can offer high heat resistance, low water absorption and low internal stress.
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