1) the short circuit capacity, there is no doubt that epoxy pouring type is the best because of its winding is in overall within the mold casting, the heat curing, thus forming a high mechanical strength of the cylinder, thus has the very high amplitude in the structure with the axial mechanical strength, no matter from the run practice or sudden short circuit test results confirmed that.
2) the impact of overvoltage and insulation properties, also with epoxy pouring type is better because impregnated kind of dry type transformer coil, mainly USES the cake and bread as insulation medium air its insulation strength is greatly lower than that of epoxy resin, so relatively speaking, the size of the dipping type dry become larger, and the corresponding capacitance is small, so under the action of impact overvoltage of overvoltage and poor distribution characteristics. According to the experience of the United States, even the impregnated OVDT dry transformers using DuPont's Nomex paper and VPI process, the maximum benchmark impact level can only reach 150kV, and accordingly only 35kV dry transformers can be manufactured. On the contrary, the internationally recognized epoxy casting dry transformers can reach 250kV, that is, 66/77kV dry transformers can be manufactured.
3) From the perspective of heat dissipation, the epoxy casting dry transformer adopts layer windings, and multiple heat dissipation air ducts can be set along its axial direction, so large capacity dry transformer can be produced. On the contrary, as mentioned above, the impregnation dry transformer adopts pie coil, and its heat dissipation and ventilation is poor. According to the current international recognition, the maximum capacity of epoxy casting drying can reach 20MVA, while the impregnation drying can only reach 8-10MVA. Therefore, in order to manufacture high voltage, large capacity dry transformer, the current conditions are not epoxy casting type.
4) runtime overload capacity, specific analysis should be done to this, first of all, in theory, the overload capacity of the dry change is directly proportional to the heat capacity, and is inversely proportional to the load loss, then dip type dry become self cooling capacity is not superior to the epoxy pouring type do change, so, must not simply dipping type dry become the overload capacity must be superior to the epoxy pouring type dry. For the impregnated dry transformers, the overload capacity of the impregnated dry transformers is high only when NOMEX insulating paper is used not only for the turns but also for the insulating parts such as support bars and pads. This is due to the fact that Nomex paper is a Class C insulating material that can withstand the heat up to 220 ° C, so it is used to make a Grade H (180 ° C) dry change. There is an overload heat margin of about 20% from the beginning. However, due to the high price of Nomex paper, the current manufacturers of impregnated dry transformers in China often use Nomex paper only for turn insulation. Therefore, such a dipping dry transformation cannot be considered to have superior overload capacity to that of an epoxy casting transformation.
5) From the point of energy saving and consumption reduction, because the mainstream products of the current domestic impregnated dry transformer are H class, its loss standard will be significantly higher than that of the F class epoxy casting dry transformer. Therefore, the use of H-class impregnated dry transformer (namely the so-called OVDT dry transformer), is obviously adverse to energy saving.
6) Oxygenic resin dry transformer moisture resistance and corrosion resistance is particularly good, especially suitable for working under extreme harsh environmental conditions on the contrary, the main disadvantage of the traditional immersion dry transformer is poor moisture resistance, and easy to vacuum, need to preheat before being put into operation. Even with new processes such as Nomex paper and vacuum pressure immersion (VPI), these shortcomings have been overcome to a certain extent, but some fundamental problems remain. In particular, the quality of impregnation will affect the reliability and local release performance of such products to a large extent.
7) In terms of environmental protection, both epoxy resin and Nomex paper are organic materials, which cannot be naturally degraded. After the end of their operating life, there are problems such as degradation treatment, recycling and recycling. Many years of experience abroad has proved that the two types of dry transformers do not pollute the environment in the manufacturing process, and the factory recovery has been realized, and there is no problem in environmental protection. Especially in the recovery and treatment of epoxy casting dry transformation, there are already mature experiences in European countries.
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