1) Seen by the ability of short circuit, the epoxy casting type is the best because its winding is integrally cast in the mold and formed by heat curing to form a cylinder with high mechanical strength, thus having a structural High amplitude and axial mechanical strength, both from operational practice or sudden short circuit test results confirm this.
2) The characteristics of the impact overvoltage and the insulation characteristics are also better in the epoxy casting type. Because the impregnated dry type transformer mainly uses the cake type coil, the air as the insulating medium between the cakes has a lower insulation strength than the epoxy resin. Therefore, relatively speaking, the size of the immersion type dry change is large, and the corresponding cake-to-cake capacitance is small, so the over-voltage distribution characteristic under the impact overvoltage is poor. According to the experience of the United States, even with DuPont's NOMEX paper and VPI process impregnated OVDT type dry change, the benchmark impact level can only reach 150kV, which can only produce 35kV grade dry change. On the contrary, it is internationally recognized. Epoxy cast dry transformers up to 250kV can produce 66/77kV grade dry variations.
3) From the perspective of heat dissipation, the epoxy casting type dry change adopts layer winding, and a plurality of heat dissipation air channels can be disposed along the axial direction thereof, so that a large capacity dry change can be manufactured. On the contrary, as described above, the immersion type dry change Due to the use of the pie coil, the heat dissipation and ventilation conditions are poor. According to current international recognition, the maximum capacity of epoxy cast dry change can reach 20MVA, while the impregnation dry change can only reach 8-10MVA. Therefore, in order to manufacture high-voltage, large-capacity dry-change, under the current conditions, non-epoxy casting is the only one.
4) In terms of overload capability during operation, this should be analyzed in detail. First, theoretically, the overload capacity of dry change is proportional to its heat capacity and inversely proportional to its load loss, and then immersed dry change. The self-heat dissipation capability is not superior to the epoxy cast dry change, so it is absolutely impossible to simply say that the overload capacity of the immersion dry change is superior to the epoxy cast dry change. For immersion dry change, such immersion dry change has a strong overload only when the insulation of the wire truss is made of American DuPont NOMEX insulation paper, and insulation parts such as support bars and spacers are also used with NOMEX. ability. This is because NOMEX paper is a Class C insulation material, and its heat resistance temperature can reach 220 ° C, so it is used to produce a dry change of Class H (heat resistance temperature of 180 ° C). At the beginning, there was an overload thermal margin of about 20%. However, as far as the status quo is concerned, due to the high price of NOMEX paper, the manufacturers that produce impregnated dry-change in China are often only used for insulation. Therefore, such an impregnated dry change cannot be considered to have an overload capacity superior to that of an epoxy cast type.
5) In terms of energy saving and consumption reduction, since the mainstream products of domestic impregnated dry-type transformers are all H-class, the loss standard will be significantly higher than that of F-class epoxy casting dry-type. Therefore, the use of a Class H impregnation type dry change (so-called OVDT dry change) is clearly disadvantageous for energy saving.
6) Oxygen resin type dry change is particularly good in moisture resistance and corrosion resistance, especially suitable for working under extremely harsh environmental conditions. The main disadvantage of the traditional immersion type dry change is that it has poor moisture resistance and is easy to vacuum and is put into operation. Preheating is required before. Even though new technologies such as NOMEX paper and vacuum pressure immersion paint (VPI) are used today, although these shortcomings have been overcome to some extent, some essential problems still exist. In particular, the quality of the impregnation will largely influence the reliability and PD performance of such products.
7) In terms of environmental protection, no matter whether the epoxy resin or NOMEX paper is an organic material, it is impossible to degrade naturally. After the end of its operational life, there are problems such as degradation treatment, recycling and recycling. Years of experience abroad have proved that these two types of dry-type transformers do not pollute the environment during the manufacturing process, and have achieved factory recycling, and there is no problem in environmental protection. Especially in the recycling and treatment of epoxy cast dry change, there are already mature experiences in European countries.
