Epoxy Resin Encapsulated Transformer Winding Casting Technology

1 Epoxy Resin Encapsulated Transformer Overview

Epoxy resin encapsulated transformers have been widely used in high-rise buildings and power stations in cities due to their characteristics of flame retardant, safety, reliable operation, convenient maintenance, and small size. In recent years, the production of dry-type transformers in my country has developed greatly. The number of manufacturers has rapidly increased from seven or eight in the early 1990s to nearly one hundred, and the production capacity has also increased from 3000~4000MVA to more than 20000MVA. The performance and appearance of the product have been greatly improved.

Most of the windings of epoxy resin encapsulated transformers are molded by epoxy resin casting (the low-voltage windings of many manufacturers are wound by copper foil), and the intrinsic performance of the winding after molding is also determined. If it fails to meet the specified standards, it has to be scrapped. Therefore, in order to ensure the pouring quality of the winding, the structure of the precast winding must be reliable. At the same time, it is required that the casting material formula of the winding should be reasonable, and the casting process should be advanced.

2 Epoxy resin casting process characteristics

The epoxy resin casting process belongs to the injection molding technology. It is a relatively mature process for casting windings in epoxy resin encapsulated transformers. It has been widely used in many countries in the world. Its main features are:

(1) The winding is fixed in the metal mold, and the injected epoxy resin mixture penetrates into the layers of the winding, and it is cured and formed, so that it is firmly combined with the wire and the insulating material. The cured and formed winding has a very High mechanical strength.

(2) Since both the winding and the resin mixture are degassed in a high vacuum state, after curing and molding, the partial discharge of the winding (measured results are generally below 10pC) is very low.