Oil transformers in hermetically sealed completely filled with transformer oil and do not have the expander, and the temperature changes its volume by heating and cooling are compensated volume change ripple tank walls. These transformers are filled with oil under vacuum, thereby increasing the electric strength of insulation. Dry transformer, as well as oil, consists of a magnetic circuit, windings HV and LV, enclosed in a protective casing. The main insulating and cooling medium is air. However, the air is less than perfect insulating and cooling medium than the transformer oil. Therefore, in dry transformers are isolation gaps and vents do more than oil. Dry transformers are manufactured with the windings stekloizolyatsiey with heat resistance class B (TAP), as well as insulated silicone varnish class H (TSZK). To reduce the hygroscopicity of the winding is impregnated with a special varnish.
Use as insulation winding fiberglass or asbestos can significantly increase the operating temperature of the windings and a virtually fireproof installation. This feature allows you to dry-type transformers used for their mounted inside the dry areas in cases where fire safety ustanovkiyavlyaetsya deciding factor. Sometimes the dry-type transformers replace more expensive and difficult to manufacture sovtolovymi. Dry transformers have several large dimensions and weight (TAP) and a lower overload capacity than oil, and used to work in confined spaces with a relative humidity of not more than 80%. Benefits dry-type transformers carry their fire (no oil), the relative simplicity of design and relatively low operating costs. The classification of current transformers current transformers classified by various characteristics: 1.