Abstract:
The present invention relates to an active part of a dry-type distribution transformer having an insulation system with electrical field control. An active part of the dry transformer comprising a core (1) with yokes (2) and limbs (3) having an a longitudinal axis (A) around which LV coils (4) and winding bobbin (5) is placed concentrically. The bobbin (5) has a shape of a longitudinal cylinder (5a) which is ended with annular discs (5b). The bobbin (5) is made of material having a dielectric permittivity which is two to five times higher more the dielectric permittivity of the insulating body (8) surrounding the limb (3) around the axis (A), in which the LV coils (4) and HV coils (6) are embedded. The external facial surfaces of the insulating body (8) is provided with a metallic layer (10) having such electric conductivity that the part of the insulating body (8) between an internal surface of the metallic layer (10) and an external surface of the annular disc (5b) has a thickness (d3) which is sufficient for insulation. A side surface of the cylinder (5a) is covered with a resistive layer (7) being a control shield of an electric field around the limb (3) of the core (1) and the HV coils (6) and the LV coils (4).