Development and Investigation of Silicone Rubber Medium-Voltage Bushings with 3D-Printed Electrodes

Inhalt:
A new method to manufacture geometrically graded bushings for a voltage of Um = 24 kV was developed in which the field grading electrode was produced together with the flange of the bushing in one piece from a conductive resin using the Stereolithography (SLA) 3D-printing process. The grading electrode has a complex Borda structure that can be produced very easily using a 3D-printing process compared to other production methods. The grading electrode as well as the inner conductor, which was made from stainless steel, were cast in silicone rubber using a mold, that in turn was produced in an SLA process. An RTV 2 silicone with a Shore hardness of 45 ShA was used for the casting process, which was carried out under vacuum to prevent air bubbles in the silicone rubber. Five bushings were successfully produced with a diameter of the insulating body of 44 mm and a length of 129 mm. The bushings were tested for their partial discharge (PD) properties and reached PD extinction voltages between 47 kV and 68 kV for a PD level < 5 pC, which means they were all well above the limit of 20.8 kV for Um = 24 kV. This proves the good quality of the vacuum casting and the adhesion of the silicone rubber to the molded-in conductive parts. All bushings also passed the AC withstand voltage test at 50 kV for 5 min. One bushing was tested to the limit and reached a comparably high AC breakdown voltage of 85 kV.