The current state and possibilities for development of switchgears for a voltage of 6–35 kV

Abstract

General trends in the development of electrical-distribution systems and requirements for switchgears (SGs) for midrange voltage are considered. The main advantages of conventional SGs with air insulation are indicated. Problems of transitioning to SGs with solid insulation and solid shielded insulation are considered. The volume of cells with air insulation is from three to five times greater than that of present-day SG cells with solid insulation and gas-filled cells. It is determined that application of SISS (Solid Insulated Switchgear with an grounded Shield) technology shows the greatest promise for improving SGs with solid insulation. The solid shielded insulation extends the equipment’s service life before possible repair, thus decreasing the maintenance expenses. Various manufacturers’ schematic structural variations of manufacturing of cells with solid insulation are described. The main engineering solutions of the offered designs are presented. Their advantages and disadvantageous features have been indicated. Application of the proposed system allows one to reduce the size of SGs and significantly increase security, as contacts with high-voltage are not used in a compartment SG. In addition, the moving elements of SGs under high potential require another insulation medium that will allow these elements to move, e.g., a gas, liquid, or vacuum. This means that insulation of such SG in principle is combined. Moreover, the solid insulation layer worsens heat dissipation. High electrostatic-field strengths in solid dielectric and large volumes of molded solid dielectric require special means to eliminate partial discharges. Interconnection of various elements presents a serious problem, and the elements’ boundary surface is the most weakened insulation node. For this reason, application of such elements requires elaborate engineering and special engineering solutions that improve insulation’s performance reliability and improve thermal conditions.