Application of shielded solid insulation for the complete switchgears at high voltage

The article describes the requirements for medium-voltage switchgears. It shows the main advantages and drawbacks of the conventional air-insulated switchgears and the relevance of the switchgears with solid insulation and solid shielded insulation. The use of this insulation system allows to reduce significantly the size of switchgear and to improve considerably the safety of its operation. The analysis of above mentioned characteristics of insulating systems with solid insulation in switchgear with solid shielded insulation (SISS) was carried out and there were given recommendations for the use of solid insulation. There were considered the main features of the SISS solid insulation: weakly inhomogeneous electric fields; high working electric field intensity; large volume of solid dielectric; high operating temperatures; usage of compact connections of adjoining insulation systems with solid insulation. There were defined typical insulation clearances of SISS: coaxial cylinders; special connectors; cable adapters; current leads and the insulating cases in the switchgears. The analysis of the known characteristics of the cast epoxy insulation and EPDM shows that the thickness of the insulation at high voltage in different standard insulation clearances, as a rule, may differ. It was determined that in order to ensure reliable operation of the SISS it is necessary to take special measures to exclude the possibility of gas spaces presence in the solid insulation.