Hollow pressurized and unpressurized ceramic and glass insulators for use in electrical equipment with rated voltages greater than 1000 V|Electric insulators, Electrical insulation devices, Ceramics, High-voltage equipment, Hollow, Switchgear, Electric control equipment, Rated voltage, Frequencies, Pressure, Bending stress, Loading, Type testing, Pressure testing, Bend testing, Thermal testing, Verification, Dimensional tolerances, Roughness (surface), Tolerances (measurement), Mathematical calculations