Insulation co-ordination of UHVDC transmission lines

The external insulation coordination is one of the key technologies in the UHVDC power transmission projects and deserves further studies. External insulation mainly contains two parts, the insulation coordination of insulator and coordination of air gaps in transmission. Some frequently-used types of insulators are selected and compared from their service life and electrical performance. Two widely used methods, leakage distance method and pollution withstand voltage method are used to calculate the number of insulators. Statistical method is adopted to coordinate the air gap of transmission line. The insulators´ selection in different areas has been calculated, and the air gap distance is coordinated. Research shows that, shed insulator has good pollution withstand property, could be used in light polluted area. Composite insulator has excellent antifilthy spark overability, it could be applied in medium or more serious polluted areas. In icing serious area, insulation performance of the composite insulators suffers great declination, porcelain insulator is recommended to be used here.