Insights from salt-fog testing on high-voltage insulators used in HVDC converter stations

The paper presents a dataset of insulators tested over recent years, covering porcelain, polymeric, and RTV-coated technologies and a wide range of site-equivalent salinity values.

Outdoor units were tested according to Italy’s contamination map, valve-hall insulators at 7 kg/m3, and DC-hall insulators at 14 kg/m3. Forty insulator types were evaluated, with differences in creepage distance, equivalent diameter, material, and voltage rating. Leakage current measurements collected during the tests provided additional diagnostic information, although no absolute threshold could be defined due to the strong influence of geometry and environmental factors.

The results show a correlation between meeting Terna’s creepage and site-equivalent salinity requirements and passing the salt-fog test. Based on the experience gained, insulators that have not passed the test following the procedure reported hereinafter, have experienced problems in the field. Although salt-fog testing does not predict long-term ageing, it remains an essential tool for verifying insulation behaviour under severe pollution and for reducing the risk of flashover in real operation. The findings confirm the validity of the proposed procedure included today in the IEC TS 63414.