Naito - NCK ۱nsu۱ators. Ltd . Mizuho .Nagoya. Japan
Matsui - NCK ۱nsu۱ators. Ltd . Mizuho .Nagoya. Japan
Suzuki - NCK ۱nsu۱ators. Ltd . Mizuho .Nagoya. Japan

The insulator string design in a heavy pollution area is determined by insulator pollution performance. The insulator performance contains pollutant accumulation characteristics, withstand voltage characteristics of the polluted insulators, etc. Test results on various kinds of insulators in the field and at laboratories are studied and based on these test results anti-pollution design of the insulator string is explained. Corrosion of insulator hardware (cap and pin) is another problem in a pollution area. Based on investigation results, countermeasures against such corrosion are found, i.e. zinc sleeve for protection of the pin and zincaluminum coating for protection of the cap. In a mountainous area, the insulator string design is sometimes determined by the withstand voltage characteristics of the insulators covered with snow or ice. Based on the test results in the field and at the laboratory, the performance of the insulators covered with snow or ice is explained.