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Analysis of the performance of nonceramic insulators on 230 kV and 400 kV transmission lines

Nonceramic insulators have been applied in Mexico for about 15 years under various polluted conditions on 230 kV and 400 kV transmission lines. The operative condition of nonceramic insulators from 3 to 11 years in service is analyzed. The analysis is carried out by measurements of hydrophobicity, pollution level, visual corona, Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric (TGA). An ethylene propylene diene monomer rubber (EPDM) insulator of 31 mm/kV showed very light degradation on its surface after 9 years in service under non polluted conditions; although its hydrophobic property was low, signs of surface discharges were not observed. On polluted zones, silicone rubber (SiR) insulators are used. The most of the inspected insulators presented degradation on their housing. Severe damage was found on one insulator of 31 mm/kV which had been working for 2.4 years. The results show that the insulators with less damage and more time in service are those having a specific leakage distance of 39 mm/kV or a 52% of silicone rubber.