Insulator Pollution Performance at High Altitude: Major Trends

A survey of the data available from the literature was conducted in order to assess major trends in insulator performance with altitude. The literature comprised tests on individual insulator strings both under natural and artificial conditions along with actual live-in performance. The major trends reported here suggest a pressure dependence (p/po)0.35 for DC and (p/po)0.5 for AC, of V50 for standard polluted insulators at altitudes lower than about 4 km (p ~ 0.6 atm). These pressure dependences impose a derating of the relative performance of leakage path length or flashover voltage with altitude, namely 6%/ km for AC, 5%/ km for positive DC and 4%/ km for negative DC applied voltages. Dielectric breakdown, in contrast, imposes a 10.5%/ km degradation of insulating air gaps with altitude.