The equivalent salt density measurement of pollutants on the surface of insulators shall be conducted for one year. Refer to Appendix B for the pollution level and corresponding salt density value to check whether the measured salt density value is consistent with the local pollution level. Based on operational experience, the measured values are used as a basis for adjusting the pollution resistant insulation level and supervising the safe operation of insulation. When the salt density value exceeds the specified value, measures such as climbing, cleaning, and coating should be taken according to the situation. Samples should be taken from at least one suspension insulator (or suspension test string) and one rod type post insulator representing the local pollution level every 5km to 30km of outdoor lines. The measurement should be conducted during the period of the heaviest pollution accumulation in the local area. Infrared temperature measurement should be conducted at the 500kV substation; Twice a year; 110kV and 220kV substations: once a year

② 110kV and above lines: sampled and inspected at least 5% annually according to DL/T664-1999 using infrared thermal imaging. Note: The test items for pin type post insulators and suspension insulators during operation can be selected from zero value inspection, insulation resistance inspection, and AC voltage withstand test. Glass insulators shall not undergo the tests in items 1, 2, and 3. Insulators that self explode (break) during operation