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The porcelain insulators  resistance measurement
1)Porcelain Insulation resistance measurement is a measurement of the insulation resistance of the porcelain insulator, toughened glass insulators, composite insulators. The purpose of measurement is to check the condition of the insulation of the insulator, the insulator insulation deterioration and insulation breakdown and other defects.
(2) 35 to 220kV overhead power transmission line insulator insulation resistance measurement is recommended 5000V megger measurements.
A qualified insulation resistance standards
(1) newly installed insulators insulation resistance should be greater than or equal to 500MΩ.
Insulator (2) run the insulation resistance should be greater than or equal to 300MΩ.
2. Insulator deterioration determination principle
(1) insulator insulation resistance less than 300MΩ, and greater than 240mOhm can be determined to be low insulator.
(2) insulator insulation resistance is less than 240MΩ to determine zero value insulator.
The composite insulation generally do not use this method to test the insulation resistance.
3. Reasons lead to the deterioration of the disk-type suspension insulators
(1) the influence of temperature, the temperature influence on the insulation resistance is large, the insulation resistance decreases with a temperature rise. The reason is that the temperature increases, the polarization of the insulating medium exacerbated, conductance increases so that the insulation resistance decreases, change causes and the degree of temperature change and the insulating nature of the material, structure, and so on.
(2) the impact of humidity, humidity surface leakage current due to adsorbed moisture, insulating surface water film is formed, will make the insulation resistance is decreased.
(3) the deterioration of the insulator mechanical overload caused.
(4) porcelain pieces hygroscopic deterioration.
(5) pieces of porcelain, the deterioration of the internal and external stress overlap.
(6) causing the deterioration of porcelain insulators of thermal expansion.
(7) The steel cap poured mounted cement saturation expandable deterioration.
(8) The steel cap poured mounted cement to freeze expansion deteriorated.
(9) steel cap, steel foot electrical corrosion deterioration.
(10) the insulator over voltage caused deteriorated.
(11) the porcelain insulator internal defects caused deteriorated.