What Are the Defects and Causes of Porcelain and Dlass Disc Insulators for Overhead Lines?

1. The critical issue with ceramic insulator string failures lies in the occurrence of zero-value defects. The causes of low or zero values in ceramic insulators include poor quality, multiple lightning overvoltage impacts, and excessive external mechanical stress.

2. Targeted measures to address the low zero-value problem in ceramic insulators include enhancing zero-value detection, implementing diversionary lightning protection measures, and improving the line's lightning resistance level.

3. The spontaneous breakage of glass insulators results from the disruption of the balance between compressive and tensile stresses in the glass component. Common causes of a high spontaneous breakage rate include residual impurity particles within the insulator and excessive external contamination.

4. Spontaneous breakage caused by internal impurity particles is more likely to occur within the first three years of operation and gradually decreases thereafter. The probability of breakage is the same across different positions within the insulator string. If the fragments from the remaining cap are radial, the breakage is likely caused by internal impurities. For breakage caused by severe contamination, the probability is higher at the high-voltage and low-voltage ends of the string compared to the middle, and there is a correlation between breakage occurrences and variations in pollution sources.

5. In extreme cases, spontaneous breakage of glass insulators can also lead to string failures. In regions with high lightning activity, spontaneously broken insulators should be replaced promptly.

6. Corrosion of steel pins and steel caps in DC insulators results from anode corrosion due to electrolytic corrosion, with the wet layer on the surface of the shed plate acting as the electrolyte. Corrosion of the steel cap is concentrated around the edge of the cap, while corrosion of the steel pin is focused where it contacts the cement. Rusting of steel pins and steel caps in AC insulators is generally caused by oxidation after prolonged operation.

7. DC insulator steel pins should be equipped with zinc sleeves, and steel caps should have zinc rings. If the steel pins of AC insulators become corroded, they should be replaced as soon as possible.