Electrolytic Corrosion Charge Monitoring on the Hardware of Porcelain and Glass Insulators on HVDC Overhead Lines

Electrolytic corrosion of hardware is always a problem in porcelain and glass insulators on HVDC (high-voltage direct current) transmission lines. Leakage current and accumulative charges are for characterizing the corrosion rate and degree. In this paper, an approach for current measurement was introduced. Then, an equipment of high-precision and wide-range for corrosion current measurement was developed. The electrolytic corrosion test of insulators was carried out by salt spray method, and the corrosion current and charge were obtained. The data were compared and analyzed statistically. The results showed that the corrosion charges were different among insulators. The difference is irrelevant to the mode of insulator suspension. In addition, an on-line monitoring system for corrosion status was developed and installed on a ±500 kV HVDC transmission line. The corrosion current, charge of the target insulator string, ambient temperature and relative humidity were obtained. Data analysis showed that with the increase of relative humidity, the average value of corrosion charge and current changed in two trends, one was obviously increasing, and the other is decreasing slightly first and then increasing.