In-Situ Monitoring of Electrolytic Corrosion on the Caps of HVDC Insulators

The evaluation of the electrolytic corrosion on the hardware of insulators is necessary for long-term operation and maintenance of high-voltage direct current (HVDC) overhead lines. In this paper, the design and development of an online monitoring system are introduced for the measurement of corrosion current and the charge in porcelain and glass disc suspension insulators. A wide range current sensor of a
$\mu \text{A}$
-mA level was developed to sample the surface corrosion current. The data acquisition module connected to microampere current sensors, ambient temperature, and relative humidity sensors transmitted filed information to a remote Internet server via general packet radio service. Laboratory tests were carried out to verify the system performance, including the accuracy of current measurement, the stability of power supply, the reliability of communication, and electromagnetic compatibility. It was found that there was good agreement between the monitoring results and the dissection results. Six devices were installed on transmission towers of three ±800-kV HVDC projects in different regions, and all of them have been operating for more than two years from 2015 to 2017. Data stored in the server were exported for further analysis in this paper. Summary statistics on different time scales showed the relationship between corrosion and regions. Based on the records of the most seriously corroded caps, relative humidity and rainfall were found to be two major factors affecting the corrosion rate.