Overhead lines (OHL) operating at 400kV, form the backbone of CLP Power's transmission network. Unlike underground cables, overhead lines are vulnerable to external environmental attacks, such as adverse weather, high humidity, pollution, ground stability, vegetation, and flying objects etc. To ensure high reliability and availability of the overhead lines for bulk electricity transmission, cost effective maintenance strategies including the application of specific accessories and materials, such as lightning arrestor and high voltage insulation coating (HVIC) as well as tower refurbishment to mitigate the risks caused by lightning, pollution and typhoon are essential. CLP Power (CLPP) has adopted both preventive and condition-based strategies for Transmission overhead line (TOHL) maintenance for many years and has accumulated a lot of valuable experience and knowledge on the implementation of various maintenance and refurbishment practices. These practices have led to the achievement of world class service performance and contributed in the long term economic growth of Hong Kong. (6 pages)