Abnormal heating of composite insulators is a hidden threat to safe operation of transmission lines. Although moisture is considered the key factor leading to temperature rise in high humidity areas

specific position and diffusion path of moisture are unclear for newly-installed composite insulators. In this paper

microstructure analysis and moisture absorption tests are first conducted to find the specific position of the moisture. Also

an accelerated water penetration test is used to demonstrate influence of moisture on the temperature rise. Former experiments find that moisture is concentrated at voids near the interface and surface of the Aluminum hydroxide (ATH) particles in housing material. For newly-installed composite insulators

moisture could spread to voids through failed fitting sealing and interface bonding

however

permeation through the housing is invalid. Later tests find that moisture at the surface of ATH could increase temperature at the high-voltage end and moisture in the void could lead to an additional heating area outside the high-voltage end. Temperature rise of additional heating area is dependent on length of the unbonded interface next to fitting. According to results of finite element simulation

the additional heating area is caused by increase of electric field strength at both ends of the moisture area. The additional heating area outside the high-voltage end could be used as a feature of sealing and the bonding defect of newly-installed composite insulators.