The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is well understood that heavy rain can wash away contamination from the surface of high voltage (HV) insulators and thereby reduce the risk of pollution flashover. This study examines the cleaning effect of natural wetting conditions on HV insulators on four 500 kV transmission lines in Hunan Province, China. Historical meteorological data, monthly equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) measurements taken over a period of five years were analyzed to investigate the relationship between rainfall intensity and insulator cleaning. The measured data show that the ESDD/NSDD changes with the seasonal variation, which accumulates in dry season (January-April, about 117-122 days) and is washed off in the wet season (June-October, about 118-127 days). According to the measured data, the ESDD and NSDD on the surface of insulators were affected by the rainfall intensity (in the dry season it is about 1 mm/day and in the wet season it is about 5 mm/day). Based on a comparison of the four study sites, we propose a mathematical model to show the functional relationship between rainfall intensity and insulator self-cleaning capability. The mathematical model's coefficient of determination (R 2 ) is greater than 0.9 and the effective rate of self-cleaning capability reaches 80%.illogical combinations, such as agricultural and desert conditions, do occur in winter in some areas [4][5][6]. Due to the high accumulation rates of natural contamination from industry and agriculture on insulator surfaces in Southern China during the winter months, an insulator cleaning program has been devised for transmission lines in the region [7,8]. However, the cleaning scheme is always carried out in December and only once for every year, therefore it is not very effective and the insulator surface could not maintain cleanliness for the whole year. The accumulation of contamination will increase with the air pollution after a few months. Thereby, it endangers the safe operation of power networks.The accumulation of contamination is mainly divided into two processes: contamination of HV insulators is highest during the dry season and lowest during the wet season, when rainfall efficiently removes some of the surface contaminants [9,10]. At present, the research mainly focuses on the pollution accumulation process, studies on air quality index (AQI), size and gravity of particles, wind speed, electric field intensity, and the force of adhesion, etc. [11,12]. However, there have been few studies on the effect of rainfall flushing. The existing research relies on artificial rainfall experiment platforms [13][14][15][16]. However, artificial pollution tests on outdoor insulators mostly consider the parameters of ideal conditions and the test results are n...
