In order to explore the impact of the operation period and the shed structure to the contamination characteristics on AC composite insulator

this paper selects 24 composite insulators in high-cold area and investigates the natural contamination characteristics of insulators

specified in the ESDD and NSDD test method

including every parts of insulators.The results show that the composite insulator in Heilongjiang area have been in saturated stated after three years operation. Contrasting the results of different shed structure of insulators

it is found that the pollution of the one large two small structure is the lightest

the second one is one large one small structure

and the most serious is the porcelain post insulator. Through the analysis of the results

it is found that the upper surface is less serious than lower surface on the insulator itself;the pollution of insulator trunk is most serious

the second one is the small shed

and the large shed is the lightest.