Space charge inside oil paper insulation can severely distort the electric field distribution and lead to degradation of electrical performance of materials. A vast number of articles about the space charge characteristics of oil paper insulation under different conditions has been published; however

few report the influence of oil paper composition. In this paper

a comparison of the space charge distribution as well as the electrical conductivity of four combinations of transformer oil (Kunlun #25 and Nynas oil) and paper (type I from XD factory

type II imported from France) is carried out. The results show that the combination of type II paper and Kunlun oil performs well with minimal charge accumulation inside the materials. To understand the phenomenon

results of space charge measurements and electrical conductivity are associated. A microscopic inspection of two types of paper is conducted to acquire the surface condition of the paper. The relationship between space charge injection quantity and surface condition of the papers is discussed. It is observed that a relatively higher conductivity of oil as well as a smooth

dense surface of paper can suppress space charge in oil paper insulation.