The space/interface charge problem in polymer dielectric has been the hot research field in domestic and abroad. Converter transformer is the most important equipment in HVDC transmission project. The accumulation of space/interface charges in oil-paper insulation system will directly lead to the distortion of local electric field distribution which can cause the breakdown

surface flashover

accelerated aging of insulating medium and so on

and is an important factor that impairs the safe and stable operation of converter transformers. We summarized and analyzed achievements in the research of space/interface charge of oil-paper insulating dielectrics in recent 20 years. First

we presented the latest progress in the space/interface charge measurement and simulation for oil-paper insulating composite dielectrics. Then

we discussed the influences of different voltage types（DC

AC

DC+AC

polarity reversal）

field strength

temperature gradient and oil-paper bulk state on the space/interface charge evolution

and analyzed the relationship between space/interface charge dynamic behavior and the insulation performance. Finally

we put forward the suppression methods for space/interface charge of oil-paper insulation. A great deal of valuable achievements in research on space/interface charge of oil-paper insulation canprovide a theoretical support for the design of insulation structure and the improvement of insulation performance of equipment. Moreover

it is needed to further research the measurement and simulation of space/interface charges of large-scale oil-paper insulation structures

the micro-correlation mechanism between space/interface charges and insulation properties of materials

and advanced electrical insulating materials with excellent insulation properties.