Effect of Electric Field on Conductivity of Synthetic Ester Immersed Kraft Paper

Recent decades have witnessed rapid global application of the HVDC system in long distance electrical energy transmission or interconnection of different power networks. However, the failure rate of the HVDC system is higher than the conventional AC system. The high failure rate is mainly attributed to the malfunction of converter transformers under the AC plus DC working condition. Synthetic ester has emerged as an environmentally friendly alternative to traditional insulating liquids for their biodegradable/environmentally friendly nature and fire safety feature. Also, research indicated their potential of prolonging the lifetime of paper insulation. This paper assesses the applicability of ester in converter transformers from the perspective of conductivity, which is a crucial parameter for the design and maintenance of converter transformers. Experimental studies were designed to unravel the effect of electric field on the conductivity of the ester immersed Kraft paper. The test results indicated a positive correlation between short-term conductivity and the electric field, while long-term conductivity exhibited a non-linear trend.