Influence of Impurity Concentration on Insulation Strength of Insulating Oil under Different Voltage Types

Abstract

Converter transformer is the key equipment of high voltage direct current transmission system. The insulating performance of transformer oil is quite sensitive to nonmetallic and metallic particles originating from the process of installation and operation of converter transformers. As to the high electrical field, the particle easily leads to partial discharge and breakdown in transformer oil. This paper construct the AC/DC composite experiment platform. And the breakdown voltages of transformer oil with different carbon particle diameter or concentration level are investigated at AC, DC and combined AC and DC voltage, respectively. The influence of carbon particle diameter, concentration and voltage type on the breakdown strength of insulating oil are obtained. The experimental results showed that the breakdown voltage of insulating oil with carbon particle approximately comply with Waybill distribution. The voltage type has a significant influence on the breakdown voltage of insulating oil. The breakdown voltages are decrease under AC voltage, combined AC and DC voltage and DC voltage. With the diameter and concentration of carbon particle increase, the breakdown voltage of insulating oil will decrease. The analysis result shows that the carbon particle will form carbon particles bridges, and which will affect the breakdown voltage of insulating oil.