The Study On Oil-Flow Electrification Characteristics Of Oil-Paper Insulation In Converter Transformer

Converter transformer plays an important role in HVDC (high voltage direct current) transmission system, its reliability directly impact on the safe operation of power system.The operating converter transformer not only withstands AC voltage, lightning impulse and switching overvoltage, but also DC voltage, superimposed AC-DC voltage and polarity reversal voltage. Therefore, there are considerable differences in the characteristics of electric field between a converter transformer and a power transformer in inner electric field's distribution, breakdown characteristics of insulation material, space charge's accumulation and distribution, oil-flow electrification. All of these may cause abnormal discharge and breakdown in the converter transformer.This thesis mainly studies the il-flow electrification by experimentation. Firstly, In order to study oil-flow electrification characteristics and breakdown characteristics of converter transformer, the experimental model of oil-paper insulation is established, the oil-flow electrification and breakdown testing system is built after designing. Secondly, to study the oil-flow electrification characteristic of oil-paper insulation on different voltage, both the superimposed AC-DC testing system and electrode system are designed, and then a correlative preprocessing system and measuring system are established. At last, the oil-flow electrification characteristics of oil-paperboard at various oil velocities and different temperatures are studied under AC voltage, DC voltage and superimposed AC-DC voltage through test. The results show that streaming current becomes higher at the higher temperature and velocity of transformer oil, similarly, the streaming current is proportional to the value of AC voltage, DC voltage and superimposed AC-DC voltage. When the values of different voltages are equel, the streaming current under DC voltage is higher than under AC voltage.The study can be referred to the insulation design of converter transformer and the HVDC apparatus testing.