| Converter transformer plays an important role in HVDC (high voltage direct current) transmission system, its reliability direct affect to the safe operation of the system. The operating converter transformer not only withstands AC voltage, lightning impulse and operate-over voltage but also DC voltage, superimposed AC-DC voltage and polarity reversal voltage. Under the influence of these voltage, 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 of the converter transformer.This article mainly designed the oil-flow electrification and breakdown testing system. 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. According to the working condition of converter transformer, a circuit has been designed and simulated, which is made for the superimposed AC-DC test equipment, and then, a set of entire test equipment has been built by using the laboratory instrument. Moreover, the thesis detected in the Oil-Paper combination insulation of the space-charge, and put out the accumulation factors and the regulations of its changes. Finaly, the microcurrent detecting equipment is designed and made to measure the streaming current.The work in this paper provided a platform for investigating the factors and the characteristics of oil-flow electrification, the characteristics of breakdown and their interaction of oil-paper insulation in converter transformer.
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