Study On Dynamic Process Of Electric Field In Oil-Paper Insulation Structure At Reversal Polarity Voltage

HVDC (High Voltage Direct Current) transmission is a key means to realize the long-distance and high-capacity transmission, cross-sea power transmission. In recent years, HVDC transmission technology has got rapid developments. Converter transformer, as one of the most important equipment, is critical to the safe and reliable operation of the HVDC transmission system. But the running environment of converter transformers is complex. It is easy to lead to insulation problems. In many cases affecting the normal operation of converter transformer, oil paper insulation structure damage is the main factor caused the forced outage of converter transformer.For the above problems, this thesis is focus on the insulation problems, study the electric field and space charge distribution in the oil of oil paper insulation structure taking advantage of Kerr electro-optic effect based on the AC electric field modulation. The main content is as follow:(1) Research on the electric field and the space charge distribution characteristics of oil paper insulation structure under DC voltage.Based on the model of oil gap and single layer board covered electrode, measure the electric field distribution in oil under DC voltage, and set up the simulation model using the ion drift and diffusion theory. Experiment and the simulation results show that large amounts of space charge exist in the oil gap. And the distribution of space charge is not uniform. The space charge distribution is closely related to the applied electric field. Simulation results show that there is negative charge injection on the negative plate. Electric field is different under the positive and negative voltage in oil of the single layer board covered electrode model.(2) Research on the electric field and the space charge distribution characteristics of oil paper insulation structure under polarity reversal voltage.Based on the model of oil gap and single layer board covered electrode, measure the electric field distribution in oil under polarity reversal voltage, and set up the simulation model using the ion drift and diffusion theory. Based on the theory, analyzed the drift and diffusion of space charge in oil, charge injection on the interface of oil-mental and oil-paper. Experiment and the simulation results show that there is an obvious oscillation process of electric field in oil gap model under polarity reversal voltage, proving the ion changed the drift direction when the voltage polarity inversed. In the single layer board covered electrode model, there is a difference of charge drift and accumulation in paper, under different polarity. The electric field distribution is obviously asymmetry in the two different polarity reversal processes.