Study On Influence Of The Breakdown Characteristic Of Oil-paper Insulation In Converter Transformer Under Different Temperatures

The converter transformer has become to be one of the core apparatus for the HVDC (high voltage direct current) transmission system, and its reliability directly relates to the safe operation of the system. Compared with a normal transformer ,the operating converter transformer not only withstands AC voltage, lightning impulse and operative-over voltage but also DC voltage, superimposed AC-DC voltage and polarity reversal voltage. Under the different excited voltage, the electric field's distribution of insulation structure of the converter transformer and breakdown characteristics of insulation material are more complicated, so it is necessary to analyze the electric field's distribution and breakdown characteristics of oil-paper combination insulation.Firstly,in order to study electric field distribution in the oil- paper insulation under the different excited voltage forms, the simplified oil- paper insulation model is established. The electric field's distribution of the insulation under different excited voltages is simulated with FEM (Finite Element Method), and the theory is also demonstrated with the mathematical methods.The law of the electrical field distribution is summarized under different excited voltages, and the factors influencing the field distribution characteristics have also been studied.Secondly, to study the breakdown characteristic of oil-paper insulation, the thesis designs and builds a complete breakdown system and pre-test and detection devices of oil-paper insulation on consideration of combined with existing laboratory equipment.At last, the breakdown characteristic of paperboard, oil and oil-paperboard under AC voltage, DC voltage, superimposed AC-DC voltage and polarity reversal voltage with different temperatures is studied through test, The results show that many factors determine the breakdown characteristics of oil-paper insulation under different excited voltages and different temperatures .Although it is complex ,but it has certain laws.The research results can be referred to the insulation design of converter transformer and the HVDC apparatus testing.