Design And Optimization Of Insulation Structure For Converter Transformer Bushing And Barrier System

Bushing and barrier system are key components in converter transformer; however, the insulation structure design and optimization of converter transformer bushing and barrier system always face technical difficulties. Considering sustained voltage types and actual demand, the simulation model is built combing with key bushing measurements, and barrier system electric field distributions are analysed under different voltage condtions, and the barrier system insulation structure is optimized. The research results are meaningful for improving converter transformer manufacturing level and realizing converter transformer bushing and barrier system localization.Firstly, three methods including equal capacitance, equal thickness and equal margin are used for designing condenser core in bushing inner insulation, and the software for calculating bushing inner insulation key measurements is written. The best bushing measurement is defined by comparing the main parameters calculation results under three methods, which provides reference for establishing simulation model.Secondly, the simulated model based on bushing measurement and barrier system structure is established. Then electric field distributions under AC voltage, DC voltage and polarity reversal voltage are calculated by FEM electric emulation software. The research results show that transformer oil with lower relative dielectric constant undertake higher field strength under the AC voltage, and insulating cardboard with higher resistivity have to bear higher field strength under the DC voltage, and the maximum field strength occurs in the insulating coating on the tulip surface. Moreover, the transformer oil will undertake extremely high field strength due to the space charge accumulation under the polarity reversal voltage.Then, the impact of operating temperature and water ratio for barrier system electric field distribution laws under DC voltage are analyzed. The research results indicate that temperature have obvious influence on barrier system electric field distribution under DC voltage. With reduction of temperature the electric field distribution in oil and cardboard are increasingly uneven. Additionally, with the growth of oil-paper insulation water ratio, the cardboard resistivity declines dramatically, and the oil resistivity just decreases slightly, and the maximum field strength of oil-paper insulation decrease with increasing water ratio.Finally, the insulation structure of barrier system is optimized, the influence of tulip arc radius to the maximum field strength is researched, and the fesibility of applying nonlinear insulating cardboard to replace tradition cardboard is discussed. The research results demonstrate that the maximum field strength could be decreased by increasing the tulip arc radius peoperly and the optimum size of arc radius is defined, and nonlinear cardboard could improve electric field distribution effectively.The study can be referred to the insulation design of converter transformer bushing and barrier sytem.