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| Study on Transient Insulation Condition of Converter Transformer Based on Nonlinearity Between Temperature and Electric Field |
| Yang Fan1, Chi Cheng1, Liu Gang2, Cheng Li1, Ou Shucheng3 |
1. State Key Laboratory of Power Transmission Equipment & System Security and New Technology Chongqing University Chongqing 400044 China;
2. Hebei Provincial Key Laboratory of Power Transmission Equipment Security Defense North China Electric Power University Baoding 071003 China;
3. Baotou Power Supply Bureau of Inner Mongolia Electric Power Group Co. Ltd Baotou 014000 China |
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Abstract Converter transformer bears high voltage during operation, and the internal insulation system has high temperature, large electric field intensity and obvious coupling phenomenon. However, the traditional insulation design method does not consider the nonlinear insulation characteristics.. First, a three-electrode experimental platform is constructed to analyze the coupling phenomenon of insulating oil and oil-immersed paperboard at different temperatures and electric field intensities. Results indicate that the electrical conductivity of insulating materials is greatly affected by temperature and electric field intensity, in which the inflection point of insulating oil is 2kV/mm, and the electrical conductivity presents a U-shaped nonlinear curve that first decreases and then increases. Then, a practical converter transformer model is built with refine insulation layer, collar ring and spacer to calculate transient insulation condition with the effect of temperature and electric field. It indicates that converter transformer has larger temperature range and the maximum temperature growth can be up to 68.7K, meanwhile the concentrated temperature area is next to the larger electric field region, so a strong coupling phenomenon cannot be ignored. Under polarity reversal condition, the maximum value of pressboard electric field with U-type electric-dependence increases 1.7kV/mm compared with exponential variation, and reaction rate would decrease in taking nonlinearity between temperature and electric field into account.
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Received: 25 November 2019
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2020, Vol. 35 
