| The necessary of energy-saving and loss reduction is explained with the help of the formula by analyzing transformer market competition and the rising factor of main raw materials. The manufacturing cost to the manufacturers and operating cost to the management can be saved due to the energy-saving and loss reduction. The traditional main insulation structure of 10kV, 35kV and 110kV voltage class transformers in domestic has been lagged because of the waste of manufacturing cost largely, so it is necessary to develop the new type of main insulation structure to meet the requirements of energy-saving and loss reduction. To confirm the running reliably and keep the advance of structure, the thesis starts from the basic principles, analyses the essence of kinds of breakdown, especially about the breakdown of oilpaper structure, and gives a detailed analysis using finite element method.The new design schemes of main insulation structure are presented to the power transformers of 10kV, 35kV, and 110kV voltage class respectively. Firstly, for the 10kV voltage class, the main insulation distance has been reduced from 9.5mm to 7.5mm. By analyzing and calculating the two kinds structures the rationality of new main insulation structure can be obtained. Secondly, for the 35kV voltage class, the electric field is concentrative overly if the main insulation distance has been reduced from 27mm to 18mm, so a special method must be adopted to guarantee the reliability. Comparing the manufacturing cost of the two examples, the advantage and practicability of the new main insulation structure is feasible. Thirdly, for the 110kV voltage class, the new main insulation structure is feasible according to the calculation and test report, even if the main insulation distance has been reduced from 40mm to 38mm.Based on above analysis and calculation, the conclusions are derived that the new insulation structure of 10kV, 35kV, and 110kV voltage class are advanced and meets the requirements of reliability.
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