tailieunhanh - transformer engineering design and practice 1_phần 10

Đối với kiểm tra điện áp AC tần số điện, phân phối điện áp là tuyến tính đối với số lượng lần lượt và có thể được tính toán chính xác. Đối với việc tính toán sự phân bố điện áp xung trong các cuộn dây, họ được yêu cầu để được mô phỏng trong một mạch tương đương bao gồm gộp các yếu tố R, L và C | 8 Insulation Design Insulation design is one of the most important aspects of the transformer design. It is the heart of transformer design particularly in high voltage transformers. Sound design practices use of appropriate insulating materials controlled manufacturing processes and good house-keeping ensure quality and reliability of transformers. Comprehensive verification of insulation design is essential for enhancing reliability as well as for material cost optimization. With the steady increase in transmission system voltages the voltage ratings of power transformers have also increased making insulation content a significant portion of the transformer cost. Also insulation space influences the cost of active parts like core and copper as well as the quantity of oil in the transformer and hence has a great significance in the transformer design. Moreover it is also environmentally important that we optimize the transformer insulation which is primarily made out of wood products. In addition with the associated increase in MVA ratings the weight and size of large transformers approach or exceed transport limits. These reasons together with the everincreasing competition in the global market are responsible for continuous efforts to reduce insulation content in transformers. In other words margin between withstand levels and operating stress levels is reducing. This requires greater efforts from researchers and designers for accurate calculation of stress levels at various critical electrode configurations inside the transformer under different test voltage levels and different test connections. Advanced computational tools . FEM are being used for accurate calculation of stress levels. These stress levels are compared with withstand levels which are established based on experimental published data. For the best dielectric performance reduction in maximum electric stress in insulation is usually not enough the following factors affecting the withstand 327 .