Transformer Insulation Electrical Strength Research

During the development of electric power, power transformers are widely used in the distribution network of power plants, substations, industry, commerce, and domestic consumer. The reliability and the service life of the transformer is determined by its insulating properties. The main factors that influence the transformer insulating level include the protection, temperature, humidity, and overvoltage of the environment of the insulating parts, in which the overvoltage is most important one. Moreover, transformers need to endure high amplitude of lightning impulse overvoltage and switching impulse overvoltage. Some transformers may be subjected to very fast transient overvoltage-related overvoltage so that the insulation suffers significant voltage drop under abnormal operating condition, leading to the high centralization of the electric field and may cause the damage of the major and minor insulation of the transformer.Therefore, it is necessary to study the capacity of power transformer insulation to endure fast transient overvoltage, especially the wave processes. The main content of this study includes:1) the insulating properties of the conductor paper insulation of transformers,2) the theoretical calculation and simulation validation of the capacity of winding model to endure lightning overvoltage, operational overvoltage, Very fast transient overvoltage,3) the gradient voltage distribution under the lightning impulse voltage and switching impulse voltage,4) the voltage gradient when the very fast transient overvoltage, lightning overvoltage, and switching impulse overvoltage work on the insulating model with the same winding structure. By software simulation validation and experimental result comparison, we obtained the corresponding wave processes of winding with different structures and different arrangements, and found out the weakness of the winding insulation to be enhanced. By adjusting the transformer winding insulation, coil form and winding arrangement structure, the capacity of transformers to endure transient overvoltage and the stability properties of transformers can be improved, and the manufacturing cost of transformers can be reduced, which have great significance for the development of extra high voltage transformers.