Analysis of Electric Field Data of Dry Type Transformer

Load and solve the core, iron yoke, clamps and low voltage winding set to zero potential, high voltage windings set to test frequency 35kV. The second type of homogeneous boundary is automatically satisfied. The calculation method is automatically selected by the ANSYS software for the user based on the physical properties of the problem. Here, the default wavefront solver is used to solve the problem and the calculation result is obtained. Post-processing If necessary, apply the PLNSOL, PLVECT, and GET instructions in the post-processing function to get corresponding graphs and data in the selected corresponding area for use during analysis. Calculation Results and Analysis Through the above calculations, the electric field strength values ​​in the dry power transformers under the action of a 35kV power frequency voltage can be obtained. From the calculation results, it can be seen that the calculated maximum electric field strength value is 2.0669106 V/m, which occurs at the intersection of the high-voltage winding and the insulating member (ie, z=0.205m) and also intersects the comb stay. This is consistent with the theoretical analysis of the partial discharge that is most likely to occur at the surface of the medium in contact with the solid medium. The surface where the maximum value of the entire model is located is the vector of the electric field in the z=0.205m plane.

Transformer solid insulators are prone to slip discharge, which can reduce and damage the insulation properties of solid insulation. Each insulator is specifically analyzed below. The yoke insulation yoke insulation is a solid insulation block between the clip and the winding that acts as a fixed and insulating member. Is a yoke-insulated electric field strength vector vector seen from the x direction. In the figure, the upper part is connected with the clamp part, and the lower part is connected with the winding. It can be seen from the figure that the maximum field strength in the yoke insulation appears at the junction with the top of the winding, and the minimum field strength appears at the junction with the clamp part. The calculated maximum field strength at the end of the low-voltage winding is 0.3139106 V/m; the minimum field strength is 41282 V/m; the ratio between the maximum and minimum field strength is about 7 times.

Comb stays Comb stays are insulating blocks used to wind high voltage windings. They act as a vector yoke insulated high voltage winding and insulation. It is a vector diagram of the electric field strength seen from a direction where both the x and z coordinates are 45. In the drawing, the leftmost surface is the surface that contacts the high voltage winding, and the rightmost surface is the surface that is in contact with the yoke. It can be seen from the figure that the maximum field strength appears on the face that is in contact with the high voltage winding; the minimum field strength appears in the vicinity of the yoke insulation contact face. The calculated maximum field strength value of the comb strut is 1.526106V/m; the minimum field strength value is 71180V/m; the ratio of the maximum and minimum field strength is about 21 times.

From the calculated maximum field strength values ​​of each solid insulation element, it can be seen that these calculated maximum field strength values ​​are much smaller than the breakdown field strength of each insulation member. At the same time, the calculated maximum field strength of the air in the model is 1.185106V/m, which is less than the initial discharge field strength of air. Therefore, from the calculation results, it can be seen that this type of dry-type transformer does not exhibit discharge and breakdown phenomena during the 1-minute power frequency test. Therefore, from the three-dimensional finite element analysis of the electric field at the end of the transformer, the insulation design of the end of the transformer can ensure the safety of the end insulation.