Study on the Distribution of Internal Stress in the Curing Process of Insulation Layer of Dry-type Transformer Winding

Dry-type transformer shows a good application prospect because of its advantages of safety, easy maintenance and flexible use. In the actual production process, the insulation layer of dry-type transformer coil winding is easy to produce defects such as stress concentration and microcracks, which have an important impact on the performance and life of dry-type transformer. In this paper, the temperature rise, curing degree distribution and stress distribution of dry-type transformer winding insulation layer during curing are simulated. The simulation results show that the curing rate of epoxy resin with different insulation layers is obviously different. When the insulation material of winding is thermally cured for 6 h, the curing degree of the third layer of high-voltage winding is 91.1 %, which is 12.3% higher than that of the third layer of low-voltage winding. Through the stress nephogram, it is calculated that the volume stress and surface stress at the bottom of the epoxy resin insulation layer are 30.8 MPa and 29.9 MPa respectively, while the volume stress and surface stress at the middle of the insulation layer are 5.9 MPa and 7.2 MPa respectively. This shows that the stress distribution of high voltage winding is uneven, and the thermal stress concentration phenomenon will appear at the bottom of its insulation layer. The research in this paper will provide technical support for the production process optimization of high voltage grade and large capacity dry transformer.