Study on electric field distribution and dielectric loss characteristics of insulation gap in dry-type transformer based on finite element method

Dry-type transformers are widely used in modern power systems because of their safety and reliability, and their insulation performance directly affects operational stability and service life. Existing studies mainly focus on electric-field breakdown of insulation structures, while dielectric loss caused by insulation gap variations has received less attention. This study develops a two-dimensional axisymmetric finite-element model of the main insulation of a 10 kV dry-type transformer. It investigates how the LV-HV gap and the Fe-LV gap affect electric-field distribution. The active/reactive power method is used to extract volume loss density and terminal complex current, calculate the equivalent dielectric loss factor of the main insulation, and analyze the effect of the LV-HV gap on dielectric loss. Within the simulated conditions, the LV-HV gap strongly affects field intensity and dielectric loss: reducing it from 21 mm to 13 mm at power frequency increases the equivalent dielectric loss by about 52.5%, whereas the Fe-LV gap has a negligible effect. For the three LV-HV gaps examined (13, 17, and 21 mm) at power frequency, an empirical power-law correlation is fitted. Since it is based on only three data points, it should be treated as a local interpolation rather than a validated quantitative law and should not be extrapolated. The study examines the chain “insulation gap–electric-field distribution–dielectric loss” in terms of peak field, field distribution, and energy integration. It also highlights the role of field uniformity in dielectric loss regulation. These results provide theoretical and simulation support for multi-objective optimization of dry-type transformers, balancing electrical strength, volume, and operational loss. All results are from 2D finite-element simulations at 10 kV and have not been experimentally validated; the conclusions are therefore provisional and limited to the studied conditions.