Dry Type Transformer Rating Is a Thermal Calculation You Can Verify
By Xinya Power editorial team
Dry Type Transformer Rating Is a Thermal Calculation You Can Verify
A dry type transformer replaces liquid insulation with air and solid dielectrics, and every nameplate number descends from that choice. The governing standard is IEC 60076-11, applied in China as GB/T 17467 for systems up to 72.5 kV. The rating logic is thermal: insulation class sets the ceiling — F tolerates 155 °C, H 180 °C — and average winding temperature-rise limits follow, about 100 K for F and 125 K for H, verified by resistance measurement, not surface probes. The gap between rise limit and insulation ceiling is the working margin, so a datasheet showing only efficiency hides the figure that matters. Two constructions dominate. Vacuum-cast epoxy windings tolerate humidity and long idle periods with minimal maintenance; open-wound vacuum-impregnated windings cost less and accept rework but expect clean dry rooms. Enclosure choice follows use: IP20 indoors, IP23 against dust and weather. Natural air gives the base rating; forced fans add roughly a third to a half more capacity, sized for summer peaks rather than continuous duty. Harmonics add a final check, because extra eddy losses heat windings without changing nameplate current. Read the thermal figures first.
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