Overheating of primary and secondary coils of voltage instrument transformers

We deal with the numerical model of overheating of primary and secondary coils of voltage instrument transformer. Calculated values are compared with two different measuring methods - measuring with thermal sensors and calculation of heating from measured resistance. All calculations are solved in three operating conditions by rated voltage, thermal limiting output and rated voltage factor 1.9 Un according to IEC 61869-3 standard. In the paper is studied dependence between overheating and thermal transmittance. The article also deals with simple design of core, primary and secondary coil of voltage transformer with two secondary windings.