Dielectric stresses determination in active part of the combined transformer

Insulation system of instrument transformers is exposed to various dielectric stresses that can be hazardous if the dielectric strength of insulation is exceeded. Electric field strength depends on the voltage distribution along the active part which has been calculated using Electromagnetic Transients Program (EMTP). This paper gives comparison of calculated voltage distributions and measurements made on a real transformer. The results obtained by these investigations enable optimization of active part of combined transformers, and can be used in instrument transformer design