Članek obravnava modeliranje srednjenapetostnega podpornega izolatorja. V programskem orodju Matlab je izdelan model izolatorja, nato je izveden izračun električnega polja v programskem orodju Elefant. Poudarek je namenjen zunanji obliki izolatorja. V članku so prikazani primeri izolatorja z različnim številom reber in njihov vpliv na električno polje izolatorja.The paper describes the designing of a medium voltage post insulator. The insulator model was designed in Matlab software and calculations of the electric field were in Elefant software. The emphasis is on the external shape of the insulator. The paper presents examples of the insulator with different number of ribs and their influence on the insulator’s electric field strength