Finite element analysis of electrical stresses in the insulation system of rotating machines fed by static converters

Nowadays, thanks to the recent advances in semiconductor technology, variable frequency drives (VFD) can be implemented in high voltage rotating machines. However, such applications require new considerations both in design as well as manufacturing processes of insulation systems, in particular as to the stator winding. In practice, due to practical problems in electric field sensors, the addressed new electrical stresses can only be measured as for the tangential electric field component over a surface of the insulation system. Finite element methods (FEM) entitle manufacturer to have an accurate estimation of electric fields at arbitrary regions of a defined geometry. In this contribution, three dimensional models of stator winding including both roebel bar and multi-turn coil are developed to highlight the major differences of electric field distribution between two cases of a conventional power frequency supply and a converter-fed supply on the insulation system.