Analysis of localized dissipation factor measurements on the insulation system of mechanically aged generator stator bars

Integration of decentralised renewable energy sources lead to an increasingly fluctuating load profile of power engineering equipment. In particular, on large rotating machines this changing load profiles continuously stress the insulation in form of mechanical and thermo-mechanical forces. Eventually, a mechanical overstressing can ultimately result in an electrical breakdown of the insulation. To evaluate the condition of electrical insulation systems the knowledge of predominant aging mechanisms is of particular importance. This paper presents accelerated multi-factor aging tests with simultaneous mechanical and thermal loads on generator stator bars. Localized dissipation factor measurements as well as partial discharge detection are performed between aging cycles. An interrelationship between mechanical stress and the results of experimental examinations is indicated and analyzed. It can be shown, that mechanical stress can lead to cracking of the insulation, which is verified by the use of computer tomography.