The foreseeable addition of anhydrides to the REACH (regulation on the registration, evaluation, authorisation and restriction of chemicals) directive of potentially harmful materials urges manufacturers of rotating high-voltage machines with anhydride-based insulation systems to find suitable replacements. Such significant changes in the insulation systems require qualification steps, including an accelerated thermal ageing test e.g. according to IEC 60034-18-31. The standard pursues the objective to assess insulation systems regarding the ability to withstand thermal ageing over the targeted operational lifetime. Therefore, cyclic tests consisting of thermal, mechanical and ambient stress are carried out. Thermal stress is the main ageing source during the qualification and is used to determine the thermal lifetime curve of the insulation system. For a successful qualification, the thermal lifetime curve of a candidate system must be equal to or succeed the one of a reference system with sufficient operational experience. Even though IEC 60034-18-31 is referred to as an accelerated thermal classification, it constitutes a tremendous spatial and temporal expense. Practical experiences and considerations regarding the test voltage level and mechanical stress are discussed in the context of specimen design and total duration of the investigations.