Impact of the polymerization process on the electrical behavior of different impregnation varnishes

The machine thermal class is the main dimensioning factor for the insulating materials. Three main categories of insulation may be distinguished in rotating machines: namely turn to turn, turn to ground and phase to phase insulation. Nevertheless, most of the data available are given at room temperature. Little is known on their behavior versus the temperature. A better knowledge of these materials appears therefore necessary. In this paper, electrical characterizations are performed on turn to turn insulation materials. Formettes samples are realized. The enamel wire is the same for all the samples under study but different impregnation resins and the polymerization processes and mechanisms are envisaged. Conduction current measurements versus the type of impregnation varnish are presented and discussed. Changes in both transient and steady-state currents are studied versus temperature (up to 200 degC). Since most of the varnishes are synthesized with similar polymers but following different polymerization routes, the differences may been attributed to the polymerization process. Huge values of the conduction currents are measured at high temperature and are directly related to the chemistry of the polymerization process.