Application of dynamic mechanical analysis to endurance testing of generator stator bars

The thermal cycling test for generator coils and bars combines a modest increase in temperature cycling rates and cycle temperatures compared to normal operation. This test is performed on full size stator bars and coils and provides valuable data on the ability of the groundwall insulation to resist delamination and remain well bonded to the copper stack. To gain insight into the behavior of the resin component of the insulation system, dynamic mechanical analysis is proposed as a tool to aid in the development of thermally stable insulation systems for continuous high temperature operation and to support current efforts in determining the optimum parameters for thermal cycling tests. Flexural modulus and loss tangent measurements obtained by dynamic mechanical analysis represent a powerful and convenient way to ascertain mechanical properties and their evolution with temperature using microspecimens. Excellent correlation was demonstrated with flexural strength for homogeneous materials, over a broad temperature range