Low-frequency dielectric response of epoxy-mica insulated generator bars during multi-stress aging

The aging of insulating materials and insulating systems involves physical and/or chemical changes of the insulating material. These changes in turn lead to changes in the dielectric response of the insulating system. Quantitative measurements of the dielectric response function can be performed using either time or frequency domain techniques, both being mathematically related for linear systems. To investigate the evolution of the low-frequency dielectric response of epoxy-mica rotating machine insulation winding system as a function of aging, time domain dielectric measurements were conducted before, during and after a multi-stress aging program, using a full scale accelerated aging test facility. The results obtained in the investigation are reported in this paper. Modeling of the low-frequency dielectric response is also presented in this paper, with the model having been found to be in good agreement with the experimental results