Assesment of aging in HV electrical machine insulation with the help of partial discharge monitoring

Aging of electrical machine insulation is influenced by electrical, thermal, mechanical and environmental stresses during the operation. The mechanical, thermal and resulting thermomechanical processes have an excessive influence on the service life of the insulation.Partial discharges can cause erosion of insulation material and accelerate aging processes. On the other hand, they give informations about the insulation condition and degradation mechanism of the insulation.PD analysis is an effective tool for studies of the aging processes. The aim of pd monitoring is assessment of the aging phase and fault development of the insulation. This paper presents results of the pd-monitoring during long term aging experiments on the HV electrical machine insulation to examine mechanisms which could degrade a stator insulation.The test bars are exposed to accelerated aging tests. Combined electrical (8.75 kV/mm), thermal (20, 90, 130OC) and mechanical stresses (vibration) are applied to the samples, and the partial discharge measurements are done daily and automatically on them.Post data processing of the recorded pd signals shows. a correlation of the pd activity with the aging level of the insulation and the degradation mechanism during the accelerated aging tests can be found more exactly.