Étude des facteurs influençant le mécanisme des décharges partielles d'encoche

Abstract

Slot partial discharges (PD) which take place on bars closer to the high voltage terminals of the stator winding in the air gap between the magnetic iron core of the stator and the winding insulation, are recognized as being harmful to the groundwall insulation. In order to determine the effect of the different parameters that affect the evolution of slot DP and the insulation degradation mechanism, an extensive study has been initiated in 2007. This study was divided into three sections which have been the implementation of two laboratory aging experiments and the development of a PD model. A first accelerated aging laboratory experiment was conducted on six stator bars divided into three groups and subjected to slot DP under electrical stress alone, under electrical and thermal stresses and, finally under electrical, thermal and mechanical stresses. The aging experiment lasted for 25000 h and the changes in the detected phase resolved partial discharge patterns of slot PD were analyzed as a function of aging time for each stress condition while surface conductivity measurements as well as visual observations were carried out to complement the PD results. Subsequently, a secondary laboratory experiment was carried out using two stator bars placed in a climatic chamber and exposed to slot PD activity at two temperatures Under three aging sequences of 230 h at three different humidity levels. The phase resolved partial discharge patterns were monitored throughout each aging sequence and visual observations of the surfaces were made at the beginning and at the end, in order to characterize the evolution of slot partial discharge under each condition. At last, a numerical partial discharge model was developed in order to evaluate the effect of the surface condition on the electric field distribution inside an air cavity typical of the one where slot PD occur. Results confirm that insulation degradation mechanisms are dependent on the type of stress present but also on surface degradation (insulation and magnetic iron core). These parameters also significantly influence the evolution of slot PD and are usually interrelated. In addition, it was confirmed that the presence of the triple stress, namely electrical, thermal and mechanical is the worst condition and progresses much faster to cause failure than when only electrical and thermal stresses were actives and it is thus important to recognize this situation from the others.

Date	7 Aug 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Éric David (Supervisor) & Claude Hudon (Co-supervisor)