Ageing Indicators of Stator Winding Insulation subjected to Elevated Frequency Voltage & Thermal Stresses

Laboratory studies were carried out to identify ageing indicators of stator winding insulation during ageing under elevated frequency, voltage and thermal stresses. A group of six generator bars was subjected to either electrical, thermal and combined electrical-thermal stresses. Electric stresses of 5kV/mm, 915 Hz and 6 kV/mm, 915 Hz and thermal stresses 170°C, 180°C and 200°C were chosen for the ageing studies. Combined electrical-thermal ageing studies were conducted at 5kV/mm, 915 Hz and 100°C. Evaluation study was conducted by electrical, thermo-analytical and spectroscopic techniques. The results are presented and discussed in this paper.