Electrical ageing test on random wire wound stator insulation applying voltage pulses

The adoption of switching electronic converters for squirrel cage motor drives can lead to some critical issues during the normal operation. The early failure of the stator winding insulation is one of the most investigated problems. The cost of motor failure is measured by interruption of plant output as well as extent of repair or replacement. The Surge Test is one of the most important tests for industrial electric motors, insofar as it allows the accurate checking of the machine functionality in order to identify any possible fault in the windings. Surge test is non-destructive and it has to be conducted at test voltage amplitudes so that they do not produce any winding damage and any significant insulation system degradation. This research presents the outcome of an experimental campaign in order to investigate the role of the voltage pulses on the degradation of the stator winding insulation of Type I electric motors: during the study the inter-turn, the groundwall and the phase-phase insulation systems have been taken into account. Electrical aging test have been performed using a surge test waveform at the terminals of the windings. Suitable electrical parameters have been monitored in order to identify the life end conditions. The amplitude of the applied voltage have been varied and the life time values have been collected and analysed. Furthermore the correlation between the repetitive partial discharge inception voltage and the life time has been investigated.