On the area of adjustable-speed drives the importance of pulsewidth modulated inverters is permanently increasing. Because ofconnecting cables between such inverters and motors on the one hand andpulses with steep-fronted voltage waveforms on the other hand there areovervoltages at the motor terminals and a nonlinear distributed phasevoltage, both additional deterioration factors for the motor insulation.Since the prevailing cause of this deterioration are partial dischargesthere is a need for to have insulation materials with a high partialdischarge inception voltage and a high resistance to such discharges. Inthe first part of this paper a new developed wire enamel is presented onthe basis of several investigation results as endurance behavior underinverter pulse conditions as function of thickness, structure,composition, mechanical prestress in comparison to traditional enamels.In the second part of this paper the influence of impregnating materialsand procedures on the partial discharge behavior and lifetime isdemonstrated. The applied samples were twisted pairs of enameled wiresand motorettes, respectively. At these investigations a new createdmeasuring technique for partial discharge indication was employed, ableto detect discharges under inverter pulse conditions, not possible withpertinent commercial devices
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