Electrical discharge in enamel-insulated, hairpin copper conductors

Polyimide-based enamel insulation is widely used on conductors that are employed in electric motors. Thus, the integrity of enamel insulation is extremely critical for the healthy operation of the motor. If the enamel insulation fails to isolate two neighboring conductors in an electric motor, a short circuit will occur that may possibly lead to the failure of the motor through a sequence of events. During the manufacturing of the windings of an electric motor, enamel-insulated copper conductors may be subjected to mechanical strain. This strain may adversely affect the electrical performance of the enamel insulation. Under the influence of an electric field, partial discharge in the insulated conductors may occur as one of the initial mechanisms that may eventually cause the insulation failure. Therefore, in order to predict the long term behavior of the enamel insulation, it seems to be sensible to quantify the partial discharge behavior of the enamel insulated conductors used in motors. Within the scope of this study, copper conductors having hairpin structures with rectangular cross-section in carbon powder were investigated and compared for their partial discharge behavior as well as breakdown voltages. Although the average partial discharge inception voltage (PDIV) and partial discharge extinction voltage (PDEV) with conductor samples formed in the hairpin structure appeared to be closer to those of the unstrained, straight conductors investigated in our earlier study, the breakdown voltages (BDV) for conductors with hairpin structure were significantly lower than those of straight conductors.