Assessment of Edgewise Insulated Wire Bend Radius Impact on Dielectric Properties of Turn-to-Turn Insulation Through Thermal Aging

This study aims to evaluate the impact of the bending radius of edgewise insulated wires on dielectric properties such as partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV), dielectric dissipation factor (DDF), and insulation capacitance (IC) through thermal aging. The tests are performed at room temperature (20 °C) and atmospheric pressure (1013 mbar) on unaged and thermally aged polytetrafluoroethylene (PTFE)-wrapped pairs of edgewise insulated wires, models of the turn-to-turn insulation. The accelerated thermal aging is carried out at 250 °C (i.e., 50 °C higher than thermal class) for two different aging periods: 156 and 312 h. To manufacture a coil, it is generally demanded to shape 90° bends out of edgewise enameled winding wires. Therefore, the obtained experimental results are helpful for the coil manufacturers, providing a clue how the bending radius can impact the dielectric properties of turn-to-turn insulation and introducing an optimum radius, which can present better insulation performance.