Criteria for the winding plan of hairpin windings to reduce the electric stress on the insulation in common mode

Abstract Due to the continuing development of power electronics and the increases in their voltage gradients, the electric insulation of the electric machines operated through an inverter is exposed to higher electric stress. After switching the power semiconductors, the potential distribution within the stator winding experiences a transient state in which the electric stress across the insulation reaches its maximum. In this paper, the maximum electric stress on the insulation is reduced without changing the geometry, material parameters or MMF distribution by utilizing degrees of freedom in the design of the winding scheme. For this purpose, the dependence of the conductor’s resistance and inductance, as well as its capacitance with respect to the stator core, on its position within the slot is investigated. In addition, the influence of the conductor’s electrical behavior on the maximum electrical voltage is analyzed. Based on this, criteria are derived for the arrangement of the conductors in the slots, compliance with which leads to a reduction in the maximum electrical load on the insulation. The result shows that the electric stress can be reduced by 21% if the degrees of freedom are utilized.