A Proposition for Improving the Design of Motor Windings for low-Pressure Environment

In low-pressure environment, partial discharges (PDs) appear for lower voltages, shortening strongly the machines life times fed by PWM inverters. A new approach is proposed for designing AC motor windings free of PD at low pressure. The method consists of adding a thin resistive layer on the outer surface of the enameled wire used for winding the machine. Thereby, PDs occur only in critical zones, near the wire connections, rather than randomly in coils. Consequently, a coil design with a small additional quantity of varnish in critical zones can increase strongly the partial discharge inception voltage (PDIV). The paper proposes a theoretical analysis of the improvement based on Paschen's law for its application in non homogenous electrical fields.