Progress on IEC 60034-18-42 for Qualification of Stator Insulation for Medium-Voltage Inverter Duty Applications

There is an industry need for suitable methods to qualify medium-and high-voltage stator insulation systems for inverter duty applications. Technical Specification (TS) IEC 60034-18-42 is being written to address the unique requirements of form-wound micaceous systems to withstand inverter pulses, characterized by elevated voltage, fast rise times, and high frequency impulse repetition rates. These machines do not operate under the same ageing conditions as those supplied by sinusoidal power or as random windings supplied by pulse-width modulated (PWM) drives. Depending on the specific waveform characteristics observed at the machine terminals, the ground wall insulation, turn insulation, corona suppression and end winding voltage grading systems are significantly affected by ageing factors such as partial discharge (PD) and elevated temperature. The TS offers technically sound guidelines to manufacturers and users describing test procedures to prove the electrical and thermal reliability of these components. Like IEC 60034-18-41 (for low voltage systems) it will significantly impact construction and testing of NEMA motors. This paper describes the theoretical and practical considerations of the specification.