Time-to-Breakdown of Electrical Insulation in Electric Machines for Aviation

Electrical propulsion is a possible propitious path in aviation for reduction of CO₂ emissions. For this, power density needs to be increased, which can be achieved by increasing the voltage in the drivetrain. When increasing the voltage, partial discharges (PDs) arise and become detrimental to reliability and lifetime of the insulation system. In this work, voltage endurance tests with PDs present have been conducted with both sinusoidal voltage and bipolar switched voltage with rise time of sub- 100 ns. The results at 2.5 kVpk show that time-to-breakdown is following the number of voltage cycles in the tested frequency range from 50 Hz to 50 kHz, disregard of the voltage shape. Increasing the voltage to 6 kVpk reduces the time-to-breakdown more with switched voltage than sinusoidal by a factor 14. Hence, both higher slew rate and switching frequency can have a detrimental effect on the lifetime of electric machine insulation systems.