Characterization of Insulation Material Parameters in Low-Voltage Electrical Machines

In inverter-driven low-voltage electrical machines, the insulation system is stressed by steep voltage slopes. In many applications, the use of silicon carbide-based semiconductors and an increase in the DC link voltage are desired. These trends reinforce the risk of partial discharges which are mainly triggered by high electric fields. Material parameter such as the permittivity and the thickness of the insulation layer influence the electric field inside the insulation system. To determine the permittivity, capacity measurements are carried out on enameled wires. Besides, the cross-section of the wires is analyzed to measure the insulation thickness allowing the calculation of the permittivity based on a cylinder capacitor geometry. To study the influence of these parameters, the Townsend equation is used to determine the expected partial discharge inception voltage. By comparing the simulation results to partial discharge measurements on twisted pair samples, the secondary-electron-emission coefficient can be determined.