Stator insulation monitoring of inverter-fed machines based on current transient evaluation

In this paper, a concept for the condition monitoring of the stator insulation of electrical machines is described using the transient current evaluation. In electrical traction applications, the motor is operated via a voltage source inverter which supplies the machine with voltage variable in frequency and amplitude. The inverter-fed drive system can be described in principle by three main components: the inverter, the cabling and the machine, which define a complex impedance system. The motor and inverter represent separate functional units, which are designed separately. Inverter and machine are connected via the supply lines. If a critical cable length is reached reflection phenomena and overvoltages occur. After describing the components and their interactions, the principle of the monitoring method is presented and verified on a test machine. Experiments with artificially aged winding systems describe the relationships between the change in the transient current signals and the loss of the insulation properties in the winding system.