| Abstract |
At inverter-fed traction drives stray currents due to parasitic capacitances in frequency converters andmachine cause high frequency voltage components spreading into all conductive components of thedrive system. These hf voltages are harmful and origin from the inverter side through fast switchingpower semiconductors with high levels of output voltage steepness. Additionally overvoltage at themachine occurs by inverter operation of the machine and is thus stressing the machine insulationsystem. These effects can lead to a reduction of the machine insulation lifetime due to loss ofinsulation strength. Thus, insulation condition monitoring systems are necessary to enable a safe andreliable operation of a drive. Insulation condition monitoring of inverter-fed traction drives isimplemented in this work by evaluating the transient current response after voltage step excitation.The current measurement is performed using the built-in current transducers of the inverter, normallyused for the control of the drive, to save cost and space. Insulation degradation usually is a slowlydeveloping process, at which the parasitic capacitances of the winding system change and thus also thetransient current response. However, influences from the inverter capacitances cannot be neglectedand thus the influence of the parasitic capacitances located in the inverter on the proposed insulationcondition monitoring is investigated. |
