Separation of disturbing influences on induction machine´s high-frequency behavior to ensure accurate insulation condition monitoring

The range of industrial applications requiring adjustable speed drives (ASD) is continuously increasing. Although generally highly reliable, a breakdown of an electrical machine has to be prevented under any circumstance for certain applications like safety-critical devices or industrial systems with many drives installed. To increase efficiency and return-on-investment the drives are operated at or near their rated values. High dynamics, overload and the fast switching of the inverter cause additional stress for the different drive components. One of the major causes for drive breakdown is insulation deterioration. Before an actual breakdown of the insulation system occurs, the machine´s high-frequency behavior is altered. Therefore monitoring of the drive´s hf-behavior can be employed to evaluate the insulation condition. However, other drive components like cabling, grounding or the inverter may change the drive´s hf-behavior as well. The possibility to separate the different influences of the machine´s hf-behavior is thus essential and will be shown by experimental results.