Sensitivity analysis of insulation state indicator in dependence of sampling rate and bit resolution to define hardware requirements

Industrial application of adjustable speed drives (ASD) has been constantly growing in the last decades. In addition to the sheer number of inverter-fed drives the variety of application fields is increasing too. The use of such ASD in safety critical devices or industrial systems with many drives installed leads to the requirement of increased reliability. Furthermore many drives are operated at or near their rated values to increase efficiency and return on investment. In comparison to mains-fed machines, high dynamics and the fast switching of the inverter adds significant stress to different components of inverter-fed drives. The electrical machine is one of the most important components in these drives. A major cause for machine breakdown is insulation related fault. It is important to mention that such faults do not occur suddenly but origin in an alteration of the insulation condition and finally lead to short circuits. This alteration of the insulation leads to changes in the machine´s high-frequency (hf) behavior. To reduce the number of breakdowns and apply predictive maintenance insulation monitoring can be implemented. Monitoring of the machine´s hf-behavior can be used to assess the insulation condition by investigation of the transients in the current or voltage. Thus oversampling of the sensor signals is needed. The needed sampling rate and resolution to detect alterations in the machine´s hf-behavior is investigated by experimental results.