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P.W. Nussbaumer, M. Vogelsberger, T. Wolbank:
"Sensitivity Analysis of Insulation State Indicator in Dependence of Sampling Rate and Bit Resolution to Define Hardware Requirements";
Vortrag: 2013 IEEE International Conference on Industrial Technology, Capetown, Südafrika; 25.02.2013 - 28.02.2013; in: "Proceedings of IEEE International Conference on Industrial Technology (ICIT)", (2013), ISBN: 978-1-4673-4568-2; S. 392 - 397.

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.
Keywords- AC motor

http://publik.tuwien.ac.at/files/PubDat_223933.pdf