[Zurück]

T. Zika, A. Jagenbrein, F. Buschbeck, G. Preisinger, M. Gröschl:
"Electric phenomena in frequency converter-driven motors";
Vortrag: ÖTG-Symp. 2006, Steyr; 23.11.2006; in: "Proc. ÖTG-Symp. 2006", (2006), ISBN: 978-3-901657-23-8; S. 131 - 139.

Damages of rolling bearings caused by electric current passage are known for
decades [1]. The current paths for d.c. and low-frequency a.c. currents have
been studied and mitigating methods, such as insulated bearings and shaft
grounding brushes [2], have been developed. Because of the demand for precise
control and adjustment of the rotational speed of machines and, hence, of the
coupled electric drive, frequency converters have been designed to control the
rotational speed of three-phase induction motors [3]. However, with the introduction
of frequency converter drive systems, bearing failures due to electric current
passage have increased significantly. Because of the high slew rates of the signals
supplied by frequency converters, so-called dV/dt currents and related parasitic
effects arise [4]. To reduce these currents, mitigating measures have been
developed, such as common mode filters and chokes [5].
This paper gives a holistic overview on possible parasitic currents in electric drive
systems comprising a frequency converter, a three-phase induction motor and a
coupled machine. The basic electric properties of rolling bearings are summarised
and a typical electric drive system is described. Potential sources of parasitic
currents are explored and the impacts of the different current types on the
bearings are discussed. A new method to prevent bearing currents is introduced.

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