Verfahren zur Überspannungsreduktion an wechselrichtergespeisten Maschinen - Das Schirmabschlussverfahren (English shop)

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Steep switching edges lead to asymmetric voltage distributions within the winding system of an electrical machine. In combination with long motor cables, travelling-wave reflections can cause overvoltages of several times the DC link voltage at the machine terminals. Both problems are superimposed, so that insulation damage as a result of a series of partial discharges is to be expected if the insulation quality is inadequate. Common-mode currents, caused by an asymmetric system, can likewise damage the drive system.

Various existing countermeasures are presented and explained in more detail. The innovative shield termination method is based on establishing reflection conditions on the motor side, so that travelling waves reflected on the inner conductors of individually shielded motor cables are cancelled by the negatively coupled voltages of the forward-travelling waves of the shields. For this purpose, the shields are terminated on the machine side, while the shields on the inverter side remain open. The method is proven theoretically and verified by experiments. A comparison with countermeasures already presented reveals the advantages and disadvantages. Furthermore, design rules relevant to practical application are stated.