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The evaluation of lightning impulses with oscillations or overshoot near the peak suffers from the definition in the actual recommendation. The breakdown behaviour depends on the frequency of the oscillation and the amplitude. The results of a European Research Project have shown, that the influence of the superimposed oscillations can be described...
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Citations
... The filtering technique for lightning impulses lead to two different approaches, the residual filtering method separating the oscillations from the mean curve [14] and the global filtering. [15]. A problem for both methods is the correct reproduction of the test voltage factor shape of Fig. 3 by the characteristic of the filter. ...
The revision of the relevant recommendations allows to introduce new definitions of lightning impulse parameters. Experimental results have shown that the breakdown voltage of insulating materials depends on the frequency of the oscillations or overshoot near the peak and that this behaviour can be described by a test voltage factor k. Different procedures to evaluate the test voltage and the time parameters of a lightning impulse voltage are described. Filtering methods leads to very good results in determining the test voltage, but at the moment differences exists in the determination of the time parameters of a lightning impulse. The time to peak of a switching impulse can also be determined more accurate by a procedure similar to lightning impulses. The new definitions seems not to influence the results of impulse tests on insulation systems but they contribute very much to the reproducibility of the tests results.
Transmission and distribution of electrical energy involves the application of high-voltage apparatuses like power transformers, switchgears, surge arrestors, insulators, power cables, transformers, etc. They are exposed to high transient voltages and currents due to internal and external overvoltages. Before commissioning, they are therefore tested for reliability with standard impulse voltages or currents. Depending on the apparatus and its proposed application, the specifications prescribe different types of test impulses, e.g., lightning, switching and chopped impulse voltages as well as exponential, rectangular and short-time alternating currents. For on-site voltage tests, oscillating lightning and switching impulse voltages are specified in addition. The standard impulses are defined by their test voltage value (or test current value) and at least two time parameters, with tolerances during generation and uncertainties during measurement. The background and specification of the new evaluation procedures in IEC 60060 concerning overshoots and oscillations superposed on lightning impulse voltages are treated in detail. This includes the presentation of the frequency-dependent test voltage function k(f) and the filtering method, obtained both as the result of world-wide round-robin tests. In the latter part of this chapter, fundamental circuits for generating high-voltage and high-current impulses are given, e.g., the multi-stage Marx generator for generating impulse voltages of up to several megavolts and the impulse current generator with crowbar gap arrangement for preventing undershoots of impulse currents.
Bei der Übertragung und Verteilung elektrischer Energie werden Betriebsmittel eingesetzt, die hohen transienten Spannungen
und Strömen ausgesetzt sind. Sie werden daher vor ihrem Einsatz mit genormten Stoßspannungen oder Stoßströmen auf ihre Zuverlässig-keit
geprüft. Hierbei unterscheidet man zwischen vollen und ab-geschnittenen Blitzstoßspannungen, Schaltstoßspannungen, Steils-toßspannungen
und schwingenden Stoßspannungen sowie zwischen Exponential- und Rechteck-Stoßströmen und Kurzschlusswech-selströmen. Die mit
Digitalrecordern aufgezeichneten Zeitverläufe sind durch mehrere Parameter mit Toleranzen bei der Erzeugung und mit Unsicherheiten
bei der Messung definiert. Für die Auswertung von Blitzstoßspannungen mit überlagerter Scheitelschwingung kommt ein genormtes
Filterungsverfahren zum Einsatz, mit dem der Prüfspannungswert und die Zeitparameter bestimmt werden. Ver-schiedene Generatorschaltungen
für Stoßspannungen und Stoßströmen werden prinzipiell beschrieben. Auch in anderen Berei-chen von Physik und Technik treten
hohe impulsförmige Spannun-gen und Ströme mit Zeitverläufen im Nano- bis Millisekundenbe-reich auf, die für eine Reihe von
Anwendungen in der Plasmaphysik, Medizin- und Schweißtechnik und bei Elektroimpulswaffen oder elektronischen Zündsystemen
genutzt werden.
