Frequency domain considerations

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Amplitude spectrum

The frequency spectrum of the LEMP is also of interest, especially for RF applications. It reaches several 100 kHz (NEMPs about the thousandfold). This is important for certain lightning protection solutions in RF engineering applications described later.

The diagram shows the comparison of the frequency spectra of a genuine lightning current surge (blue according  to K. Berger) and a test current surge 10/350 µs (red according to IEC 61312-1)

The diagram gives evidence of the 10/350 µs test pulse meeting the direct lightning interference best. This is considered in IEC 61024-1 "Protection of structures against lightning". Therefore, it is most suitable to test protection devices. HUBER+SUHNER test their lightning protectors/EMPs according to this pulse in regard to the lightning current resistivity (also called current handling capability).

IEC 61312-1 defines a combined 1.2/50 µs voltage and 8/20 µs current test pulse for surge protection devices to determine their protection performance. Despite it is more relevant for general induction and power switching interferences, this pulse is also used for the description of the protection quality of lightning protectors/EMPs worldwide. Protection performance data show the residual pulse left behind a protector when fed with a 1.2/50 µs; 8/20 µs combination generator pulse.