LIGHTNINGS and TRANSIENTS

Users of electronic equipment and communications and information technology systems must keep their equipment in operation even though lightning strikes could cause momentary voltage spikes on power supply and data lines.

There are several reasons for this:

• The electronic components used make these systems more susceptible to failure.
• Costly service interruptions are unacceptable.
• Data transmission networks extend over long distances and areas and are subject to more interference.

Lightning strike

Blitzschläge, die seit den ersten Untersuchungen von Benjamin Franklin im Jahr 1749 Gegenstand der Forschung sind, haben sich zu einer wachsenden Bedrohung für unsere von elektronischen Geräten abhängige Gesellschaft entwickelt.

Emergence of lightning

Lightning occurs between two oppositely charged zones in the atmosphere, typically between two thunderclouds or between a cloud and the ground. It can travel over several kilometers in successive jumps to the ground, with a guide flash first causing a highly ionized lightning channel. Only when this reaches the ground does the actual flash or main flash occur. Then a current of several tens of thousands of amperes flows through the ionized channel from the ground to the cloud or vice versa.

Fig. 1 - Positively charged ice crystals are at the top of the thundercloud, negatively charged water droplets at the bottom.

Fig. 2 - Negative charges in the guide flash first toward the ground, where charge redistribution occurs.

Fig. 3 - The guide flash is met by a positive discharge from the ground.

Fig. 4 - Charge carriers move between thundercloud and ground in the main flash.

Fig. 5 - The lightning has exchanged charges between the cloud and the ground. The ground is now more negatively charged than before.

Direct effects

At the time of discharge, a pulse current flows with a peak value between 1,000 and 200,000 amperes and a rise time of a few microseconds. The direct effects lead to damage to structural installations through mechanical damage or even a fire. The best protection is still provided by the classic lightning conductors or lightning protection systems, which are designed to "capture" the leakage current and feed it to a specific point.

Indirect effects

The direct effects of a lightning strike in structural facilities hit their electrical and electronic systems in particular. High lightning currents lead to high potential rises and high voltage differences that can easily damage electrical equipment.