F204AC-63SLASH0.1 datasheet(5/62 Pages) ABB

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1SXU000023C0202 Rev. A

Overvoltages due to direct lightning strikes

These can take two forms:

• When lightning strikes a lightning conductor or the roof of a building which is grounded, the lightning current is dissipated into the ground.

The impedance of the ground and the current flowing through it create large difference of potential: this is the overvoltage. This overvoltage

then propagates throughout the building via the cables, damaging equipment along the way.

• When lightning strikes an overhead low voltage line, the strike produces high currents which penetrate into the building creating large

overvoltages. The damage caused by this type of overvoltage is usually catastrophic (e.g. fire in the electrical switchboard causing the

destruction of buildings and industrial equipment) and results in explosions.

Direct lightning strike on an overhead line

Direct lightning strike on a lightning conductor or the roof of a building

General information

General points on lightning and its risks

Overvoltages due to the indirect effects of lightning strikes

Overvoltages are also produced when lightning strikes in the vicinity of a building, due to the increase in potential of the ground at the

point of impact. The electromagnetic fields created by the lightning current generate inductive and capacitive coupling, leading to other

overvoltages. Within a radius up to several kilometers, the electromagnetic field caused by lightning in clouds can also create sudden

increases in voltage.

Although less spectacular than in the previous case, irreparable damage is also caused to sensitive equipment such as fax machines,

computer power supplies and safety and communication systems.

Magnetic field

Increase in ground potential

Electrostatic field

F204AC-63/0.1 Datasheet(PDF) 5 Page - ABB