Effects on electrical installations
Lightning damages electrical and electronic systems in particular: transformers, electricity meters and electrical appliances on both residential and industrial premises.
The cost of repairing the damage caused by lightning is very high. But it is very hard to assess the consequences of:
- disturbances caused to computers and telecommunication networks;
- faults generated in the running of programmable logic controller programs and control systems.
Moreover, the cost of operating losses may be far higher than the value of the equipment destroyed.
Lightning stroke impacts
Lightning is a high-frequency electrical phenomenon which causes overvoltages on all conductive items, especially on electrical cabling and equipment.
Lightning strokes can affect the electrical (and/or electronic) systems of a building in two ways:
- by direct impact of the lightning stroke on the building (see Fig. J5 a);
- by indirect impact of the lightning stroke on the building:
- A lightning stroke can fall on an overhead electric power line supplying a building (see Fig. J5 b). The overcurrent and overvoltage can spread several kilometres from the point of impact.
- A lightning stroke can fall near an electric power line (see Fig. J5 c). It is the electromagnetic radiation of the lightning current that produces a high current and an overvoltage on the electric power supply network. In the latter two cases, the hazardous currents and voltages are transmitted by the power supply network.
- A lightning stroke can fall near a building (see Fig. J5 d). The earth potential around the point of impact rises dangerously.
In all cases, the consequences for electrical installations and loads can be dramatic.
The various modes of propagation
Common-mode overvoltages appear between live conductors and earth: phase-to-earth or neutral-to-earth (see Fig. J7 ). They are dangerous especially for appliances whose frame is connected to earth due to risks of dielectric breakdown.
Differential-mode overvoltages appear between live conductors:
phase-to-phase or phase-to-neutral (see Fig. J8). They are especially dangerous for electronic equipment, sensitive hardware such as computer systems, etc.