What are the main causes and basic types of surges?

Surges in electrical installations are divided into two groups:

• internal surges,
• external surges.

This division relates to causes of these surges.

Internal surges take place inside electrical installations, e.g. as a result of switching currents, damage to electrical installation or sudden load change. They are further divided into:

• connection surges, which take place during switching unloaded lines on and off, as well as during automatic elimination of short-circuits;
• occasional surges, which are caused as a result of sudden load change;
• short-circuit surges, they include short-circuits to the ground;
• resonance surges.

The second group includes atmospheric surges caused by environmental phenomenon, mainly by atmospheric discharges. Their division depends on the distance from electrical installation. The strongest surges are caused when a lightning directly strikes electrical installation. In the second place there are surges caused when a lightning strikes in close proximity to electrical installation. Atmospheric discharges that take place between clouds are less significant; of course, the closer the distance to electrical installation, the stronger the discharge. Atmospheric discharges can also be caused by radio waves.

Division of surges can also be based on their duration: they can be pulsed or long-lasting.