In low-voltage power systems, measurement and control systems, and computer networks, there are many factors that can cause surge overvoltages.
First, direct lightning
Lightning directly discharges the building with external lightning protection device or directly discharges the device on the top of the building that can transmit lightning current into the ground by some means (such as outdoor antenna, satellite receiving device, etc.), so that the ground potential rises, a large Part of the lightning current enters the building's equipment and connected equipment through the protective ground to form a surge overvoltage.
Second, the lightning strike nearby
Even if the building itself is not struck by lightning, nearby lightning strikes can cause surges on the building's installation. This surge overvoltage reaches the line of the electronic device or device either directly or through inductive or capacitive coupling. Part of the lightning current may be transmitted to the grounded device through the earth, causing great harm, or the electromagnetic field radiated by the lightning discharge channel, induces an overvoltage on the line of the equipment, and the long wire loop in the building is particularly easy to sense. Voltage. Capacitive coupling is produced by an electric field between two points with a high voltage difference, such as between a lightning discharge channel and a metal wire.
Third, lightning strikes in the distance
Lightning strikes hundreds of meters away may also induce overvoltages on low voltage conductors, data, or conduct high voltages to the grounding devices of buildings, causing significant damage to electronic equipment, even between clouds or clouds. The electromagnetic field generated by the discharge can also couple the surge overvoltage into the wire.
Fourth, the switch surge
Switching surges come from closed and open switching operations of the circuit, switching operations from inductive and capacitive loads, and also from short-circuit current blocking, especially in large power systems or transformer disconnections that may cause proximity to nearby electronic equipment. Damage.