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Overvoltage protection is the process of securing an electrical system from the possible damages that may be caused by overvoltage through the use of devices like arcing horns attached to transmission lines and Zener diodes for electronic circuits. Overvoltage is a condition wherein the voltage in a circuit quickly jumps to its upper design limit owing to a phenomenon like a power surge from lightning strikes.
Overvoltage protection is an essential part of any electrical and electronic system. It ensures that the system runs as designed and undamaged despite changes in external conditions, specifically those that cause overvoltage and power surges. Typical causes of overvoltage include natural events such as lightning strikes, man-made sources such as inductive loads like motors and electromagnets, and electromagnetic pulses. All of these cause the voltage and current level within a circuit to spike, which may damage some of its parts, and for electronic circuits requiring only miniscule amounts of voltage, a spike could fry most of the sensitive components like the microchips.
In bigger electrical systems like the power grid itself, there must also be a good level of overvoltage protection. In high-tension transmission lines, for example, events such as a power surge or overvoltage can cause the electric field to exceed the dielectric strength or resistivity of air, causing electricity to arc between conductors or wires and over the insulators. This causes extreme flashes of heat that could melt the insulators and damage the wire; it also causes short circuits. In this case, arcing horns are installed on areas susceptible to arcing as they provide near infinite impedance, ensuring that power surges and overvoltage do not cause trouble.