Ylijännitteenrajoittimet

Ylijännitteenrajoittimet, known in English as surge arresters or lightning arresters, are crucial electrical devices designed to protect electrical equipment from overvoltage transients. These transients can be caused by lightning strikes, switching operations within the power system, or other sudden electrical disturbances. The primary function of an ylijännitteenrajoitin is to divert the excess energy of these overvoltages to the ground, thereby preventing damage to sensitive components like transformers, generators, and insulators.

The operation of an ylijännitteenrajoitin is based on its ability to exhibit very high resistance under normal operating voltage conditions, effectively acting as an insulator. However, when the voltage across it exceeds a specific threshold, known as the breakdown voltage or sparkover voltage, its resistance drastically decreases. This sudden decrease in resistance allows the surge current to flow through the arrester to the ground. Once the overvoltage event has passed and the voltage returns to normal levels, the arrester's resistance increases again, interrupting the flow of current and restoring the system to its normal operating state.

There are several types of ylijännitteenrajoittimet, with metal oxide varistors (MOVs) and silicon carbide (SiC) arresters being among the most common. MOVs utilize a semiconductor material whose resistance varies non-linearly with voltage. SiC arresters, on the other hand, employ silicon carbide disks. The selection of the appropriate ylijännitteenrajoitin depends on factors such as the system voltage, the expected surge levels, and the required protection characteristics. Proper installation and maintenance are essential for ensuring their effectiveness in safeguarding electrical infrastructure.