Alijännitevaihtelut

Alijännitevaihtelut, known in English as voltage sags or voltage dips, are a common power quality issue. They refer to a temporary reduction in the RMS voltage of the electrical supply, lasting from half a cycle to a minute, and returning to normal afterwards. These sags are characterized by a decrease in voltage to between 10% and 90% of the nominal value.

The primary causes of alijännitevaihtelut include short circuits on the power system, the starting of large inductive loads like motors, and faults on adjacent circuits. When a fault occurs, it draws a large amount of current, which can cause a voltage drop across the impedance of the power lines and transformers. Similarly, when a motor starts, it requires a significant inrush current, leading to a temporary voltage dip.

The effects of alijännitevaihtelut can range from negligible to severe, depending on the magnitude and duration of the sag. Sensitive electronic equipment, such as computers, programmable logic controllers (PLCs), and medical devices, can malfunction or shut down. This can lead to process interruptions in industrial settings, data loss, and reduced product quality. In residential settings, lights may dim, and electronic appliances might reset.

Mitigation strategies for alijännitevaihtelut include the installation of voltage regulators, uninterruptible power supplies (UPS), and dynamic voltage restorers (DVRs). Improving power system fault clearing times and reducing system impedance can also help minimize the occurrence and impact of voltage sags. Understanding and addressing alijännitevaihtelut is crucial for maintaining reliable and stable power for modern electrical systems.