afstandsrelæ

An afstandsrelæ, or distance relay, is an electrical protection device used primarily in power systems to safeguard transmission lines and generators from faults such as short circuits or overloads. It operates based on the principle of measuring the impedance or distance between the relay and the fault location along a transmission line. By comparing measured impedance with predefined thresholds, the relay determines whether a fault exists and whether it lies within its protected zone.

Distance relays are essential in high-voltage power systems because they provide selective and rapid fault clearance, minimizing damage to equipment and reducing downtime. They are typically installed at substations and work in conjunction with circuit breakers to isolate faulty sections of the network. The relay’s response time is critical, as delays can lead to cascading failures or equipment damage.

Modern afstandsrelæs incorporate advanced algorithms, such as mho, reactance, or offset mho characteristics, to improve accuracy and reduce misoperations. These algorithms account for variations in line parameters, such as resistance, reactance, and loading conditions. Some relays also feature directional elements to distinguish between faults occurring in the forward (protected) direction and reverse (unprotected) direction, enhancing selectivity.

Distance relays are often combined with other protection devices, such as differential relays or overcurrent relays, to form comprehensive protection schemes. They are programmed and calibrated based on system parameters, including line length, impedance, and fault levels. Regular testing and maintenance ensure reliable operation, as environmental factors or component aging can affect performance.

Applications of afstandsrelæs extend beyond transmission lines to include generator protection, busbar protection, and motor protection. Their versatility and precision make them a cornerstone of modern power system protection strategies.