Überstromrelais

An Überstromrelais, or overcurrent relay, is a protection device used in electrical power systems. Its primary function is to detect excessive current flowing through a circuit and initiate a protective action, typically by tripping a circuit breaker. This action is crucial for preventing damage to electrical equipment such as transformers, generators, and transmission lines, as well as for ensuring the safety of personnel.

Overcurrent relays operate based on sensing the magnitude of current. When the current exceeds a predetermined threshold, known as the pickup setting, the relay activates. There are different types of overcurrent relays, broadly categorized by their time-current characteristics. Instantaneous overcurrent relays react immediately when the current exceeds the set point, offering the fastest protection but typically used for high fault currents. Time-delayed overcurrent relays, on the other hand, introduce a delay before tripping, which can be fixed or inverse. Inverse time relays offer faster operation for higher fault currents and slower operation for lower fault currents, providing a balance between sensitivity and selectivity.

These relays are essential components in power system protection schemes. They work in conjunction with current transformers (CTs) which step down the high currents in the power system to a level that the relay can safely measure. The coordination of multiple overcurrent relays throughout a network is critical to ensure that only the faulty section is isolated, minimizing disruption to the rest of the system. They are widely used in industrial, commercial, and utility applications.