The earth-fault relay REJ 521 is a secondary relay which is connected to the current transformers of the object to be protected. The earth-fault unit continuously measures the neutral current of the object. On detection of a fault, the relay will start, trip the circuit breaker, provide alarms, record fault data, etc., in accordance with the application and the configured relay functions.
The earth-fault unit includes low-set stage I0 > and high-set stage I0 >>. If the high-set stage is given a setting value within the lower part of the setting range, the relay module will have two nearly identical stages. In this case, the relay can be used in two-stage load shedding applications.
The protection functions are independent of each other and have their own setting groups and data recordings. The earth-fault protection function uses conventional current transformer measurement.
An output contact matrix allows start or trip signals from the protection stages to be routed to the desired output contact.