Overcurrent relay REJ 523

Basic protection of busbars and feeders in utility substations and industrial power distribution systems

Not active product since 2011

The overcurrent relay REJ 523 is a secondary relay which is connected to the current transformers of the object to be protected. The overcurrent unit continuously measures the phase currents 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 overcurrent unit includes low-set stage I> and high-set stage I>>. If the high-set stage is given a setting 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 overcurrent 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.


  • Overcurrent protection relay iused as a secondary relay which is connected to the current transformers of the object to be protected

Product benfits

  • Flexible tripping and signalling facilities

Product features

  • Three-phase low-set overcurrent stage with definite time or inverse definite minimum time (IDMT) characteristic
  • Three-phase high-set overcurrent stage with instantaneous or definite time characteristic
  • Circuit-breaker failure protection unit (CBFP)
  • Disturbance recorder
  • HMI with an alphanumeric LCD and manoeuvring buttons
  • Continuous self-supervision

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