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REA 421D1 Multifunction voltage protection

REA 421D1 is a multifunction voltage & frequency protection relay intended mainly for the HV and MV side of the Distribution substations, Generators, Motors, Distribution Generation objects (Solar, Wind parks) etc. It can be applied also in the EHV substations, where voltage & frequency control and protection is necessary.

For the MV side of the Distribution substations the protection can be used for load shedding during the deficit of the active power.

Through the measuring of voltage, angle and frequency difference the device is suitable for synchro-check control between two points of the network. 




All relay protection functions meet ANSI and IEC standards’ requirements:

  • Three stages definite time over voltage protection
  • Three stages definite time under voltage protection
  • Two stages negative sequence over voltage protection
  • Two stages positive sequence under voltage protection
  • Three stages neutral voltage displacement
  • Four stages definite time over frequency protection
  • Four stages definite time under frequency protection
  • Four stages definite time rate of change of frequency protection
  • Voltage vector shift protection
  • Fuse failure monitoring
  • Voltage circuits supervision
  • Clockwise and anticlockwise phase rotation function
  • Synchrocheck

Disturbance (Fault) Recorder

  • Sampling rate – 1 kHz/4kHz
  • User defined trigger conditions and records duration
  • Recording mode -overwrite (ring buffer) or saturate
  • Each sample consists of instantaneous values of all analog and digital values

Event Recorder

  • Up to 1000 records
  • Each event consists of information about the event’s type, some additional data (such as pick-up current, voltage, the time elapsed and so on) and the time stamp of the event (year, month, day, hour, minute, second, millisecond)
  • Recording mode - overwrite


  • Configuration tool - ROCON MMI protocol
  • SCADA communication - IEC 60870-5-103, MODBUS

Configuration, setting and administration


  • Optional extension with communication board with 2xFO redundant ethernet ports for IEC61850
  • Optional extension with I/O modules type of RTB-1


Note: All flyers are subject to regular update