Systems & Electronics

IFX4N – IFX4NR Digital overcurrent and earth fault multifunction relay

The protection relay IFX4N – IFX4NR belongs to the SIGMAN digital protection line and it performs functions such as overcurrent and earth-fault relay. The user can select any of the functions listed in the table below.

Two-phase overcurrent 50 51

Three-phase overcurrent

50 51

Two-phase overcurrent + earth-fault

50 51 51N
Three-phase overcurrent + earth-fault 50 51 51N
Earth-fault overcurrent (non directional) 51N
Stator earth-fault (95%)


Transformer case earth-fault


IFX4NR type only 79
50 BF
Auto-reclosing function
Circuit-breaker failure
Circuit-breaker poles wearing index

All the functions of the relay are fully programmable either by front panel keyboard or through an RS485 serial interface by using a personal computer with set-up program; furthermore the relay can be programmed through a remote control and monitoring system.

Thresholds – the IFX4N relay manages up to 6 overcurrent thresholds as indicated below:

  • 3 phase overcurrent thresholds
  • 3 earth-fault overcurrent thresholds

The first threshold of phase overcurrent and of earth-fault (I> and Io>) can be programmed either definite time or time dependent in compliance with BS-142 and IEC 255-4 specifications; the other thresholds are definite time only.

Each definite time threshold delay can be combined with an additional timer controlled by the digital inputs.

The trip of the relay is shown by LEDs and by a message on the display.