Systems & Electronics

IFD4N – Digital multifunction protection relay for MV lines

The multifunction protection relay IFD4N belongs to SIGMA-N digital protection line and it performs functions as 2phase overcurrent and directional earth fault relay for MV lines. IFD4N relay is compliant to the CEI 0-16 norm.

The user can select one or more of the functions listed in the table below:





Short circuit 50
Directional earth fault 67N
Overcurrent earth fault 51N
CB pole wearing index (121)  


All the functions of the relay are fully programmable by front panel keyboard or through a RS485 serial interface

using a personal computer with set-up program; furthermore the relay can be programmed through a

remote control and monitoring system.

Thresholds – IFD4N manages the following thresholds:

  • 3 phase overcurrent
  • 3 directional earth fault
  • 3 overcurrent earth fault

All thresholds are definite time, and for the first phase overcurrent and the first directional earth fault inverse time characteristic is available; each of them 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.

The directional earth fault function is used in electrical systems with:

  • unearthed neutral
  • neutral solidly earthed
  • neutral earthed through a resistor
  • via earthing transformer
  • neutral earthed through Petersen coil