Systems & Electronics

IFD4L – Digital multifunction protection relay for M.V. lines

The multifunction protection relay IFD4L belongs to SIGMA-L digital protection line and it performs functions as phase overcurrent, earth fault (directional and not directional) and residual overvoltage relay.

IFD4L relay is compliant with Italian document Norma CEI 0-16 in reference to “general protections” and is equipped with internal Logger.

The user can select the insertion mode, the protection functions and auxiliary functions in compliance to the table below:



Two-phases overcurrent

50 51

Two-phases overcurrent + lo

50 51 50N 51N

Two-phases overcurrent + Uo

50 51 59N

Two-phases overcurrent + lo + Uo

50 51 50N 51N 67N 59N

Earth-fault overcurrent (non direct.) lo

50N 51N

Residual overvoltage (Uo)

Earth-fault (lo + Uo) 50N 51N 67N 59N

2nd harmonic restraint


Cold Load Pickup

Breaker failure
Circuit breaker monitoring


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 – IFD4L manages the following thresholds:

  • 3 phase overcurrent thresholds
  • 3 earth fault overcurrent thresholds
  • 3 directional earth fault thresholds
  • 2 residual overvoltage thresholds

The first threshold of each protection function can be programmed either definite time or dependent time in compliance with IEC 60255-151 specifications; other thresholds are definite time only. Each definite time threshold delay can be combined with an additional delay controlled by the digital inputs.

The trip of a threshold is shown by LEDs and with a specific message on the display.