Systems & Electronics

IDT8N – Digital percentage biased transformer differential protection relay

The multifunction protection relay IDT8N belongs to SIGMA-N digital protection line and it performs function as three-poles percentage biased differential protection relay for transformer or generator-transformer units.

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


Three-poles percentage biased differential protection for transformers


Three-poles overcurrent protection

50 – 51

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 – the IDT8N relay manages the following thresholds:

  • 1 differential percentage biased threshold (two branches)
  • 1 absolute value differential threshold
  • 2 overcurrent thresholds (one for each side of the protected transformer)

All the thresholds are definite time and 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