Systems & Electronics

PQR4N – Digital multifunction generator protection relay

The multifunction protection relay PQR4N belongs to SIGMA-N digital protection line and it performs functions as generator protection relay against loss of excitation (or underexcitation conditions), antimotoring (reverse power) and against rotor earth faults. The user can select one or more of the functions listed in the table below:

Loss of excitation


Antimotoring (reverse power)


Rotor earth fault MR

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 PQR4N relay manages the following thresholds:

  • 2 loss of excitation (underexcitation) thresholds
  • 2 active power thresholds (max. or minimum)
  • 2 reactive power thresholds (max. or minimum)
  • 2 rotor insulation resistance thresholds

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.