Systems & Electronics

UHR4N – Digital multifunction generator stator earth fault protection relay

The multifunction protection relay UHR4N belongs to SIGMA-N digital protection line and it performs functions as generator protection relay against stator earth faults in generator systems.

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


Stator earth fault 95% – residual overvoltage

64S – 95%

Stator earth fault 100%

64S – 100%


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 UHR4N relay manages the following thresholds:

  • 3 stator earth fault 100% thresholds (stator insulation resistance R1<, R2< and R<<)
  • 2 residual overvoltage thresholds – 95% stator earth fault (Uo>, Uo>> )

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.