Systems & Electronics

UAR4N – Digital under- and overvoltage multifunction relay

The protection relay UAR4N belongs to the SIGMA-N digital protection line and it performs functions as under- and overvoltage and residual overvoltage relay. The user can select any of the functions listed in the table below.

Undervoltage (2 or 3-phase) 27
Overvoltage (2 or 3-phase) 59
Under- and overvoltage (2 or 3-phase) 27 – 59
Residual overvoltage (Vo) 59 N – 59 Vo
Stator earth fault 95% (residual voltage) 64 S

Under- and overvoltage (2 or 3-phase)
+ residual overvoltage No)

27 – 59 – 59N

Under- and overvoltage (2 or 3-phase)
+ stator earth fault 95%

27 – 59 – MS
Voltage balance 60

All the functions of the relay are fully programmable either by front panel keyboard or through an 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 UAR4N relay manages up to 6 voltage thresholds as:

  • 2 undervoltage thresholds
  • 2 overvoltage thresholds
  • 2 residual overvoltage thresholds

The first thresholds of phase and residual voltage (U<, U> and Uo>) can be programmed either definite time or time dependent in compliance with BS-142 and IEC 255-4 specifications; the other thresholds are definite time only.

Each definite time threshold delay 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.