The REU 523 is intended for overvoltage and undervoltage protection in medium

voltage distribution networks but can also be used for protection of generators,

motors and transformers.

The REU 523 continuously evaluates the fundamental wave of the three phase-to

phase voltages. In addition, the high-set undervoltage stage can be configured to

evaluate either only one instead of three phase-to-phase voltages or the

positive-phase-sequence voltage.

The REU 523 is based on a microprocessor environment. A self-supervision system

continuously monitors the operation of the electronics and the software.

The HMI includes a Liquid Crystal Display (LCD) which makes the local use of the

relay safe and easy.

Local control of the relay can be carried out using a portable computer connected to

the front connector and remote control via the rear connector connected to the

distribution automation system through the serial interface and the fibre-optic bus.