Application

The over and undervoltage relay REU 523 is a secondary relay which is connected to the

voltage transformers of the object to be protected. The over and the undervoltage unit

continuously measure the fundamental wave of the phase-to-phase voltages of the object.

On detection of a fault, the relay will start, trip the circuit breaker, provide alarms, record

fault data, etc., in accordance with the application and the configured relay functions.

The overvoltage unit includes low-set stage U> and high-set stage U>> and the undervolt

age unit low-set stage U< and high-set stage U<<. The high-set undervoltage stage can

alternatively be set to evaluate the positive phase-sequence voltage. In addition, the high

set undervoltage stage can be configured to evaluate only one instead of three phase-to

phase voltages.

The protection functions are independent of each other and have their own setting groups

and data recordings. The over and undervoltage functions use conventional voltage trans

former measurement.

An output contact matrix allows start or trip signals from the protection stages to be

routed to the desired output contact.

Design

The relay includes a high-set and low-set overvoltage unit, a high-set and low-set und

ervoltage unit and a circuit-breaker failure protection unit. Further, the relay includes an

HMI module, a self-supervision system and a disturbance recorder.