ABB The over and undervoltage relay REU 523 is a secondary relay

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.

Overvoltage unit

When the voltage values exceed the set start value of low-set stage U>,  the overvoltage

unit will start to deliver a start signal after a ~60 ms’ start time. When the set operate time

at definite-time characteristic or the calculated operate time at inverse definite mini

mum time (IDMT) characteristic elapses, the overvoltage unit will deliver a trip signal.

When the voltage values exceed the set start value of high-set stage U>>, the overvoltage

unit will start to deliver a start signal after a ~50 ms’ start time. When the set operate time

at definite-time characteristic or the calculated operate time at IDMT characteristic

elapses, the overvoltage unit will deliver a trip signal.

The low-set and the high-set stage of the overvoltage unit can be given either a defi

nite-time or an IDMT characteristic. At IDMT characteristic, two time/voltage curve

groups, A and B, are available.

It is possible to block the tripping of an over voltage stage by applying an external binary

input signal to the relay.

The high-set stage can be set out of operation. This state will be indicated by dashes on the

LCD and by “999” when the set start value is read via serial communication.