Combined overvoltage and undervoltage
relay REU 523
1MRS 751123-MBG
2
Application The over and undervoltage relay REU 523 is
a secondary relay which is connected to the
voltage transformers of the object to be pro-
tected. 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 applica-
tion 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 undervolt-
age 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 calcu-
lated 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 calcu-
lated 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 may be assigned either a def-
inite-time or an IDMT characteristic. When
the IDMT characteristic is chosen, two
time/voltage curve groups, A and B, are
available.
It is possible to block the start and the trip-
ping of an overvoltage stage by applying an
external binary input signal to the relay.
High-set stage U>> can be set out of opera-
tion. This state will be indicated by three
dashes “---” on the LCD and by “999” when
the set start current value is read via serial
communication.
Undervoltage unit
When the voltage values fall below the set
start value of low-set stage U<, the undervolt-
age unit will start to deliver a start signal after
a ~ 80 ms’ start time. When the set operate
time at definite-time characteristic or the cal-
culated operate time at IDMT characteristic
elapses, the undervoltage unit will deliver a
trip signal.
The high-set undervoltage stage can be set to
start and trip either based on conventional
undervoltage measurement or on the calcu-
lated positive-phase-sequence voltage, U1s.
Selecting either of these two will automati-
cally deseclect the other.
When the conventional protection mode is
selected for the high-set undervoltage stage
and the voltage values fall below the set start
value of high-set stage U<<, the undervoltage
unit will start to deliver a start signal after a
~50 ms’ start time.
When the positive-phase-sequence protec-
tion mode is selected for the high-set under-
voltage stage and the calculated positive-
phase-sequence voltage value, U1s, falls
below the set start value of high-set stage
U<<, the undervoltage 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 und-
ervoltage unit will deliver a trip signal.
The low-set and the high-set stage of the und-
ervoltage unit may be assigned either a defi-
nite-time or an IDMT characteristic. When
the IDMT characteristic is chosen, one
time/voltage curve group, C, is available.
