ABB REU 523 Product manual

REU 523
Combined Overvoltage and
Undervoltage Relay
Technical Reference Manual

3
Combined Overvoltage and
Undervoltage Relay
Technical Reference Manual
REU 523
1MRS 750942-MUM
Issued: 07.06.99
Version: B/05.07.2002
Checked: A.S.
Approved: L.N.
We reserve the right to change data without prior notice.
Contents
1. Introduction ...............................................................................5
1.1. About this manual .........................................................................5
1.2. The use of the relay ......................................................................5
1.3. Features ........................................................................................5
1.4. Guarantee .....................................................................................6
2. Safety information .....................................................................7
3. Instructions ................................................................................8
3.1. Application .....................................................................................8
3.2. Requirements ................................................................................8
3.3. Configuration .................................................................................8
4. Technical description .............................................................10
4.1. Functional description .................................................................10
4.1.1. Product functions .............................................................10
4.1.1.1. Schema of product functions ..............................10
4.1.1.2. Overvoltage, undervoltage and
positive-phase-sequence ...................................10
4.1.1.3. Inputs .................................................................11
4.1.1.4. Outputs ...............................................................11
4.1.1.5. Circuit-breaker failure protection unit .................11
4.1.1.6. Disturbance recorder ..........................................11
4.1.1.7. HMI module ........................................................11
4.1.1.8. Non-volatile memory ..........................................11
4.1.1.9. Self-supervision ..................................................12
4.1.2. Measurements .................................................................12
4.1.3. Configuration ....................................................................13
4.1.4. Protection .........................................................................14
4.1.4.1. Block diagram ....................................................14
4.1.4.2. Overvoltage unit .................................................14
4.1.4.3. Undervoltage unit ...............................................15
4.1.4.4. Positive-phase-sequence protection ..................16
4.1.4.5. Time/voltage characteristics ...............................17
4.1.4.6. Settings ..............................................................20
4.1.4.7. Technical data on protection functions ..............28
4.1.5. Indicator LEDs and alarm indication messages ...............29
4.1.6. Monitoring of demand values ...........................................30
4.1.7. Commissioning test ..........................................................30
4.1.8. Disturbance recorder .......................................................30

4
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
4.1.8.1. Function .............................................................30
4.1.8.2. Disturbance recorder data .................................30
4.1.8.3. Control and indication of disturbance recorder
status .................................................................31
4.1.8.4. Triggering ...........................................................32
4.1.8.5. Settings and unloading ......................................32
4.1.8.6. Event code of the disturbance recorder .............32
4.1.9. Recorded data of the last events .....................................32
4.1.10.External serial communication .........................................33
4.1.10.1.Communication ports .........................................33
4.1.10.2.IEC 60870-5-103 remote communication
protocol ..............................................................34
4.1.10.3.Event codes .......................................................37
4.1.10.4.SPA bus communication protocol parameters ...39
4.1.11.Self-supervision (IRF) system ..........................................46
4.1.12.Relay parameterization ....................................................46
4.2. Design description ......................................................................47
4.2.1. Input/output connections .................................................47
4.2.2. Serial communication connections ..................................49
4.2.3. Technical data ................................................................50
5. Ordering information ............................................................. 54
6. References .............................................................................. 55
7. Index ........................................................................................ 56
8. Abbreviations ......................................................................... 59
9. Check lists ......................................................................... 60
10.Customer feedback ............................................................... 63

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
5
1. Introduction
1.1. About this manual
The purpose of this manual is to provide the user with thorough information on the
protection relay REU 523 and its applications, focusing on giving a technical
description of the relay.
Refer to the Operator’s Manual for instructions on how to use the
Human-Machine Interface (HMI) of the relay, also known as the Man-Machine
Interface (MMI), and to the Installation Manual for installation of the relay.
1.2. The use of the relay
The voltage relay REU 523 is intended for over and undervoltage protection in
medium voltage distribution networks but can also be used for protection of
generators, motors and transformers.
The REU 523 is based on a microprocessor environment. A self-supervision system
continuously monitors the operation of the relay.
The HMI includes a Liquid Crystal Display (LCD) which makes the local use of the
relay safe and easy.
Localcontroloftherelayviaserialcommunicationcanbe carriedoutwithaportable
computer connected tothe frontconnector and remote control via the rearconnector
connected to the distribution automation system through the serial interface and the
fibre-optic bus.
1.3. Features
• Single or three-phase use
• High-set overvoltage stage with definite-time or inverse definite minimum time
(IDMT) characteristic
• Low-set overvoltage stage with definite-time or IDMT characteristic
• High-set undervoltage stage with definite-time or IDMT characteristic
• Low-set undervoltage stage with definite-time or IDMT characteristic
• Positive-phase-sequence protection
• Ajustable drop-off/pick-up ratio for the low-set stages
• Circuit-breaker failure protection (CBFP)
• Disturbance recorder
• recording time up to 12 seconds
• triggering by a start or a trip signal from a protection stage and/or by a binary
input signal
• records three analogue channels and eight digital channels
• adjustable sampling rate

6
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
• Non-volatile memory for
• up to 60 event codes
• setting values
• disturbance recorder data
• recorded data of the five last events with time stamp
• number of starts for each stage
• alarm indication messages and LEDs showing the status at the moment of
power failure
• Three accurate voltage inputs
• Galvanically isolated binary input with a wide input voltage range
• All settings can be modified with a personal computer
• HMI with an alphanumeric LCD and manoeuvring buttons
• IEC 60870-5-103 and SPA bus communication protocols
• Two normally open power output contacts
• Two change-over signal output contacts
• Output contact functions freely configurable for desired operation
• Optical PC-connector for two-way data communication (front)
• RS-485 connector (rear) for system communication
• Continuous self-supervision of electronics and software. At an internal relay
fault (IRF), all protection stages and outputs are blocked.
• User-selectable rated frequency 50/60 Hz
• User-selectable password protection for the HMI
• User-selectable nominal voltage 100/110/115/120 V
• Display of primary voltage values
• Demand values
• Multi-language support
1.4. Guarantee
Please inquire the guarantee of your nearest ABB representative.

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
7
2. Safety information
Dangerous voltages can occur on the connectors, even though the
auxiliary voltage has been disconnected
National and local electrical safety regulations must always be
followed
The device contains components which are sensitive to electrostatic
discharge
The frame of the device has to be carefully earthed
Only a competent electrician is allowed to carry out the electrical
installation
Non-observance can result in death, personal injury or substantial
property damage
Breaking the sealing tape on the rear panel of the device will result in
loss of warranty and proper operation will no longer be guaranteed
!

8
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
3. Instructions
3.1. 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 voltagesof the object. On detection ofa 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
undervoltage 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 transformer measurement.
An output contact matrix allows start or trip signals from the protection stages to be
routed to the desired output contact.
3.2. Requirements
When the REU 523 is operating under the conditions specified below (see also
Technical data), it will be practically maintenance-free. The relay includes no parts
or components subject to abnormal physical or electrical wear under normal
operating conditions.
Environmental conditions
3.3. Configuration
Setting and connection example
The appropriate configuration of the output contact matrix enables the use of the
signals from the overcurrent and the earth-fault unit as contact functions. The start
signals can be used for blocking co-operating protection relays, signalling and
initiating autoreclosing.
Figure 3.3.-1 represents the REU 523 with the default configuration.
• Specified ambient service temperature range -10...+55 °C
• Temperature influence on the operation accuracy of the
protection relay within the specified ambient service
temperature range
0.1% / °C
• Transport and storage temperature range -40...+70 °C

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
9
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100 V 110 V 115 V
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Blocking of stage U>>
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x = Factory Default
Optical
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Serial
port
I/O
INDICATIONS CLEARED
OUTP. CONT. UNLATCHED
AND INDIC. CLEARED
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MEMORIZED VALUES AND
INDIC. CLEARED; OUTPUT
CONTACTS UNLATCHED

10
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
4. Technical description
4.1. Functional description
4.1.1. Product functions
4.1.1.1. Schema of product functions
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4.1.1.2. Overvoltage, undervoltage and positive-phase-sequence
Refer to sections:
• 4.1.4.2.“Overvoltage unit”
• 4.1.4.3. “Undervoltage unit”
• 4.1.4.4. “Positive-phase-sequence protection”
59
U12
U23
U31
PrFU5_3
47
27
59
27
PO1
PO2
SO1
SO2
IRF
62 BF
D efinite- or inverse-time overvoltage
protection, low-set stage
Definite- or inverse-time undervoltage
protection, low-set stage
Definite- or inverse-time undervoltage
protection, high-set stage
Serial communication
Remote reset, remote setting control or blocking input
for the different protection stages
Circuit-breaker failure protection
Definite- or inverse-time positive-phase-
sequence protection stage
Definite- or inverse-time overvoltage
protection, high-set stage
Optical
pc-interface
Binary input BI

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
11
4.1.1.3. Inputs
The REU 523 includes three energizing inputs and one external binary input
controlled by an external voltage. For details, refer to section Input/output
connections and tables 4.1.4.6-6, 4.2.1-1 and 4.2.1-5. The function of the binary
input is determined with the SGB switches.
4.1.1.4. Outputs
The REU 523 is provided with two power outputs (PO1 and PO2) and two signal
outputs (SO1 and SO2). Switchgroups SGR1...8 are used for routing start and trip
signals from the protection stages to the desired signal or power output. PO1 and
PO2 can be configured to be latched and the minimum pulse length to 40 or 80 ms.
4.1.1.5. Circuit-breaker failure protection unit
The REU 523 features a circuit-breaker failure protection (CBFP) unit. The CBFP
unit will generate a trip signal via output PO2 if the fault has not been cleared on
expiration of the set operate time 0.10 s...1.00 s.
Normally, the CBFP unit controls the upstream circuit breaker. It can also be used
for tripping via redundant trip circuits of the same circuit breaker. The CBFP unit is
activated with a switch of switchgroup SGF1.
4.1.1.6. Disturbance recorder
The REU 523 includes an internal disturbance recorder which records the
momentary measured values, or the RMS curves of the measured signals, and eight
digital signals: the external binary input signal and the states of the internal
protection stages. The disturbance recorder can be set to be triggered by a start or a
trip signal from any protection stage and/or by an external binary input signal, and
either on the falling or rising triggering edge.
4.1.1.7. HMI module
The HMI of the REU 523 is equipped with six push-buttons and an alphanumeric
2x16 characters’ LCD. The push-buttons are used for navigating in the menu
structure and for adjusting set values.
An HMI password can be set to protect all user-changeable values from being
changed by an unauthorised person. The HMI password will remain inactive and
will thus not be required for altering parameter values until the default HMI
password has been replaced. Entering the HMI password successfully can be
selected to generate an event code. This feature can be used to indicate interaction
activities via the local HMI. For further information on the HMI, refer to the
Operator’s Manual.
4.1.1.8. Non-volatile memory
The REU 523 can be configured to store various data in the non-volatile memory,
which will retain its data also in case of loss of auxiliary voltage. Alarm indication
messagesandLEDs,thenumberofstarts,disturbancerecorderdata,eventcodesand
recorded data can all be configured to be stored in the non-volatile memory whereas
setting values will always be stored.

12
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
4.1.1.9. Self-supervision
The self-supervision system of the REU 523 manages run-time fault situations and
informs the user about an existing fault. When the self-supervision system detects a
permanent internal relay fault, the READY indicator LED will start to blink. At the
same time the self-supervision alarm relay (also referred to as the IRF relay), which
is normally picked up, will drop off and a fault code will appear on the LCD. The
fault code is numerical and identifies the fault type. For fault codes, refer to section
Internal fault in the Operator’s Manual.
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Fault codes can indicate:
• no response on the output contact test
• faulty program, work or parameter memory
• too high or too low a reference voltage value
4.1.2. Measurements
The table below presents the measured values which can be accessed through the
HMI, expressed as multiples of the rated voltage, Un, of the energizing input.
Faultc
C
E
STARTREADY TRIP
INTERNAL FAULT
FAULT CODE :56
Table 4.1.2-1 Measured values
Indicator Measured data
U12 Main voltage U12
U23 Main voltage U23
U31 Main voltage U31
U1s Positive-phase-sequence voltage
Umax Maximum voltage of the three main voltages
Umin Minimum voltage of the three main voltages
U1min Average voltage of the three main voltages during one minute
U10min Average voltage of the three main voltages during ten minutes

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
13
4.1.3. Configuration
The figure below illustrates how the start, trip and binary input signals can be
configured to obtain the required protection functionality.
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The functions of the blocking and start signals are selected with the switches of
switchgroups SGF, SGB and SGR. The checksums of the switchgroups are found
under“SETTINGS”inthe HMI menu.Thefunctionsoftheseswitchesareexplained
in detail in the corresponding SG_ -tables.
17 18
X2.1 13 14 15 10 11 12 7 8 9 3 45 6
SDiag_U5_3
3U>
3U>>
3U<
3U<<
4
5
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U23
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7
8
1
2
3
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
1
1
1
1
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1
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1
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START
TRIP
START
TRIP
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SGR6
SGR7
SGR8
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START
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TRIP
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SGB1
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Blocking of stage U<<
Blocking of stage U<
Blocking of stage U>>
Blocking of stage U>
INDICATIONS CLEARED
OUTP. CONT. UNLATCHED
AND INDICATIONS CLEARED
MEMORIZED VALUES AND
INDIC.CLEARED; OUTPUT
CONTACTS UNLATCHED
SWITCHGROUP SELECTION

14
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
4.1.4. Protection
4.1.4.1. Block diagram
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4.1.4.2. 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
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.
It is possible to block the tripping of an overvoltage 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.
SGR2/x
SGR1/x
1
1
SGR7/x
SGR8/x
SGR6/x
SGR5/x
U<<
t<<, k<<
U>
U>>
U<
U<<
t>
t>>
t<
t<<
60 ms
50 ms
SGF2/5
SGF2/2
SGB1/6
BI
SGB1/5
SGB1/8
SGR3/x
SGR4/x
U>>
t>>, k>>
50 ms
SGF2/6
SGF4/3...4
SGF2/7
t<, k<
SGB1/7
U
U
U
U>
t>, k>
SGF4/1...2
U<
80 ms
SGF4/5
C
SGF3/1, 3, 5,7
SGF3/2, 4, 6, 8
SGF2/4
&
&
U1s
BlockU5_3
C
0.20 Un
0.20 Un
SGF4/6
12
23
31
SGB1/4
SGB1/1
SGB1/2
SGB1/3
2
1
PO1
SGF1/1
40/80 ms
SGF1/5
PO2
5 s
1
0.1 ... 1s
SGF1/4
40/80 ms
C
SO1
3
SO2
4
SGF1/3
40/80 ms
40/80 ms
SGF1/2
1
5 s
C
1
SGF2/8
START
TRIP
CLEAR INDICATIONS AND MEMORIZED VALUES; UNLATCH
OUTPUT CONTACTS
CLEAR INDICATIONS AND UNLATCH OUTPUT CONTACTS
CLEAR INDICATIONS
SETTINGS (Group 1/Group 2)

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
15
4.1.4.3. Undervoltage unit
When the voltage values fall below the set start value of low-set stage U<, the
undervoltage 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 calculated operate time at
IDMT characteristic elapses, the undervoltage unit will deliver a trip signal.
The high-set undervoltage stage, U<<, can be set to start and trip either based on
conventional undervoltage measurement or on the calculated
positive-phase-sequence voltage, U1s. Selecting either of these two will
automatically deseclect the other.
Whentheconventionalprotectionmode has beenselectedandthevoltagevaluesfall
below the set start value of the high-set stage, the undervoltage unit will start to
deliver a start signal after a ~ 50 ms’ start time.
When the positive-phase-sequence protection mode has been selected and the
calculated positive-phase-sequencevoltagevalue,U1s,fallsbelow thesetstartvalue
of the high-set stage, 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 undervoltage unit will
deliver a trip signal.
The start and the tripping of an undervoltage stage can be set to be internally blocked
when the measured value falls below 0.2 x Unwith a switch of switchgroup SGF2.
In addition, the tripping of stage U< can be set to be blocked by the start of stage
U<<. The tripping of an undervoltage stage can also be blocked 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.

16
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
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4.1.4.4. Positive-phase-sequence protection
The high-set undervoltage stage can be set to be based on the calculated
positive-phase-sequence voltage in addition to on phase-to-phase voltage
measurement. The relay will then calculate the voltage based on the two
phase-to-phase voltages, U12 and U23.
The positive-phase-sequence protection function can be applied to disconnecting a
smaller power plant from the outside network, as when there is a fault in the network
which may prove critical for the power plant, e.g. a short circuit either at the
transmission or distribution network level.
A situation of this kind may be critical for different reasons. The power plant may
be left to feed an isolated network due to a trip caused by a fault. In this case, there
is a risk that the isolated network, in an asynchronous state compared to the rest of
the network, will be reconnected to the network, e.g. as a result of an autoreclosure.
In addition, the power plant may also fall into an asynchronous state in a fault
situation. These critical situations may be prevented by disconnecting the power
plant from the network fast enough by tripping the connecting circuit breaker.
The benefit of this function is that the voltage value measured during or after a
network fault is a good measure of how criticalthe fault is fora smaller power plant.
When the positive-phase-sequence voltage falls below the critical limit, the power
plant will have to be disconnected from the network.
The REU 523 measuring the positive-phase-sequence voltage complements other
methods used to disconnect smaller power plants. The application of these methods
is based on frequency and current measurement.
t
U/Un
t
t
U<<
Un
U<
Un
0.2 Un
x
U<
t<
U<<
t<<
t<
t<<
20PERC

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
17
The positive-phase-sequence protection function requires that the relay is in
three-phase and not in single-phase use.
4.1.4.5. Time/voltage characteristics
Each of the over and undervoltage stages can be given either a definite-time or an
inverse definite minimum time (IDMT) characteristic. The settings of switches
SGF4/1 and SGF4/2 determine the operation mode of stage U>, those of switches
SGF4/3 and SGF4/4 that of stage U>>, those of switch SGF4/5 that of stage U< and
those of switch SGF4/6 that of stage U<<. Refer to section Settings for further
information.
At IDMT characteristic, the operate time of the stage is dependent on the voltage
value: the greater the deviation from the setting value, the shorter the operate time.
Three time/voltage curve groups are available: A, B and C.
The recording of the operate time does not start until the deviation between the
measured voltage and the setting value exceeds six percent. The operate time
accuracy stated in the technical data applies when the deviation is ten percent or
higher.
Characteristics of the overvoltage stages
The IDMT characteristic curve groups A and B are designed for overvoltage stages
U> and U>>. Stages U> and U>> can be configured to use different characteristics.
The relationship between time and voltage at IDMT characteristic can be expressed
as follows:
where
t = operate time
k = time multiplier k> or k>>
U = measured voltage
U> = set start value for U> or U>>
a = constant 480
b = constant 32
c = constant 0.035
p = constant (see table 4.1.4.5-1)
The A- and B-type characteristics are illustrated in Fig. 4.1.4.5.-1 and Fig. 4.1.4.5.-2.
ts[] ka×
bUU>–
U>
------------------ 0.5–×

 p
-------------------------------------------------- c+=

18
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
Characteristic of the undervoltage stages
The IDMT characteristic curve group C is designed for undervoltage stages U< and
U<<. Stages U< and U<< can be configured to use different characteristics. The
relationship between time and voltage at IDMT characteristic can be expressed as
follows:
where
t = operate time
k = time multiplier k< or k<<
U = measured voltage
U< = set start value for U< or U<<
a = constant 480
b = constant 32
c = constant 0.055
p = constant (see table 4.1.4.5-1)
The C-type characteristic is illustrated in Fig. 4.1.4.5.-3.
Table 4.1.4.5-1 Values of constant p
Time/voltage
characteristic ABC
p232
ts[] ka×
bU<U–
U<
------------------ 0.5–×

 p
-------------------------------------------------- c+=

1MRS 750942-MUM Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
19
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1000
100
10
1
0,1
0,01
1,1 1,2 1,3 1,4 1,5 U/U>, U/U>>
0,05
0,2
0,4
0,7
1,0
k>, k>>
t/s
1,0
2,0
1,4
ovolt_Aext
0,05
0,2
0,4
0,7
1,0
k>, k>>
U/U>, U/U>>1,51,41,31,2
1
10
100
1000
t/s
1,11,0
0,01
0,1
2,0
1,4
ovolt_Bext

20
1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
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4.1.4.6. Settings
There are two alternative setting groups available, setting groups 1 and 2. Either of
these setting groups can be used as the actual settings, one at a time. Both groups
have their related registers. By switching between the setting groups a whole group
of settings can be changed at the same time. This can be done in any of the following
ways:
Group configuration:
• via the HMI
• entering parameter V150 via serial communication
Group selection:
• switching between Group1 and Group2 is accomplished by means of the external
binary input
The setting values can be altered via the HMI or with a personal computer provided
with the Relay Setting Tool. Before the relay is connected to a system it must be
assured that the relay has been given the correct settings. If there is any doubt, the
setting values should be read with the relay trip circuits disconnected or tested with
voltage injection; refer to section Check lists for additional information.
1,0
0,7
0,4
k<, k<<
0,2
0,1
U/U<,
U/U<< 0,5 0,6 0,7 0,8 0,9 1,0
0,01
0,1
1
10
100
1000
uvolt_Cext
1,4
2,0