Seg HighTECH MRU3-2 User manual

MRU3-2
PROTECTION TECHNOLOGY
MADE SIMPLE
VOLTAGE RELAY WITH EVALUATION OF
SYMMETRICAL COMPONENTS
HighTECH Line
VOLTAGE RELAY WITH EVALUATION OF SYMMETRICAL COMPONENTS
Revision: B
Original document
English
MANUAL

SEG Electronics GmbH Manual MRU3-2
2 DOK-TD-MRU3-2, Rev. B
SEG Electronics reserves the right to update any portion of this publication at any time.
Information provided by SEG Electronics is believed to be correct and reliable.
However, no responsibility is assumed by SEG Electronics unless otherwise expressly undertaken.
© SEG Electronics 1994–2020. All rights reserved.

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 3
Contents
1. Introduction and application.......................................................................5
2. Features and characteristics ......................................................................5
3. Design...........................................................................................................6
3.1 Connections ........................................................................................................................6
3.1.1 Analog input circuits........................................................................................................7
3.1.2 Blocking input..................................................................................................................7
3.1.3 External reset input .........................................................................................................7
3.1.4 Output relays...................................................................................................................7
3.1.5 Fault recorder..................................................................................................................8
3.1.6 Parameter settings..........................................................................................................9
3.2 Display...............................................................................................................................10
3.3 LEDs..................................................................................................................................10
3.4 Front plate.........................................................................................................................11
4. Working principle.......................................................................................12
4.1 Analog circuits...................................................................................................................12
4.2 Digital circuits....................................................................................................................12
4.3 Selection of star or delta connection.................................................................................13
4.4 Voltage supervision...........................................................................................................14
4.4.1 1-phase/3-phase supervision........................................................................................14
4.4.2 Principle of the voltage unbalance protection ...............................................................14
4.4.3 Measuring principle.......................................................................................................15
4.4.4 Negative sequence system of a symmetrical voltage system ......................................16
4.4.5 System with voltage unbalance.....................................................................................16
4.4.6 Zero sequence system..................................................................................................17
5. Operations and settings............................................................................18
5.1 Display...............................................................................................................................18
5.2 Setting procedure..............................................................................................................19
5.3 System parameter.............................................................................................................20
5.3.1 Display of residual voltage UE as primary quantity (Uprim/Usec).....................................20
5.3.2 D/Y –Switch - over........................................................................................................20
5.3.3 Setting of nominal voltage.............................................................................................20
5.3.4 Display of the activation storage...................................................................................21
5.3.5 Parameter set change-over switch/external trigger for fault recorder...........................21
5.4 Protection parameters.......................................................................................................22
5.4.1 1-phase or 3-phase U</U>-tripping...............................................................................22
5.4.2 Parameter setting of over- and under voltage supervision ...........................................22
5.4.3 Positive sequence system voltage (U1<, U1>).............................................................22
5.4.4 Negative sequence system overvoltage (U2>).............................................................22
5.4.5 Zero sequence system overvoltage (U0>)....................................................................22
5.4.6 Adjustment of the slave address...................................................................................22
5.4.7 Setting of Baud-rate (applies for Modbus-Protocol only)..............................................23
5.4.8 Setting of parity (applies for Modbus-Protocol only).....................................................23
5.5 Parameter for the fault recorder........................................................................................23
5.5.1 Adjustment of the fault recorder....................................................................................23
5.5.2 Number of the fault recordings......................................................................................23
5.5.3 Adjustment of trigger occurrences ................................................................................23
5.5.4 Pre-trigger time (Tvor)...................................................................................................23
5.6 Date and time....................................................................................................................24
5.6.1 Adjustment of the clock.................................................................................................24
5.7 Indication of measuring values..........................................................................................25
5.7.1 Measuring indication .....................................................................................................25
5.7.2 Unit of the measuring values displayed ........................................................................25
5.7.3 Indication in faultless condition .....................................................................................25
5.7.4 Indication after pickup / tripping ....................................................................................25
5.7.5 Indication of the phase sequence .................................................................................26
5.8 Fault memory ....................................................................................................................26
5.9 Additional Funktion............................................................................................................27

SEG Electronics GmbH Manual MRU3-2
4 DOK-TD-MRU3-2, Rev. B
5.9.1Setting procedure for blocking the protection functions ...............................................27
5.9.2 Reset.............................................................................................................................28
5.9.3 Erasure of fault storage ................................................................................................29
6. Relay testing and commissioning............................................................30
6.1 Power-On..........................................................................................................................30
6.2 Testing the output relays ..................................................................................................30
6.3 Checking the set values....................................................................................................31
6.4 Secondary injection test....................................................................................................32
6.4.1 Test equipment.............................................................................................................32
6.4.2 Example of the test circuit.............................................................................................32
6.4.3 Checking the input circuits and measuring functions ...................................................33
6.4.4 Test of the symmetrical components values ................................................................34
6.4.5 Checking the operating and resetting values of the over/under voltage functions.......36
6.4.6 Checking the relay operating time of the over/under voltage functions .......................36
6.4.7 Checking the external blocking and reset functions.....................................................36
6.5 Primary test.......................................................................................................................37
6.6 Maintenance .....................................................................................................................37
7. Technical Data............................................................................................38
7.1 Measuring input circuits....................................................................................................38
7.2 Common data ...................................................................................................................38
7.3 Setting ranges and steps..................................................................................................39
7.3.1 Interface parameter ......................................................................................................39
7.3.2 Parameter for the fault recorder....................................................................................40
7.4 Output relays ....................................................................................................................40
8. Order form..................................................................................................41

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 5
1.Introduction and application
The MRU3-2 is a relay for voltage supervision with universal application, it protects the three-phase
network against voltage unbalance or earth faults in isolated networks. Beside the pure rms value
measurement of the line voltage the MRU3-2 evaluates the symmetrical components (positive-,
negative- and zero sequence system). By evaluating these components relay MRU3-2 can detect
the phase sequence, voltage unbalance and earth-faults.
Important:
For additional common data of all MR-relays please refer to technical description "MR - Digital Mul-
tifunctional Relays".
2.Features and characteristics
Microprocessor technology with watchdog,
digital filtering of the measured values by using discrete Fourier analysis to suppress
higher harmonics and d.c. components induced by faults or system operations,
analog low pass filter,
two parameter sets,
voltage supervision each with two step under-/ and overvoltage detection,
voltage supervision for each phase separately
completely independent time settings for voltage supervision
separate tripping elements for over- and under-voltage and positive sequence system
overvoltage detection in negative- and zero sequence system,
display of measuring values of the line voltages and system voltages U0, U1 and U2 as
rms values (zero , positive- and negative sequence system)
alternatively connection and measurement of the phase-to-neutral or phase-to-phase
voltage
display of the phase sequence,
display of all measuring values and setting parameters for normal operation as well as
tripping via a alphanumerical display and LEDs,
display of measuring values as primary quantities,
tripping memory for all line voltages and the voltages of the symmetrical components,
storage and display of tripping values in a fault memory (voltage-failure safe),
recording of up to eight fault occurrences with time stamp
for blocking the individual functions by the external blocking input, parameters can be set
according to requirement,
suppression of indication after an activation (LED flash),
free assignment for output relays,
display of date and time,
in compliance with VDE 0435, part 303 and IEC 255,
mains frequency is adjustable to 50 Hz or 60 Hz or variable from 40 - 70 Hz,
RS485 interface for communication with master systems
serial data exchange via RS485 interface possible; alternatively with RS485
ProOpen Data Protocol or Modbus Protocol.

SEG Electronics GmbH Manual MRU3-2
6 DOK-TD-MRU3-2, Rev. B
3.Design
3.1 Connections
Figure 3.1: Star connection of the voltage transformers
Figure 3.2: Delta connection of the voltage transformers
Attention!
If the input transformers are connected in delta circuit no detection of zero phase sequence (U0) is
possible.

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 7
3.1.1 Analog input circuits
The analog input voltages are galvanic ally decoupled by the input transformers of the device, then
filtered and finally fed to the analog digital converter. Depending upon the demands the MRU3-2
can be connected directly to the mains or via external voltage transformers in star- or delta connec-
tion. The priority should be given to the star connection, because of the ability to detect a zero se-
quence system.
3.1.2 Blocking input
When the voltage, which must be in the admissible range of the auxiliary voltage, is connected to
terminals D8/E8, the following tripping functions are blocked undelayed:
Under voltage U</U<<
Over voltage U>/U>>
positive sequence system undervoltage U1<
positive sequence system overvoltage U1>
negative sequence system overvoltage U2>
zero sequence system overvoltage U0>
Blocking can be freely selected via the allocation mode. (refer to chapter 5.9).
Input D8 is the ground (L- or N) for blocking and the external reset. The blocked functions are again
released undelayed when the auxiliary voltage is disconnected from the terminals D8/E8.
The above mentioned functions remain blocked for 2 s after the supply voltage had been applied.
3.1.3 External reset input
Refer to chapter 5.9.2
3.1.4 Output relays
The MRU3-2 is equipped with 5 output relays.
Relay 1; C1, D1, E1 and C2, D2, E2
Relay 2; C3, D3, E3 and C4, D4, E4
Relay 3; C5, D5, E5
Relay 4; C6, D6, E6
Relay 5; Signal self-supervision (internal failure of the unit ) C7, D7, E7
All trip and alarm relays are working current relays, the relay for self supervision is an idle current
relay.

SEG Electronics GmbH Manual MRU3-2
8 DOK-TD-MRU3-2, Rev. B
3.1.5 Fault recorder
The MRU3-2 has a fault value recorder which re-cords the measured analog values as instantane-
ous values.
The instantaneous values
UL1; UL2; UL3 for star connection orU12; U23; U31 for delta connection are
scanned at a raster of 1.25 ms (at 50 Hz) and 1.041 ms (at 60 Hz) and saved in a
cyclic buffer.
Storage division
Independent of the recording time, the entire storage capacity can be divided into several cases of
disturbance with a shorter recording time each. In addition, the deletion behavior of the fault
recorder can be influenced.
No writing over
If 2, 4 or 8 recordings are chosen, the complete memory is divided into the relevant number of
partial segments. If this max. number of fault event has been exceeded, the fault recorder block
any further recordings in order to prevent that the stored data are written over. After the data have
been read and deleted, the recorder to ready again for further action.
Writing over
If 1, 3 or 7 recordings are chosen, the relevant number of partial segments is reserved in the com-
plete memory. If the memory is full, a new recording will always write over the oldest one.
The memory part of the fault recorder is designed as circulating storage. In this example 7 fault re-
cords can be stored (written over).
Memory space 6 to 4 is occupied.
Memory space 5 is currently being written in
Figure 3.3: Division of the memory into 8 segments, for example

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 9
Since memory spaces 6, 7 and 8 are occupied, this example shows that the memory has been as-
signed more than eight recordings. This means that No. 6 is the oldest fault recording and No. 4
the most recent one.
Figure 3.4: Basic set-up of the fault recorder
Each memory segment has a specified storage time which permits setting of a time prior to the
trigger event.
3.1.6 Parameter settings
System parameters
Uprim/Usek Primary/secondary measured value display of the voltage tranfor
mers
D/Y Selection of switching groups
fNRated frequency
LED-Flash Suppression of LED flashing after activation
P2/FR Parameter switch/external trigger for the fault recorder
Protection parameters
1/3 1-phase or 3-phase U</U> tripping
U< Pickup value for under voltage
tU< Trip value for under voltage low set element
U<< Pickup value for under voltage
tU<< Trip value for under voltage high set element
U> Pickup value for overvoltage
tU> Trip value for overvoltage low set element
U>> Pickup value for overvoltage
tU>> Trip value for overvoltage high set element
U1< Pick-up value for under voltage in positive-phase sequence system
tU1< Trip value for under voltage in positive phase sequence system
U1> Pick-up value for overvoltage in positive phase sequence system
tU1> Trip value for overvoltage in positive phase sequence system
U2> Pick-up value for overvoltage in negative phase sequence system
tU2> Trip value for overvoltage in negative phase sequence system
U0> Pick-up value for overvoltage in zero phase sequence system
tU0> Trip value for overvoltage in zero-phase sequence system

SEG Electronics GmbH Manual MRU3-2
10 DOK-TD-MRU3-2, Rev. B
Parameters for the fault recorder
FR Number of disturbance events
FR Trigger events
FR Pre-trigger time Tvor
Date and time
Year Y = 00
Month M = 04
Day D = 18
Hour h = 07
Minute m = 59
Second s = 23
Additional functions
Blocking function
Relay configuration
Fault memory
3.2 Display
The display is used for indicating all setting- and measuring values. The actual measuring values
as also the fault values can be indicated. In faultless operation the indicated value of the normal
operation can be called by pressing the <SELECT> and <ENTER> pushbuttons.
After tripping the display changes into the tripping mode from where fault data can be called.
3.3 LEDs
LEDs L1, L2, L3, U1 and U2 left from the display are two-colored and indicate the measured quan-
tities; green for measuring values and red for fault indication.
LED U0 lights yellow which normally indicates (relay not tripped) that the measuring value of the
zero sequence system and in case of tripping the tripping value of the zero sequence system is
shown in the display.
The LED marked with the letters RS lights up during setting of the slave address for the serial inter-
face (RS 485) of the unit.
The LED marked with "FR" lights up during parameter setting at the fault recorder. When LED •
lights up, date and time are displayed. LED "PS" indicates the phase sequence.
The 9 LEDs below the <SELECT/RESET> pushbutton signalize the parameter of the individual
tripping elements. In case of tripping they indicate, together with the upper LEDs, the respective
kind of fault.
A permanent red light indicates tripping. When the tripping delay has not elapsed the LEDs of the
corresponding combination (at pickup) are flashing.
If one of the limit values is exceeded for only a short time before the set tripping delay is not ex-
pired, the corresponding LED combination flashes. This flashing is shorter than for warning. This
pickup warning signal can be switched off with a reset. This activation signal can be shut-down with
the "Reset" key (refer to chapter 5.9.2) or suppressed by the FLASH/NO_FLASH function. The ac-
tive parameter set is indicated by LED "P2". LED D/Y lights up during parameter setting for the in-
terlinking of the input voltage CTs.

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 11
3.4 Front plate
Figure 3.5: Front plate MRU3-2

SEG Electronics GmbH Manual MRU3-2
12 DOK-TD-MRU3-2, Rev. B
4.Working principle
4.1 Analog circuits
The input voltages are galvanic ally insulated by the input transformers. The noise signals caused
by inductive and capacitive coupling are suppressed by an analog R-C filter circuit.
The analog voltage signals are fed to the A/D-converter of the microprocessor and transformed to
digital signals through Sample- and Hold- circuits. The analog signals are sampled with a sampling
frequency of 16 x fN, namely, a sampling rate of 1.25 ms for every measuring quantity, at 50 Hz.
4.2 Digital circuits
The essential part of the MRU3-2 relay is a powerful microcontroller. All of the operations, from the
analog digital conversion to the relay trip decision, are carried out by the microcontroller digitally.
The relay program is located in an EPROM (Electrically-Programmable-Read-Only-Memory). With
this program the CPU of the microcontroller calculates the three phase voltage in order to detect a
possible fault situation in the protected object.
For the calculation of the voltage value an efficient digital filter based on the Fourier Transformation
(DFFT - Discrete Fast Fourier Transformation) is applied to suppress high frequency harmonics
and d.c. components caused by fault-induced transients or other system disturbances. The micro-
processor continuously compares the measured values with the preset thresholds stored in the
parameter memory (EEPROM). If a fault occurs an alarm is given and after the set tripping delay
has elapsed, the corresponding trip relay is activated.
The relay setting values for all parameters are stored in a parameter memory (EEPROM - Electri-
cally Erasable Programmable Read Only Memory), so that the actual relay settings cannot be lost,
even if the power supply is interrupted.
The microprocessor is supervised by a built-in "watchdog" timer. In case of a failure the watchdog
timer resets the microprocessor and gives an alarm signal via the output relay "self supervision".

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 13
4.3 Selection of star or delta connection
All six connections of the input voltage transformers are led to screw terminals. The nominal volt-
age of the device is equal to the nominal voltage of the input transformers. Dependent on the appli-
cation the input transformers can be connected in either delta or star. The connection for the
phase-to-phase voltage is the delta connection. In star connection the measuring voltage is re-
duced by 1/ √3. During parameter setting the connection configuration either Y or has to be ad-
justed.
Figure 4.1: Input v.t.s in delta connection (D)
Figure 4.2: Input v.t.s in star connection (Y)

SEG Electronics GmbH Manual MRU3-2
14 DOK-TD-MRU3-2, Rev. B
4.4 Voltage supervision
4.4.1 1-phase/3-phase supervision
The voltage relay MRU3-2 protects electrical generation systems, consumers and appliances in
general against over- and/or under voltage. The re-lay is equipped with an independent, 2-step
over- (U>, U>>) and under voltage supervision (U<, U<<) with separately adjustable tripping values
and de-lay times. Voltage measuring is 3-phase. In this process there is a continuous comparison
of the line conductor voltages in case of a delta connection and of the phase voltages in case of a
star connection with the preset limit values.
With the MRU3-2 the highest voltage is always evaluated for overvoltage supervision and the
lowest voltage for under voltage supervision.
A distinction is made between 1-phase and 3-phase tripping. (1/3 –Parameter)
With 1-phase tripping the voltages are evaluated as follows:
U</U<</U</U>>: Activation cum tripping takes place if at least one phase has fallen short of the
tripping value.
With 3-phase tripping the voltages are evaluated as follows:
U<: Activation cum tripping takes place if all three phases have fallen short of the tripping value.
U<<: Activation cum tripping takes place if one phase has fallen short of the tripping value.
U>: Activation cum tripping takes place if all three phases have exceeded the tripping value.
U>> Activation cum tripping takes place if one phase has exceeded the tripping value.
4.4.2 Principle of the voltage unbalance protection
The principle of this procedure is to detect faults which affect an asymmetry of the voltage vector.
A single-phase line interruption can for instance cause voltage unbalance in the mains which does
not guarantee that the voltage will be zero in the faulty phase. Especially in higher impedance net-
works the missing phase can partly be rebuilt through running engines or transformers. A pure un-
dervoltage protection cannot detect this condition, however, the rebuilt phase does not coincide
with its old position in amount and phase. So an asymmetrical voltage vector system is formed.
In a compensated or isolated grid a single-phase earth fault will hardly cause a significant earth
current. Because, however, the faulty phase takes on the earth potential the entire voltage vector
system is shifted by the amount of the faulty phase and does not rotate anymore around the initial
star point (earth). The relative position of the voltage vectors between each other is hereby not
changed. Also this vector system is not symmetrical anymore in relation to the earth potential.
The MRU3-2 can detect such asymmetry.

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 15
4.4.3 Measuring principle
Any rotating three-phase system (original system) can be replaced by three symmetrical systems
acc. to the method of the "symmetrical components", a positive sequence system, a negative se-
quence system and a zero sequence system.
Positive sequence system U1:
The rms value of the positive sequence system represents the component of the original system
which is symmetrical and rotates in the positive direction acc. to its definition. A pure symmetrical
voltage vector system consists only of its positive sequence system.
The residual voltage in the positive sequence system is calculated by:
U1 = 1/3 | ( U1+ a1U2+ a2U3) |
Negative sequence system U2:
The rms value of the negative sequence system describes the component of the vector system
which rotates in negative direction. The rotating field, which rotates in the mathematical sense in
the negative direction (so-called "left rotating field"), consists only of a negative sequence sys-tem.
A measure for the size of the asymmetry of the original system represents the residual voltage in
the negative sequence system.
The residual voltage in the negative sequence sys-tem is calculated as follows:
U2 = 1/3 | ( U1 + a2 U2 + a1 U3) |
Zero sequence system U0:
The zero sequence system describes the displacement of the vector star point from the refer-ence
star point. This reference star point is generally the earth potential.
The residual voltage in the zero sequence system is calculated as:
U0 = 1/3 | ( U1+ U2+ U3) |
Used variables:
(complex vectors are underlined)
U1 rms value vector of phase voltage L1
U2 rms value vector of phase voltage L2
U3 rms value vector of phase voltage L3
U0 rms value of the zero sequence system
U1 rms value of the negative sequence system
U2 rms value of the positive sequence system
a1 = e i120° rotation operator for 120o
a2 = e i240° rotation operator for 240o
Explanation:
a2U2means:
Rotate the voltage vector U2 by 240o in positive direction (to the left).

SEG Electronics GmbH Manual MRU3-2
16 DOK-TD-MRU3-2, Rev. B
4.4.4 Negative sequence system of a symmetrical voltage system
Figure 4.3: Graphical determination of the negative sequence system in a symmetrical system
Figure 4.3 shows a symmetrical vector system. As indicated in the calculation the MRU3-2 forms
the negative sequence system. For this it rotates per software both voltage vectors U2 by 240o and
U3 by 120o and adds them. Acc. to definition the result of the vector must be multiplied by 1/3. In
this example the sum equals zero. Conclusion: the source system is symmetrical.
4.4.5 System with voltage unbalance
Figure 4.4: Graphical determination of the negative sequence system in an asymmetrical system
Figure 4.4 shows the voltage vectors of an asymmetrical grid. A residual negative sequence sys-
tem voltage, which is not zero, is calculated in this example. Should this residual voltage exceed
the set threshold, which is indicated as rms value, the relay trips after the preselected time delay.
For the exact rotation of the current vectors by 120o or 240o the system frequency has to be pre-
cisely adjusted.

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 17
4.4.6 Zero sequence system
To decide whether a vector system is symmetrically, the point, the symmetry has to refer to, is al-
ways to be mentioned. Usually this point is the earth potential.
When an earth fault occurs in an isolated or compensated grid, it does not influence the relative
position of the three voltage vectors to each other, mains operation can be maintained. The vector
peak of the missing phase is forced on the earth potential. For an observer who takes the earth
potential as reference, the star point shifts by the amount of the missing phase. For him the voltage
vector system is not anymore symmetrical. The exact measure of the shifting results from replacing
this system in symmetrical components in the developed zero sequence system.
Note:
Shall the relay evaluate the zero sequence system it is absolutely necessary that the voltage trans-
formers and the MRU3-2 are wired in star connection. The star points must be earthed; furthermore
the MRU2-2 must be set to Y-connection. In delta connection no zero sequence system evaluation
is possible and thus no earth fault detection.
When only the phase-to-phase voltages are measured, the vector star point is not known, thus also
the position of the star point in regard to the earth potential cannot be defined.
Figure 4.5: Zero point shifting after earth fault in the isolated grid

SEG Electronics GmbH Manual MRU3-2
18 DOK-TD-MRU3-2, Rev. B
5.Operations and settings
5.1 Display
Function
Display shows
Pressed pushbutton
Corre-
sponding
LED
Normal operation
WW
Measured operating val-
ues
Actual measured value
<SELECT/RESET>
one time for each value
L1, L2, L3,
U1, U2, U0
Phasenfolge
123; 321
PS
Transformer ratio of the
CT’s
(SEK) 1.01-6500=prim
<SELECT/RESET><+><->
L1, L2, L3
Setting values
Star/delta connection
Y/DELT
<SELECT/RESET><+><->
D/Y
Mains frequency
f = 50 Hz, f = 60 Hz
v = 50 Hz, v = 60 Hz
<SELECT/RESET><+><->
fN
Parameter switch/external
trigger for the fault record-
er
SET1, SET2, B_S2,
R_S2, B_FR, R_FR,
S2_FR
<SELECT/RESET><+><->
P2
Switch-over LED flash
No LED flash
FLSH
NOFL
<SELECT/RESET><+><->
U</U> 1-phase/3-phase
tripping
U<>1/U<>3
<SELECT/RESET><+><->
1/3
undervoltage (low set)
tripping delay of low set
element
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U<
tU<
undervoltage (high set)
tripping delay of high set
element
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U<<
tU<<
overvoltage (low set)
tripping delay of low set
element
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U>
tU>
overvoltage (high set)
tripping delay of high set
element
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U>>
tU>>
positive-phase sequence
system undervoltage U1<;
trip delay tU1<
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U1<
tU1<
positive-phase sequence
system overvoltage U1>;
trip delay tU1>
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U1>
tU1>
negative-phase sequence
system overvoltage U2>;
trip delay tU2>
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U2>
tU2>
zero-phase sequence sys-
tem U0>
trip delay tU0>
Setting value in volt
Setting value in seconds
<SELECT/RESET><+><->
one time for each value
U0>
tU0>
Function blocking
EXIT
<+> until max. setting
<-> until min. setting
LED of
blocked pa-
rameter
Slave adresse of serial in-
terface
1 - 32
<SELECT/RESET><+><->
RS
Baud-Rate 1)
1200-9600
<SELECT/RESET><+><->
RS
Parity-Check 1)
even odd no
<SELECT/RESET><+><->
RS
Recorded fault data:
Star-connection: L1, L2, L3
Symmetrical components:
U1, U2, U0
Tripping values in volt
<SELECT/RESET><+><->
one time for each phase
L1, L2, L3;
U1, U2, U0,
U<, U<<,
U>, U>>,

Manual MRU3-2 SEG Electronics GmbH
DOK-TD-MRU3-2, Rev. B 19
Function
Display shows
Pressed pushbutton
Corre-
sponding
LED
U1<, U1>,
U2>, U0>
Delta-connection: L1/L2,
L2/L3, L3/L1
symmetrical components:
U1, U2
Tripping values in volt
<SELECT/RESET><+><->
one time for each phase
L1, L2, L3,
U1, U2, U<,
U<<, U>,
U>>, U1<,
U1>, U2>
Save parameter?
SAV?
<ENTER>
Save parameter!
SAV!
<ENTER> for about 3 s
Delete failure memory
wait
<-> <SELECT/RESET>
Enquiry failure memory
FLT1; FLT2.....
<-><+>
L1, L2, L3
U<, U<<,
U>, U>>
Trigger signal for thefault
recorder
TEST, P_UP, A_PI, TRIP
<SELECT/RESET> <+><->
FR
Function
Display shows
Pressed pushbutton
Correspond-
ing LED
Number of fault occurences
S = 2, S = 4, S = 8
<SELECT/RESET> <+><->
FR
Display of date and time
Y = 99, M = 10,
D = 1,
h = 12, m = 2, s = 12
<SELECT/RESET> <+><->
Software version
First part (e. g. D02-)
Second part (e. g. 6.01)
<TRIP> one time for each
part
Manual trip
TRI?
<TRIP> three times
Inquire password
PSW?
<SELECT/RESET>/
<+>/<->/<ENTER>
Relay tripped
TRIP
<TRIP> or fault tripping
Secret password input
XXXX
<SELECT/RESET>/
<+>/<->/<ENTER>
System reset
WW
<SELECT/RESET>
for about 3 s
1) only Modbus
Table 5.1: Possible indication messages on the display
5.2 Setting procedure
In this paragraph the settings for all relay parameters are described in detail. For parameter setting
a password has to be entered first (please refer to 4.4 of description "MR-Digital Multifunctional Re-
lays").

SEG Electronics GmbH Manual MRU3-2
20 DOK-TD-MRU3-2, Rev. B
5.3 System parameter
5.3.1 Display of residual voltage UE as primary quantity (Uprim/Usec)
The residual voltage can be shown as primary measuring value. For this parameter the transfor-
mation ratio of the VT has to be set accordingly. If the parameter is set to "sec", the measuring val-
ue is shown as rated secondary voltage.
Example:
The voltage transformer used is of 10 kV/100 V. The transformation ratio is 100 and this value has
to be set accordingly. If still the rated secondary voltage should be shown, the parameter is to be
set to 1.
5.3.2 D/Y –Switch - over
Depending on the mains voltage conditions, the input voltage transformers can be operated in delta
or Y connection. Changeovers are effected via the <+> and the <-> keys and stored with
<ENTER>.
5.3.3 Setting of nominal voltage
For proper functioning it is necessary to first adjust the rated frequency (50 or 60 Hz).
It can be selected between „f = 50 Hz“, „f = 60 Hz“ or „v = 50 Hz“, “v = 60 Hz”.
The difference lies in the method of voltage measuring.
With the setting "v = 50 Hz“ or “v = 60 Hz” voltage measuring is independent of the existing fre-
quency. This means, the voltage value can be correctly measured between 40 Hz and 70 Hz with-
out adverse effects from the frequency.
With the setting "f“ = 50/60 Hz the measured voltage value is influenced by the frequency. (see Ta-
ble 5.2)
Figure 5.1: Impairment of voltage measuring
This difference in settings is required for the fault recorder. If the fault recorder is to be used, the
setting must be f = 50 Hz or f = 60 Hz.
At 50 Hz or 60 Hz the fault recorder determines 16 measured values per period. With the setting
"v = 50 Hz" or “v = 60 Hz” 16 measured values of the presently measured frequency would always
be determined. The disturbance recorder would not indicate any frequency changes and thus ren-
der incorrect measuring results.