Seg MRU3-1 User manual

MRU3-1 –AC voltage relay

2TB MRU3-1 12.00 E
Contents
1 Introduction and application
2 Features and characteristics
3 Design
3.1 Connections
3.1.1 Analog input circuits
3.1.2 Blocking input
3.1.3 Reset input
3.1.4 Output relays
3.1.5 Fault recorder
3.1.6 Parameter settings
3.2 LEDs
3.3 Front plate
4 Working principle
4.1 Analog circuits
4.2 Digital circuits
4.3 Voltage supervision
4.3.1 Selection of star or delta connection
4.4 Blocking function
5 Operations and settings
5.1 Display
5.2 Setting procedure
5.3 Systemparameter
5.3.1 Display of residual voltage UEas
primary quantity (Uprim/Usec)
5.3.2 ∆/Y – Switch over
5.3.3 Setting of nominal frequency
5.3.4 Display of the activation storage
5.3.5 Parameter switch/external triggering for
the fault recorder
5.4 Protection parameters
5.4.1 1-phase or 3-phase U</U>-
tripping
5.4.2 Parameter setting of over- and under-
voltage supervision
5.4.3 Adjustment of the slave address
5.4.4 Setting of Baud-rate (applies for Modbus-
Protocol only)
5.4.5 Setting of parity (applies for Modbus-
Protocol only)
5.5 Parameter for the fault recorder
5.5.1 Adjustment of the fault recorder
5.5.2 Number of the fault recordings
5.5.3 Adjustment of trigger occurences
5.5.4 Pre-trigger time (Tpre)
5.6 Date and time
5.6.1 Adjustment of the clock
5.7 Indication of measuring values
5.7.1 Measuring indication
5.7.2 Unit of the measuring values displayed
5.7.3 Indication of fault memory data
5.8 Fault memory
5.9 Additional functions
5.9.1 Setting procedure for blocking the
protection functions
5.9.2 Reset
5.9.3 Erasure of fault storage
6 Relay testing and commissioning
6.1 Power-On
6.2 Testing the output relays
6.3 Checking the set values
6.4 Secondary injection test
6.4.1 Test equipment
6.4.2 Example of the test circuit
6.4.3 Checking the input circuits and
measuring functions
6.4.4 Checking the operating and resetting
values of the over/undervoltage
functions
6.4.5 Checking the relay operating time of the
over/undervoltage functions
6.4.6 Checking the external blocking and reset
functions
6.5 Primary test
6.6 Maintenance
7 Technical Data
7.1 Measuring input circuits
7.2 Common data
7.3 Setting ranges and steps
7.3.1 Interface parameter
7.3.2 Parameter for the fault recorder
7.4 Output relays
8 Order form

TB MRU3-1 12.00 E 3
1 Introduction and application
The voltage supervision relay MRU3-1 protects electri-
cal power generators, consumers or operating com-
ponents generally against over- or undervoltages.
Among other applications the relay can be used:
•for detection of over- or undervoltages in power gen-
rating plants and energy supply systems
•to protect generators against critical overvoltages in
case of defective voltage regulators
•as undervoltage protection for motors
•as generator stator earth fault protection
•as over- and undervoltage protection with evaluating
the symmetrical components (MRU1-2, detailed in-
formation on this type can be found in the relevant
technical description)
There is also a similar protection relay IRU1 available
in a more simpler design, i.e. with less function, with-
out display and without serial interface.
Important:
For additional common data of all MR-relays please
refer to technical description "MR - Digital Multifunc-
tional Relays".
2 Features and characteristics
•Microprocessor technology with watchdog,
•digital filtering of the measured values by using dis-
crete Fourier analysis to suppress higher harmonics
and d.c. components induced by faults or system
operations,
•two parameter sets,
•voltage supervision each with two step under-/ and
overvoltage detection,
•Completely independent time settings for voltage su-
pervision
•display of all measuring values and setting parame-
ters for normal operation as well as tripping via a
alphanumerical display and LEDs,
•display of measuring values as primary quantities
•1-phase or 3-phase tripping criterion for the U</U>
step,
•Storage and display of tripping values in a fault
memory (voltage-failure safe),
•recording of up to eight fault occurences 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 complience with VDE 0435, part 303 and IEC
255,
•serial data exchange via RS485 interface possible;
alternatively with SEG RS485 Pro-Open Data Proto-
col or Modbus Protocol.

4TB MRU3-1 12.00 E
3 Design
3.1 Connections
Figure 3.1: Connection of the MRU3-1 to phase-to-phase voltage
Note: Connection of phase-to-neutral voltage is possible too.
Figure 3.2: Voltage transformer in V-connection
3.1.1 Analog input circuits
The external wiring of the measuring circuits are shown
in the connection diagram. The analog input voltages
are galvanically decoupled by the input transformers of
the device, then filtered and finally fed to the analog
digital converter. The measuring circuits can be con-
nected in star or delta connection.
3.1.2 Blocking input
When required to inhibit functions of the relay, the
auxiliary voltage has to be switched to D8/E8. Please
refer to chapter 4.4.
3.1.3 Reset input
Please refer to chapter 5.9.2.

TB MRU3-1 12.00 E 5
3.1.4 Output relays
The MRU3-1 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.
3.1.5 Fault recorder
The MRU3-1 has a fault value recorder which records
the measured analog values as instantaneous values.
The instantaneous values
UL1; UL2; UL3 for star connection
or U12; U23; U21 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. It is
possible to store 1 - 8 fault occurences with a total re-
cording time of 16 s (with 50 Hz) and 13.33 s (with
60 Hz) per channel.
Storage division
Independent of the recording time, the entire storage
capacity can be divided into several cases of distur-
bance with a shorter recording time each. In addition,
the deletion behaviour of the fault recorder can be in-
fluenced.
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 record-
ings 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 num-
ber of partial segments is reserved in the complete
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 records 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
Since memory spaces 6, 7 and 8 are occupied, this
example shows that the memory has been assigned
more than eight recordings. This means that No. 6 is
the oldest fault recording and No. 4 the most recent
one.
trigger occurence
recording duration
Tpre
[s]
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.

6TB MRU3-1 12.00 E
3.1.6 Parameter settings
System parameters
Uprim/Usek Primary/secondary measured value
display of the voltage transformers
∆/ Y Selection of switching groups
fNRated frequency
P2|FR Parameter switch/ext. triggering for the
fault recorder
LED-Flash Suppression of LED flashing after
activation
Protection parameters
1/3 1-phase U</U> or 3-phase U</U>
tripping
U< Tripping value for undervoltage low set
element
tU< Tripping delay time for undervoltage low
set element
U<< Tripping value for undervoltage high set
element
tU<< Tripping delay time for undervoltage
high
set element
U> Tripping value for overvoltage low set
element
tU> Tripping delay time for overvoltage low
set element
U>> Tripping value for overvoltage high set
element
tU>> Tripping delay time for overvoltage high
set element
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 LEDs
All LEDs (except LED RS, FR and P2) are two-coloured.
The LEDs on the left side, next to the alphanumerical
display light up green during measuring and red after
tripping.
The LEDs below the push button <SELECT/RESET> are
lit green during setting and inquiry procedure of the
setting values which are printed on the left side next to
the LEDs. The LEDs will light up red after parametrizing
of the setting values next to their right side.
The LED marked with letters RS lights up during setting
of the slave address of the device for serial data com-
munication.
The LED marked with the letters FR is alight while the
fault recorder is being adjusted.
If the ! LED is displayed, date and time are shown.
3.3 Front plate
Figure 3.5: Front plate MRU3-1

TB MRU3-1 12.00 E 7
4 Working principle
4.1 Analog circuits
The input voltages are galvanically insulated by the in-
put transformers. The noise signals caused by inductive
and capacitive coupling are supressed 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 MRU3-1 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 pro-
tected 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 sup-
press high frequency harmonics and d.c. components
caused by fault-induced transients or other system dis-
turbances. The microprocessor continuously compares
the measured values with the preset thresholds stored
in the parameter memory (EEPROM). If a fault occures
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 - Electrically 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 "watch-
dog" timer. In case of a failure the watchdog timer re-
sets the microprocessor and gives an alarm signal via
the output relay "self supervision".
4.3 Voltage supervision
The voltage relay MRU3-1 protects electrical genera-
tion systems, consumers and appliances in general
against over- and/or undervoltage. The relay is
equipped with an independent, 2-step over- (U>, U>>)
and undervoltage supervision (U<, U<<) with sepa-
rately adjustable tripping values and delay times. Volt-
age 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 volt-
ages in case of a star connection with the preset limit
values.
With the MRU3-1 the highest voltage is always evalu-
ated for overvoltage supervision and the lowest volt-
age for undervoltage 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 or 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 or tripping takes place if all three
phases have fallen short of the tripping value.
U<<: Activation or tripping takes place if one phase
has fallen short of the tripping value.
U>: Activation or tripping takes place if all three
phases have exceeded the tripping value.
U>> Activation or tripping takes place if one phase
has exceeded the tripping value.

8TB MRU3-1 12.00 E
4.3.1 Selection of star or delta
connection
All six connections of the input voltage transformers are
led to screw terminals. The nominal voltage of the de-
vice is equal to the nominal voltage of the input trans-
formers. Dependent on the application the input trans-
formers 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
reduced by 1/ 3. During parameter setting the con-
nection configuration either Y or delta has to be ad-
justed.
)!
)"
)#
)$
)%
)&
7
7 !
7!
Sec. winding of
mains V.T.
=
>
?
Figure 4.1: Input v.t.s in delta connection (D)
)!
)"
)#
)$
)%
)&
7
7
7!
Sec. winding of
mains V.T.
=
>
?
Figure 4.2: Input v.t.s in star connection (Y)
4.4 Blocking function
No. Dynamic Behaviour U</<< U>/>>
1 voltage to external
blocking input is ap-
plied
free pro-
gramma-
ble
free pro-
gramma-
ble
2 blocking input is
released
released
instanta-
neously
released
instanta-
neously
3 supply voltage is
switched on
blocked
for
200 ms
blocked
for 200
ms
4 3ph measuring volt.
is suddenly applied
released released
5 one or several meas-
uring voltages are
switched off suddenly
(phase failure)
released released
Table 4.1: Dynamic behaviour of MRU3-1 functions
Blocking function set in compliance with require-
ments:
The MRU3-1 has an external blocking input. By apply-
ing the auxiliary voltage to input D8/E8, the re-
quested protection functions of the relay are blocked
(refer to chapter 5.9.1)

TB MRU3-1 12.00 E 9
5 Operations and settings
5.1 Display
Function Display shows Pressed pushbutton Corresponding LED
Normal operation SEG
Measured operating values Actual measured values <SELECT/RESET> one time
for each value
L1, L2, L3,
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><+><-> ∆/Y
Parameter switch/ext. triggering
for the fault recorder SET1, SET2, B_S2, R_S2,
R_S2, B_FR, R_FR, S2_FR
<SELECT/RESET><+><-> P2
Switch-over LED flash
No LED flash
FLSH
NOFL
<SELECT/RESET>
<+><->
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>>
rated frequency setting value in Hz <SELECT/RESET><+><-> fN
U</U> 1-phase/3-phase U<>1/U<>3 <SELECT/RESET><+><-> 1/3
Blocking function EXIT <+> until max. setting value
<-> until min. setting value
LED of blocked
parameter
Slave address of serial interface 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: U1, U2, U3
tripping values in Volt <SELECT/RESET><+><->
one time for each phase
L1, L2, L3, U<, U<<,
U>, U>>
delta-connection: U12, U23, U31 tripping values in Volt <SELECT/RESET><+><->
one time for each phase
L1, L2, L3, U<, U<<,
U>, U>>
Save parameter? SAV? <ENTER>
Save parameter! SAV! <ENTER> for about 3 s
Delete fault memory wait <-> <SELECT/RESET>
Enquiry fault memory FLT1; FLT2..... <-><+> L1, L2, L3
U<, U<<, U>, U>>
Trigger signal for the fault recorder TEST, P_UP, A_PI, TRIP <SELECT/RESET> <+><-> FR
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-)
Sec. 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 SEG <SELECT/RESET>
for about 3 s
1) only Modbus
Table 5.1: Possible indication messages on the display

10 TB MRU3-1 12.00 E
5.2 Setting procedure
For parameter setting a password has to be entered
first (please refer to 4.4 of description "MR-Digital Mul-
tifunctional Relays").
5.3 Systemparameter
5.3.1 Display of residual voltage UEas
primary quantity (Uprim/Usec)
The residual voltage can be shown as primary measur-
ing value. For this parameter the transformation ratio of
the VT has to be set accordingly. If the parameter is set
to "sec", the measuring value is shown as rated secon-
dary voltage.
Example:
The voltage transformer is used for 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. Change-overs are effected via the <+>
and the <-> keys and stored with <ENTER>.
5.3.3 Setting of nominal frequency
For proper functioning it is necessary to first adjust the
rated frequency (50 oder 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 frequency.
This means, the voltage value can be correctly meas-
ured between 40 Hz and 70 Hz without adverse ef-
fects from the frequency.
With the setting "f“ = 50/60 Hz the measured voltage
value is influenced by the frequency. (see Table 5.2)
Declination of measuring value at 50Hz
97,5
98,0
98,5
99,0
99,5
100,0
100,5
44 46 48 50 52 54 56
[%]
[Hz]
Declination of measuring value at 60Hz
97,5
98,0
98,5
99,0
99,5
100,0
100,5
54 56 58 60 62 64 66
[%]
[Hz]
This difference in settings is required for the fault re-
corder. 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 render incorrect measuring results.
Setting v = 50 f = 50 v = 60 f = 60
Rated frequency* 50 Hz 50 Hz 60 Hz 60 Hz
Influence on voltage
measurement
none 0.5..1%/Hz
(see table 5.1)
none 0.5..1%/Hz
(see table 5.1)
Fault recorder Recording
distorted**
Recording
correct***
Recording
distorted**
Recording
correct***
Influence on all other
functions
none none none none
Table 5.2: Deviation of measured value at 50 Hz or 60 Hz
* Setting is important for correct recording of fault recorder
** Sample rate is variably adjusted to the momentarily measured frequency. 16 samples are always measured in one period.
*** Sample rate setting is fixed to 50 Hz or 60 Hz. 16 samples per 20 ms or 16.67 ms are always measured.

TB MRU3-1 12.00 E 11
5.3.4 Display of the activation storage
If after an activation the existing current drops again
below the pickup value, e.g. U<, without a trip has
been initiated, LED U< signals that an activation has
occured by flashing fast. The LED keeps flashing until it
is reset again (push button <RESET>). Flashing can be
suppressed when the parameter is set to NOFL.
5.3.5 Parameter switch/external
triggering for the fault recorder
By means of the parameter-change-over switches it is
possible to activate two different parameter sets.
Switching over of the parameter sets can either be
done by means of software or via the external inputs
RESET or blocking input. Alternatively, the external in-
puts can be used for Reset or blocking of the triggering
of the fault recorder.
Software-
parameter
Blocking input
used as
RESET input
used as
SET1 Blocking input RESET input
SET2 Blocking input RESET input
B_S2 Parameter switch RESET input
R_S2 Blocking input Parameter switch
B_FR External trigger-
ing of the fault
recorder
Reset input
R_FR Blocking input External trigger-
ing of the fault
recorder
S2_FR Parameter switch External trigger-
ing of the fault
recorder
With the settings SET1 or SET2 the parameter set is
activated by software. Terminals C8/D8 and D8/E8
are then available as external reset input or blocking
input.
With the setting B_S2 the blocking input (D8, E8) is
used as parameter-set change-over switch. With the
setting R_S2 the reset input (D8, E8) is used as pa-
rameter-set change-over switch. With the setting B_FR
the fault recorder is activated immediately by using the
blocking input. On the front plate the LED FR will then
light up for the duration of the recording. With the set-
ting R_FR the fault recorder is activated via the reset
input.
With the setting S2_FR parameter set 2 can be acti-
vated via the blocking input and/or the fault recorder
via the reset input.
The relevant function is then activated by applying the
auxiliary voltage to one of the external inputs.
Important note:
When functioning as parameter change over facility,
the external input RESET is not available for resetting.
When using the external input BLOCKING the protec-
tion functions must be deactivated by software block-
ing separately (refer to chapter 5.9.1).
5.4 Protection parameters
5.4.1 1-phase or 3-phase U</U>-
tripping
Switching-over of the parameter permits selection be-
tween 1-phase and 3-phase tripping of the U</U>
steps.
Keys <+> or <-> are used to change the value and
<ENTER> to store it.
Note
When the MRU3-1 is to be used for measuring the re-
sidual voltage in systems with isolated or compensated
neutral or as generator earth fault protection, the
measuring voltage has to be applied to terminals
A3-A4. Undervoltage functions U< and U<< have to
be set to "EXIT" and overvoltage functions U> and U>>
have to be adjusted to the required pickup values.
The frequency must be set to 50 or 60 Hz. The pa-
rameter 1-phase or 3-phase tripping mut be set to
U<>1 (1-phase tripping).

12 TB MRU3-1 12.00 E
5.4.2 Parameter setting of over- and
undervoltage supervision
The setting procedure is guided by two coloured LEDs.
During setting of the voltage thresholds the LEDs U<,
U<<, U> and U>> are lit green. During setting of the
trip delays tU>, tU>>, tU< and tU<< the according LEDs light
up red.
Thresholds of the voltage supervision
During setting of the threshold U>, U>>, U< and U<<
the displays shows the voltages directly in volt. The
thresholds can be changed by the <+> <-> push but-
tons and stored with <ENTER>.
The undervoltage supervision (U< and U<<) as well as
the overvoltage supervision (U> and U>>) can be de-
activated by setting the threshold to "EXIT".
Tripping delay of voltage supervision
During setting of the tripping delays tU<, tU<<, tU> and tU>>
the display shows the value directly in seconds. The
tripping delay is changed via the push button <+>
and <-> in the range of 0,04 s to 50 s and can be
stored with the push button <ENTER>.
When setting the tripping delay to "EXIT" the value is
infinit meaning only warning, no tripping.
5.4.3 Adjustment of the slave address
By pressing push buttons <+> and <-> the slave ad-
dress can be set in the range of 1 - 32. During this ad-
justment the LED RS lights up.
5.4.4 Setting of Baud-rate (applies for
Modbus-Protocol only)
Different transmission rates (Baud rate) can be set for
data transmission via Modbus Protocol.
The rate can be changed by push buttons <+> and
<-> and saved by pressing <ENTER>.
5.4.5 Setting of parity (applies for
Modbus-Protocol only)
The following three parity settings are possible :
•"even" = even parity
•"odd" = odd parity
•"no" = no parity check
The setting can be changed by push buttons <+> and
<-> and saved by pressing <ENTER>.
5.5 Parameter for the fault recorder
5.5.1 Adjustment of the fault recorder
The MRU3-1 is equipped with a fault recorder (see
chapter 3.1.5). Three parameters can be determined.
5.5.2 Number of the fault recordings
The max. recording time is 16 s at 50 Hz or 13.33 s
at 60 Hz.
The number of max. recordings requested has to be
determined in advance. There is a choice of (1)* 2,
(3)* 4 or (7)* 8 recordings and dependent on this the
duration of the individual fault recordings is defined,
i.e.
(1)* 2 recordings for a duration of 8 s (with 50 Hz)
(6.66 s with 60 Hz)
(3)* 4 recordings for a duration of 4 s (with 50 Hz)
(3.33 s with 60 Hz)
(7)* 8 recordings for a duration of 2 s (with 50 Hz)
(1,66 s with 60 Hz)
* is written over when a new trigger signal arrives
Caution:
If the fault recorder is used, the frequency should be
set to f = 50 Hz or f = 60 Hz (see chapter 5.3.3).

TB MRU3-1 12.00 E 13
5.5.3 Adjustment of trigger occurences
There is a choice between four different occurences:
P_UP (PickUP) Storage is initiated after recognition
of a general activation.
TRIP Storage is initiated after a trip has
occured.
A_PI (After Pickup) Storage is initiated after the last
activation threshold was fallen
short of.
TEST Storing is activated by simultaneous
actuation of the keys <+> and <->.
During the recording time the
display shows “Test”.
5.5.4 Pre-trigger time (Tpre)
By the time Tpre it is determined which period of time
prior to the trigger occurence should be stored as well.
It is possible to adjust a time between 0.05s and the
max. recording interval (2, 4 and 8s). With keys <+>
and <-> the values can be changed and with
<ENTER> be saved.
5.6 Date and time
5.6.1 Adjustment of the clock
When adjusting the date and time, LED !lights up.
The adjustment method is as follows:
Date : Year Y=00
Month M=01
Day D=01
Time : Hour h=00
Minute m=00
Second s=00
The clock starts with the set date and time as soon as
the supply voltage is switched on. The time is safe-
guarded against short-term voltage failures (min. 6
minutes).
Note:
The window for parameter setting is located behind
the measured value display. The parameter window
can be accessed via the <SELECT/RESET> key.
5.7 Indication of measuring values
5.7.1 Measuring indication
In normal operation the following measuring values
can be displayed.
•Voltages (LED L1, L2, L3 green)
•In star connection all phase-to-neutral voltages
•In delta connection all phase-to-phase voltages
5.7.2 Unit of the measuring values
displayed
The measuring values can optionally be shown in the
display as a multiple of the "sek" rated value (x ln) or
as primary current (A). According to this the units of the
display change as follows:
Indication as Range Unit
Sec. voltage 000V - 999V V
Primary voltage .00V – 999V
1k00 – 9k99
10k0 – 99k0
100k – 999k
1M00 –-
3M00
V
kV
kV
kV
MV
Table 5.3: Units of the display
5.7.3 Indication of fault memory data
All faults detected by the relay are indicated on the
front plate optically. For this purpose, the three LEDs
(L1, L2, L3) and the four function LEDs (U<, U<<, U>,
U>>) are equipped at MRU3-1. Not only fault mes-
sages are transmitted, the display also indicates the
tripped protection function. If, for example an overcur-
rent occurs, first the respective phase LED will light up.
LED I> lights up at the same time. After tripping the
LEDs are lit permanently.

14 TB MRU3-1 12.00 E
5.8 Fault memory
When the relay is energized or is energized or trips,
all fault data and times are stored in a non-volatile
memory manner. The MRU3-1 is provided with a fault
value recorder for max. five fault occurrences. In the
event of additional trippings always the oldest data set
is written over.
For fault indication not only the trip values are re-
corded but also the status of LEDs. Fault values are in-
dicated when push buttons <-> or <+> are pressed
during normal measuring value indication.
•Normal measuring values are selected by pressing
the <SELECT/RESET> button.
•When then the <-> button is pressed, the latest fault
data set is shown. By repeated pressing the <->
button the last but one fault data set is shown etc.
For indication of fault data sets abbreviations FLT1,
FLT2, FLT3, ... are displayed (FLT1 means the latest
fault data set recorded). At the same time the pa-
rameter set active at the occurence is shown.
•By pressing <SELECT/RESET> the fault measuring
values can be scrolled.
•By pressing <+> it can be scrolled back to a more
recent fault data set. At first FLT8, FLT7, ... are al-
ways displayed.When fault recording is indicated
(FLT1 etc), the LEDs flash in compliance with the
stored trip information, i.e. those LEDs which
showed a continuous light when the fault occured
are now blinking to indicate that it is not a current
fault. LEDs which were blinking during trip condi-
tions, (element had picked up) just briefly flash.
•If the relay is still in trip condition and not yet reset
(TRIP is still displayed), no measuring values can be
shown.
•To delete the trip store, the push button combina-
tion <SELECT/RESET> and <->, has to be pressed
for about 3s. The display shows “wait”.
Recorded fault data:
Measuring Displayed value Correspond-
ing LED
Voltage L1; L2; L3; star
L1/L2; L2/L3: L3/L1
delta
L1; L2; L3
Time stamp
Date: Y = 99
M = 03
D = 10
!
!
!
Time: h = 17
m = 21
s = 14
!
!
!

TB MRU3-1 12.00 E 15
5.9 Additional functions
5.9.1 Setting procedure for blocking the
protection functions
The blocking function of the MRU3-1 can be set ac-
cording to requirement. By applying the aux. voltage
to D8/E8, the functions chosen by the user are
blocked. Setting of the parameter should be done as
follows:
•When pressing push buttons <ENTER> and <TRIP>
at the same time, message "BLOC" is displayed (i.e.
the respective function is blocked) or "NO_B" (i.e.
the respective function is not blocked). The LED allo-
cated to the first protection function U< lights red.
•By pressing push buttons <+> <-> the value dis-
played can be changed.
•The changed value is stored by pressing <ENTER>
and entering the password.
•By pressing the <SELECT/RESET> push button, any
further protection function which can be blocked is
displayed.
•Thereafter the menu is left by pressing
<SELECT/RESET> again.
•If the <SELECT/RESET> key is actuated again, the
blocking menu is left and the assignment mode is
accessed.
Function Description Display LED
U< Undervoltage step 1 BLOC green
U<< Undervoltage step 2 BLOC green
U> Overvoltage step 1 NO_B green
U>> Overvoltage step 2 NO_B green
Table 5.4: Blocking function for two parameter sets
Assignment of the output relays:
Unit MRU3-1 has five output relays. The fifth output re-
lay is provided as permanent alarm relay for self su-
pervision is normally on. Output relays 1 - 4 are nor-
mally off and can be assigned as alarm or tripping re-
lays to the voltage functions which can either be done
by using the push buttons on the front plate or via se-
rial interface RS485. The assignment of the output re-
lays is similar to the setting of parameters, however,
only in the assignment mode. The assignment mode
can be reached only via the blocking mode.
By pressing push button <SELECT/RESET> in blocking
mode again, the assignment mode is selected.
The relays are assigned as follows: LEDs U<, U<<, U>
and U>> are two-coloured and light up green when
the output relays are assigned as alarm relays and tU<,
tU<<, tU>, tU>>, red as tripping relays.
Definition:
Alarm relays are activated at pickup.
Tripping relays are only activated after elapse of the
tripping delay.
After the assignment mode has been activated, first
LED U< lights up green. Now one or several of the
four output relays can be assigned to under voltage
element U< as alarm relays. At the same time the se-
lected alarm relays for under voltage element 1 are
indicated on the display. Indication "1_ _ _" means
that output relay 1 is assigned to this under voltage
element. When the display shows "_ _ _ _", no alarm
relay is assigned to this under voltage element. The as-
signment of output relays 1 - 4 to the current elements
can be changed by pressing <+> and <-> push but-
tons. The selected assignment can be stored by press-
ing push button <ENTER> and subsequent input of the
password. By pressing push button <SELECT/RESET>,
LED U< lights up red. The output relays can now be
assigned to this voltage element as tripping relays.
Relays 1 - 4 are selected in the same way as de-
scribed before. By repeatedly pressing of the
<SELECT/RESET> push button and assignment of the
relays all elements can be assigned separately to the
relays. The assignment mode can be terminated at any
time by pressing the <SELECT/RESET> push button for
some time (abt. 3 s).
Note:
•The function of jumper J2 described in general de-
scription "MR Digital Multifunctional Relays" does
not apply for MRU3-1. For relays without assign-
ment mode this jumper is used for parameter setting
of alarm relays (activation at pickup or tripping).
A form is attached to this description where the setting
requested by the customer can be filled-in. This form is
prepared for telefax transmission and can be used for
your own reference as well as for telephone queries.

16 TB MRU3-1 12.00 E
5.9.2 Reset
All relays have the following three possibilities to reset
the display of the unit as well as the output relay at
jumper position J3=ON.
Manual Reset
•Pressing the push button <SELECT/RESET> for some
time (about 3 s)
Electrical Reset
•Through applying auxiliary voltage to C8/D8
Software Reset
•The software reset has the same effect as the
<SELECT/RESET> push button (see also communica-
tion protocol of RS485 interface)
The display can only be reset when the pickup is not
present anymore (otherwise "TRIP" remains in display).
During resetting of the display the parameters are not
affected.
5.9.3 Erasure of fault storage
To delete the trip store, the push button combination
<SELECT/RESET> and <->, has to be pressed for
about 3s. The display shows “wait”.
Relay function Output relays Display- Corres-
ponding
1234IndicationLED
U< Alarm _ _ _ _ U<; green
tU< Tripping X _ _ 3 _ tU< red
U<< Alarm _ _ _ _ U<< green
tU<< Tripping X _ _ _ 4 tU<< red
U> Alarm _ _ _ _ U> green
tU> Tripping X 1 _ _ _ tU> red
U>> Alarm _ _ _ _ U>> green
tU>> Tripping X _ 2 _ _ tU>> red
Table 5.5: Example of assignment matrix of the output relay (defaults settings)

TB MRU3-1 12.00 E 17
6 Relay testing and
commissioning
The following test instructions should help to verify the
protection relay performance before or during commis-
sioning of the protection system. To avoid a relay
damage and to ensure a correct relay operation, be
sure that:
•The auxiliary power supply rating corresponds to the
auxiliary voltage on site.
•The rated frequency and rated voltage of the relay
correspond to the plant data on site.
•The voltage transformer circuits are connected to the
relay correctly.
•All signal circuits and output relay circuits are con-
nected correctly.
6.1 Power-On
NOTE!
Prior to switch on the auxiliary power supply, be sure
that the auxiliary supply voltage corresponds to the
rated data on the type plate.
Switch on the auxiliary power supply to the relay and
check that the message "ISEG" appears on the display
and the self supervision alarm relay (watchdog) is en-
ergized (Contact terminals D7 and E7 closed).
It may happen that the relay is tripped because of un-
der- voltage condition after power-on. (The message
"TRIP" on the display and LED L1, L2, L3 and U< light
up red). An undervoltage condition has been detected
after power-on, because no input voltages are applied
to the relay. In this case:
•Press the push button <ENTER>, thus entering into
the setting mode. Now set the parameters U< and
U<< to "EXIT" to block the undervoltage functions. Af-
ter that, press the <SELECT/RESET> for app. 3 s to
reset the LEDs and "TRIP" message.
•The undervoltage tripping after power on can also
be eliminated by applying three phase rated volt-
ages after power-on and reset the LED and "TRIP"
message.
•Apply auxiliary voltage to the external blocking input
(Terminals E8/D8) to inhibit the undervoltage func-
tions (refer to 6.5) and press the <SELECT/RESET>
for app. 3 s to reset the LEDs and "TRIP" message.
(see chapter 5.9.1)
6.2 Testing the output relays
NOTE!
Prior to commencing this test, interrupt the trip circuit to
the circuit breaker if tripping is not desired.
By pressing the push button <TRIP> once, the display
shows the first part of the software version of the relay
(e.g. „D08-“). By pressing the push button <TRIP>
twice, the display shows the second part of the soft-
ware version of the relay (e.g. „4.01“. The software
version should be quoted in all correspondence. Press-
ing the <TRIP> button once more, the display shows
"PSW?". Please enter the correct password to proceed
with the test. The message "TRI?" will follow. Confirm
this message by pressing the push button <TRIP>
again. All output relays should then be activated and
the self supervision alarm relay (watchdog) be deener-
gized one after another with a time interval of 1 sec-
ond. Thereafter, reset all output relays back to their
normal positions by pressing the push button
<SELECT/RESET>.
6.3 Checking the set values
By repeatedly pressing the push button <SELECT>, all
relay set values may be checked. Set value modifica-
tion can be done with the push button <+><-> and
<ENTER>. For detailed information about that, please
refer to chapter 4.3 of the description “MR – Digital
multifunctional relays”.
As relay input energizing quantities, three phase volt-
ages should be applied to MRU3 relay input circuits.
Depending on the system conditions and the voltage
transformer used, three voltages can be connected to
the relay input circuits with either star or delta connec-
tion. In case of a star connection the phase-to-neutral
voltage will be applied to the voltage input circuits,
while the phase-to-phase voltages will be connected to
the voltage input circuits in case of a delta connection.
The voltage input connection must be set as a parame-
ter, and should correspond with the actual voltage in-
put connection:
Star connection: Phase-to-neutral voltages will be
measured and evaluated.
Delta connection: Phase-to-phase voltages will be
measured and evaluated.
NOTE!
For MRU3-1 relay used for earth fault protection be
sure that the frequency set value (f=50/60) has been
selected correctly according to your system frequency
(50 or 60 Hz).
This also applies when using the disturbance recorder
(refer to Chapter 5.3.3).

18 TB MRU3-1 12.00 E
6.4 Secondary injection test
6.4.1 Test equipment
•Voltmeter with class 1 or better
•Auxiliary power supply with the voltage correspond-
ing to the rated data on the type plate
•Three-phase voltage supply unit with frequency regu-
lation (Voltage: adjustable from 0 to ≥2 x UN)
•Timer to measure the operating time (Accuracy class
±10 ms)
•Switching device
•Test leads and tools
6.4.2 Example of the test circuit
For testing of the MRU3-1 relay, a three phase voltage
source is required. Figure 6.1 shows an example of a
three-phase test circuit energizing the MRU3-1 relay
during test. The three phase voltages are applied to
the relay in Y-connection.
Figure 6.1: 3-phase test circuit

TB MRU3-1 12.00 E 19
6.4.3 Checking the input circuits and
measuring functions
Apply three voltages of rated value to the voltage input
circuits (terminals A3 - A8) of the relay. Check the
measured voltages, frequency and vector surge on the
display by pressing the push button <SELECT/RESET>
repeatedly.
The voltages are indicated on the display in volts, at
Y-connection:
•Phase-to-neutral voltages: LED L1, L2, L3
Delta-connection:
•Phase-to-phase voltages: LED L1+L2, L2+L3, L3+L1
Change the voltages around the rated value and
check the measured voltages on the display.
Compare the voltage displayed with the reading at
voltmeter. The deviation for the voltage must not ex-
ceed 1%.
By using an RMS-metering instrument, a greater devia-
tion may be observed if the test voltages contains har-
monics. Because the MRU1 relay measures only the
fundamental component of the input signals, the har-
monics will be rejected by the internal DFFT-digital fil-
ter. Whereas the RMS-metering instrument measures
the RMS-value of the input signals.
6.4.4 Checking the operating and reset-
ting values of the over/under-
voltage functions
Apply three voltages with the rated value and gradu-
ally increase (decrease) the voltages until the relay
starts, i.e. at the moment when the LED U> (or U<)
lights up or the voltage alarm output relay (contact ter-
minals D4/E4) is activated. Read the operating volt-
age indicated by the voltmeter. The deviation must not
exceed 1% of the set operating value.
Furthermore, gradually decrease (increase) the volt-
ages until the relay resets, i.e. the voltage alarm output
relay is disengaged. Check that the dropout to pickup
ratio is greater than 0.97 (for overvoltage function) or
smaller than 1.03 (for undervoltage).
6.4.5 Checking the relay operating time
of the over/undervoltage functions
To check the relay's operating time, a timer must be
connected to the trip outpnut relay contact (Contact
terminals D1/E1). The timer should be started simulta-
neously with the voltage change from sound condition
to a faulty condition and stopped by the trip relay con-
tact. The operating time measured by timer should
have a deviation about 3% of the set value or < 20
ms.
6.4.6 Checking the external blocking
and reset functions
The external blocking input blocks the selected voltage
functions.
Care must be taken that these terminals are also as-
signed the blocking function (refer to chapter 5.9.1).
The external blocking input inhibits undervoltage func-
tions. To test the blocking function apply auxiliary sup-
ply voltage to the external blocking input of the relay
(terminals E8/D8). Inject a test voltage which could
cause tripping for the functions above mentioned. Ob-
serve that there is no trip and alarm.
Remove the auxiliary supply voltage from the blocking
input. Apply test voltages to trip the relay (message
„TRIP“ on the display). Return the test voltages to the
sound condition and apply auxiliary supply voltage to
the external reset input of the relay (terminals C8/D8).
The display and LED indications should be reset im-
mediately.

20 TB MRU3-1 12.00 E
6.5 Primary test
Generally, a primary injection test could be carried out
in the similar manner as the secondary injection test
described above. With the difference that the pro-
tected power system should be, in this case, con-
nected to the installed relays under test „on line“, and
the test voltages should be injected to the relay through
the voltage transformers with the primary side ener-
gized. Since the cost and potential hazards are very
high for such a test, primary injection tests are usually
limited to very important protective relays in the power
system.
Because of its powerful combined indicating and
measuring functions, the MRU1 relay may be tested in
the manner of a primary injection test without extra ex-
penditure and time consumption.
In actual service, for example, the measured voltage
values on the MRU3-1 relay display may be com-
pared phase by phase with the concerned indications
of the instruments of the switchboard to verify that the
relay works and measures correctly.
6.6 Maintenance
Maintenance testing is generally done on site at regu-
lar intervals. These intervals vary among users depend-
ing on many factors: e.g. the type of protective relays
employed; the importance of the primary equipment
being protected; the user's past experience with the re-
lay, etc.
For electromechanical or static relays, maintenance
testing will be performed at least once a year accord-
ing to the experiences. For digital relays like MRU3-1,
this interval can be substantially longer. This is be-
cause:
•the MR- relays are equipped with very wide self-
supervision functions, so that many faults in the relay
can be detected and signalised during service. Im-
portant: The self-supervision output relay must be
connected to a central alarm panel!
•the combined measuring functions of MR-relays en-
able supervision the relay functions during service.
•the combined TRIP test function of the MR-relay al-
lows to test the relay output circuits.
A testing interval of two years for maintenance will,
therefore, be recommended.
During a maintenance test, the relay functions includ-
ing the operating values and relay tripping times
should be tested.