Seg MRN3 User manual

MRN3 -Mains decoupling relay

2TB MRN3 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
3.2 Parameter settings
3.3 LEDs
3.4 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 Principle of frequency supervision
4.5 Measuring of frequency gradient (MRN3-2)
4.6 Vector surge supervision (MRN3-1)
4.6.1 Measuring principle of vector surge
supervision
4.7 Voltage threshold value for frequency
measuring
4.8 Blocking function
5 Operation and setting
5.1 Display
5.2 Setting procedure
5.3 Systemparameter
5.3.1 Display of residual voltage UE as 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
(FLSH/NOFL)
5.3.5 Parameterswitch/external trigger for the
fault recorder
5.4 Protection parameters
5.4.1 Parameter setting of over- and under-
voltage supervision
5.4.2 Number of measuring repetitions (T) for
frequency functions
5.4.3 Threshold of frequency supervision
5.4.4 Tripping delays for the frequency elements
5.4.5 Parameter setting of vector surge
supervision (MRN3-1)
5.4.6 Parameter setting of frequency gradient
(MRN3-2)
5.4.7 Voltage threshold value for frequency
and vector surge measuring (df/dt at
MRN3-2)
5.4.8 Adjustment of the slave address
5.4.9 Setting of Baud-rate (applies for Modbus
Protocol only)
5.4.10 Setting of parity (applies for Modbus
Protocol only)
5.5 Adjustment of the fault recorder
5.5.1 Number of the fault recordings
5.5.2 Adjustment of trigger occurences
5.5.3 Pre-trigger time (Tpre)
5.6 Adjustment of the clock
5.7 Additional functions
5.7.1 Setting procedure for blocking the
protection functions
5.8 Indication of measuring values
5.8.1 Measuring indication
5.8.2 Min./Max.- values
5.8.3 Unit of the measuring values displayed
5.8.4 Indication of fault data
5.9 Fault memory
5.9.1 Reset
5.9.2 Erasure of fault storage

TB MRN3 12.00 E 3
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
6.5 Example of test circuit
6.5.1 Checking the input circuits and
measuring functions
6.5.2 Checking the operating and resetting
values of the over/undervoltage functions
6.5.3 Checking the relay operating time of the
over/undervoltage functions
6.5.4 Checking the operating and resetting
values of the over/underfrequency
functions
6.5.5 Checking the relay operating time of the
over/underfrequency functions
6.5.6 Checking the vector surge function
6.5.7 Checking the external blocking and reset
functions
6.6 Primary injection test
6.7 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 Parameters for the fault recorder
7.4 Output relays
8 Order form

4TB MRN3 12.00 E
1 Introduction and application
The MRN3 is a universal mains decoupling device and
covers the protection requirements from VDEW and
most other utilities for the mains parallel operation of
power stations.
•Over/ and undervoltage protection,
•over/ and underfrequency protection,
•extremely fast decoupling of generator in case of
mains failure (MRN3-1) or
•rate of change of frequency df/dt (MRN3-2)
Because of combination of three protectional functions
in one device the MRN3 is a very compact mains de-
coupling device. Compared to the standardly used sin-
gle devices it has a very good price/performance ratio.
For applications where the single protection functions
are required SEG can offer the single MR-relays as fol-
lows:
•MRU3-1 four step independent over-/ and under-
voltage protection (also used for gene-
rator earth fault protection).
•MRU3-2 two step independent over-/ and under-
voltage protection with evaluation of the
symmetrical voltage components.
•MRF3 four step independent over/ and under-
frequency protection and two step
frequency gradient supervision df/dt.
•MRG2 generator mains monitor / vector surge
detection.
Important:
For additional common data of all MR-relays please re-
fer to technical description "MR - Digital Multifunctional
Relays".
2 Features and characteristics
•Microprocessor technology with watchdog,
•effective analog low pass filter for suppressing har-
monics when measuring frequency and vector surge,
•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 op-
erations,
•integrated functions for voltage, frequency and vector
surge in one device as well as single voltage, fre-
quency and vector surge devices,
•two parameter sets,
•voltage supervision each with two step under-/ and
overvoltage detection,
•frequency supervision with three step under-/ or over-
frequency (user setting),
•completely independent time settings for voltage and
frequency supervision,
•adjustable voltage threshold value for blocking fre-
quency and vector surge measuring,
•display of all measuring values and setting parameters
for normal operation as well as tripping via a alpha-
numerical display and LEDs,
•display of measuring values as primary quantities
•Storage of trip values and switching-off time (tCBFP) of 5
fault occurences (fail-safe of voltage),
•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,
•user configurable vector surge measurement 1-of-3 or
3-of-3,
•reliable vector surge measuring by exact calculation
algorithm,
•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 Protocol
or Modbus Protocol.

TB MRN3 12.00 E 5
3 Design
3.1 Connections
Figure 3.1: Connection diagram MRN3-1 and MRN3-2
3.1.1 Analog input circuits
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 measur-
ing circuits can be applied in star or delta connection
(refer to chapter 4.3.1).
3.1.2 Blocking input
The blocking function can be set according to require-
ment. By applying the auxiliary voltage to D8/E8, the
previously set relay functions are blocked (refer to 4.8
and 5.7.1).
3.1.3 Reset input
Please refer to chapter 5.9.1.
3.1.4 Output relays
The MRN3 is equipped with 5 output relays. Apart from
the relay for self-supervision, all protective functions can
be optionally assigned:
•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.

6TB MRN3 12.00 E
3.1.5 Fault recorder
The MRN3 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 influ-
enced.
No writing over
If 2, 4 or 8 recordings are chosen, the complete mem-
ory is divided into the relevant number of partial seg-
ments. If this max. number of fault event has been ex-
ceeded, 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 re-
corder 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 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).
Figure 3.2: Division of the memory into 8 segments, for example
Memory space 6 to 4 is occupied.
Memory space 5 is currently being written in
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 3.3: 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.
Via the interface RS485 the data can be read and
processed by means of a PC (HTL/PL-Soft4). The data is
graphically edited and displayed. Binary tracks are re-
corded as well, e.g. activation and trip.

TB MRN3 12.00 E 7
3.2 Parameter settings
System parameters
Parameter settings MRN3-1 MRN3-2
Uprim/Usek XX
∆/Y XX
fN X X
P2/FR X X
LED-Flash X X
Table 3.1: System parameters
Protection parameters
Setting
parameter
MRN3-1 MRN3-2
U< X X
tU< XX
U<< X X
tU<< XX
U> X X
tU> XX
U>> X X
tU>> XX
TXX
f1XX
tf1 XX
f2XX
tf2 XX
f3XX
tf3 XX
df X
dt X
1/3 X
∆Θ X
UB<XX
RS485/Slave X X
Baud-Rate* X X
Parity-Check* X X
Table 3.2: Protection parameters
*only Modbus
Blocking functions
Parameter settings MRN3-1 MRN3-2
U< X X
U<< X X
U> X X
U>> X X
f1 X X
f2 X X
f3 X X
∆θX
df/dt X
Table 3.3: Blocking functions
Parameters for the fault recorder
Parameter setting MRN3-1 MRN3-2
Number of fault
events
XX
Trigger events X X
Pre-Triggerzeit Tpre XX
Table 3.4: Parameters for the fault recorder
Additional functions
Parameter settings MRN3-1 MRN3-2
Ralay assignment X X
Fault recorder X X
Table 3.5: Additional functions
Date and time
Parameter settings MRN3-1 MRN3-2
Year Y = 99
Month M = 03
Day D = 16
hour h = 07
minute m = 29
second s = 56
X
X
X
X
X
X
X
X
X
X
X
X
Table 3.6: Date and time
The window for parameter setting is located behind the
measured value display. The parameter window can be
accessed via the <SELECT/RESET> key.

8TB MRN3 12.00 E
3.3 LEDs
All LEDs (except LED RS, min. and max.) are two-
coloured. The LEDs on the left side, next to the alpha-
numerical 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 set-
ting 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 communi-
cation.
The LED marked with the letters FR is alight while the
fault recorder is being adjusted.
3.4 Front plate
Figure 3.4: Front plate MRN3-1
Figure 3.5: Front plate MRN3-2

TB MRN3 12.00 E 9
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 measur-
ing quantity, at 50 Hz.
4.2 Digital circuits
The essential part of the MRN3 relay is a powerful mi-
crocontroller. All of the operations, from the analog digi-
tal conversion to the relay trip decision, are carried out
by the microcontroller digitally. The relay program is lo-
cated in an EPROM (Electrically-Programmable-Read-
Only-Memory). With this program the CPU of the mi-
crocontroller calculates the three phase voltage in order
to detect a possible fault situation in the protected ob-
ject.
For the calculation of the voltage value an efficient digi-
tal filter based on the Fourier Transformation (DFFT - Dis-
crete Fast Fourier Transformation) is applied to suppress
high frequency harmonics and d.c. components caused
by fault-induced transients or other system disturbances.
The microprocessor continuously compares the meas-
ured values with the preset thresholds stored in the pa-
rameter 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 element of MRN3 has the application in
protection of generators, consumers and other electrical
equipment against over-/and undervoltage.
The relay is equipped with a two step independent
three-phase overvoltage (U>, U>>) and undervoltage
(U<, U<<) function with completely separate time and
voltage settings.
In delta connection the phase-to-phase voltages and in
star connection the phase-to-neutral voltages are con-
tinuously compared with the preset thresholds.
For the overvoltage supervision the highest, for the un-
dervoltage supervision of the lowest voltage of the three
phases are decisive for energizing.

10 TB MRN3 12.00 E
4.3.1 Selection of star or delta
connection
All connections of the input voltage transformers are led
to screw terminals. The nominal voltage of the device is
equal to the nominal voltage of the input transformers.
Dependent on the application 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 reduced by
1/ 3 . During parameter setting the connection con-
figuration either Y or ∆has to be adjusted.
)!
)"
)#
)$
)%
)&
7
7 !
7!
Sec. winding of
mains V.T.
=
>
?
Figure 4.1: Input v.t.s in delta connection (
∆
)
)!
)"
)#
)$
)%
)&
7
7
7!
Sec. winding of
mains V.T.
=
>
?
Figure 4.2: Input v.t.s in star connection (Y)
4.4 Principle of frequency supervision
The frequency element of MRN3 protects electrical
generators, consumers or electrical operating equipment
in general against over- or underfrequency.
The relay has independent three frequency elements
f1- f3with a free choice of parameters, with separate
adjustable pickup values and delay times.
The measuring principle of the frequency supervision is
based in general on the time measurement of complete
cycles, whereby a new measurement is started at each
voltage zero passage. The influence of harmonics on
the measuring result is thus minimized.
J
KJ 6
6
Figure 4.3: Determination of cycle duration by means of zero
passages.
In order to avoid false tripping during occurence of in-
terference voltages and phase shifts the relay works with
an adjustable measuring repetition. (refer to chapter
5.4.2)
Frequency tripping is sometimes not desired by low
measured voltages which for instance occur during al-
ternator acceleration. All frequency supervision functions
can be blocked with the aid of an adjustable voltage
threshold UBin case the measured voltages value is be-
low this value.
4.5 Measuring of frequency gradient
(MRN3-2)
Electrical generators running in parallel with the mains,
e.g. industrial internal power supply plants, should be
separated from the mains when failure in the intrasystem
occurs for the following reasons:
•It must be prevented that the electrical generators are
damaged when mains voltage recovering asyn-
chrone, e.g. after a short interruption.
•The industrial internal power supply must be main-
tained.

TB MRN3 12.00 E 11
A reliable criterion of detecting mains failure is the
measurement of the rate of change of frequency df/dt.
Precondition for this is a load flow via the mains cou-
pling point. At mains failure the load flow changing
then spontaneously leads to an increasing or decreasing
frequency. At active power deficit of the internal power
station a linear drop of the frequency occurs and a lin-
ear increase occurs at power excess. Typical frequency
gradients during application of "mains decoupling" are
in the range of 0.5 Hz/s up to over 2 Hz/s. The
MRN3 detects the instantaneous frequency gradient
df/dt of each mains voltage period in an interval of one
half period each. Through multiple evaluation of the fre-
quency gradient in sequence the continuity of the direc-
tional change (sign of the frequency gradient) is deter-
mined. Because of this special measuring procedure a
high safety in tripping and thus a high stabilty against
transient processes, e.g. switching procedure are
reached. The total switching off time at mains failure is
between 60 ms and 80 ms depending on the setting.
4.6 Vector surge supervision (MRN3-1)
The vector surge supervision protects synchronous gen-
erators in mains parallel operation due to very fast de-
coupling in case of mains failure. Very dangerous are
mains auto reclosings for synchronous generators. The
mains voltage returning after 300 ms can hit the gen-
erator in asynchronous position. A very fast decoupling
is also necessary in case of long time mains failures.
Generally there are two different applications:
a) Only mains parallel operation no single opera-
tion:
In this application the vector surge supervi- sion
protects the generator by tripping the genera- tor
circuit breaker in case of mains failure.
b) Mains parallel operation and single operation:
For this application the vector surge supervision
trips the mains circuit breaker. Here it is insured
that the gen.-set is not blocked when it is required
as the emergency set.
A very fast decoupling in case of mains failures for syn-
chronous generators is known as very difficult. Voltage
supervision units cannot be used because the synchro-
nous alternator as well as the consumer impedance
support the decreasing voltage.
For this the mains voltage drops only after some
100 ms below the pickup threshold of voltage supervi-
sion relays and therefore a safe detection of mains auto
reclosings is not possible with this kind of relay.
Frequency relays are partial unsuitable because only a
highly loaded generator decreases its speed within 100
ms. Current relays detect a fault only when short-circuit
type currents exist, but cannot avoid their development.
Power relays are able to pickup within 200 ms, but they
cannot prevent power to rise to short-circuit values too.
Since power changes are also caused by sudden
loaded alternators, the use of power relays can be
problematic.
Whereas the MRN3-1 detects mains failures within
60 ms without the restrictions described above because
they are specially designed for applications where very
fast decoupling from the mains is required.
Adding the operating time of a circuit breaker or con-
tactor, the total disconnection time remains below
150 ms. Basic requirement for tripping of the genera-
tor/mains monitor is a change in load of more than 15
- 20% of the rated load. Slow changes of the system
frequency, for instance at regulating processes (adjust-
ment of speed regulator) do not cause the relay to trip.
Trippings can also be caused by short-circuits within the
grid, because a voltage vector surge higher than the
preset value can occur. The magnitude of the voltage
vector surge depends on the distance between the short-
circuit and the generator. This function is also of advan-
tage to the Power Utility Company because the mains
short-circuit capacity and consequently the energy feed-
ing the short-circuit is limited.
To prevent a possible false tripping the vector surge
measuring can be blocked at a set low input voltage
(refer to 5.4.7). The undervoltage lockout acts faster
then the vector surge measurement.
Vector surge tripping is blocked by a phase loss so that
a VT fault (e.g. faulty VTs fuse) does not cause false
tripping.
When switching on the aux. voltage or measuring volt-
age , the vector surge supervision is blocked for 5 s (re-
fer to chapter 4.8).

12 TB MRN3 12.00 E
Note:
In order to avoid any adverse interference voltage ef-
fects, for instance from contactors or relays, which may
cause overfunctions, MRN3-1 should be connected
separately to the busbar.
4.6.1 Measuring principle of vector
surge supervision
When a synchronous generator is loaded, a rotor dis-
placement angle is build between the terminal voltage
(mains voltage U1) and the synchronous internal voltage
(Up). Therefore a voltage is difference ∆U is built be-
tween Up and U1 (Fig. 4.4).
~
∆
U = I jX@I
I
U2UMains
Z
Figure 4.4: Equivalent circuit at synchronous generator in parallel
with the mains
Figure 4.5: Voltage vectors at mains parallel operation
The rotor displacement angle ϑbetween stator and
rotor is depending of the mechanical moving torque
of the generator shaft. The mechanical shaft power is
balanced with the electrical feeded mains power, and
therefore the synchronous speed keeps constant
(Fig. 4.5).
~
∆
U' = I' jX@I'
U2U'Mains
Z
Figure 4.6: Equivalent circuit at mains failure
In case of mains failure or auto reclosing the generator
suddenly feeds a very high consumer load. The rotor
displacement angle is decreased repeatedly and the
voltage vector U1changes its direction (U1') (Fig. 4.6
and 4.7).
Figure 4.7: Voltage vectors at mains failure

TB MRN3 12.00 E 13
Figure 4.8: Voltage vector surge
As shown in the voltage/time diagram the instantane-
ous value of the voltage jumps to another value and the
phase position changes. This is named phase or vector
surge.
The MRN3-1 measures the cycle duration. A new
measuring is started at each voltage zero passage. The
measured cycle duration is internally compared with a
quartz stable reference time and from this the deviation
of the cycle duration of the voltage signal is ascer-
tained. In case of a vector surge as shown in fig. 4.8,
the zero passage occurs either earlier or later. The es-
tablished deviation of the cycle duration is in compli-
ance with the vector surge angle.
If the vector surge angle exceeds the set value, the relay
trips immediately.
Tripping of the vector surge is blocked in case of loss of
one or more phases of the measuring voltage.
Tripping logic for vector surge measurement:
The vector surge function of the MRN3-1 supervises vec-
tor surges in all three phases at the same time. Tripping
of the relay can be adjusted for an one phase vector
surge (more sensitive measurement). For this the parame-
ter 1/3 has to be set to "1Ph". When the parameter
1/3 is set to "3Ph", tripping of the vector surge element
occurs only if the vector surge angle exceeds the set
value in all three phases at the same time.

14 TB MRN3 12.00 E
Application hint
Although the vector surge relay guarantees very fast and
reliable detection of mains failures under nearly all op-
erational conditions of mains parallel running alterna-
tors, the following borderline cases have to be consid-
ered accordingly:
a) None or only insignificant change of power flow at
the utility connection point during mains failures.
This can occure during peak lopping operation or in
CHP stations (Combined Heat and Power) where the
power flow between power station and the public grid
may be very low. For detection of a vector surge at
parallel running alternators, the load change must be at
least 15 - 20% of the rated power. If the active load at
the utility connection point is regulated to a minimal
value and a high resistance mains failure occurs, then
there are no vector surge nor power and frequency
changes and the mains failure is not detected.
This can only happen if the public grid is disconnected
near the power station and so the alternators are not
additionally loaded by any consumers. At distant mains
failures the synchronous alternators are abruptly loaded
by remaining consumers which leads directly to a vector
surge and so mains failure detection is guaranteed.
If such a situation occurs the following has to be taken
into account:
In case of an undetected mains failure, i.e. with the
mains coupling C.B. closed, the vector surge relay re-
acts upon the first load change causing a vector surge
and trips the mains C.B.
For detecting high resistance mains failures a minimum
current relay with an adjustable trip delay can be used.
A trip delay is needed to allow regulating actions
where the current may reach "zero" at the utility connec-
tion point. At high resistance mains failures, the mains
coupling C.B. is tripped by the minimum current relay
after the time delay.
To prevent asynchronous switching on, an automatic re-
closing of the public grid should be not possible during
this time delay.
A further measure could be, that the load regulation at
the utility connection point guarantees a minimum power
flow of 15 - 20% of rated power.
b) Short circuit type loading of the alternators at distant
mains failures
At any distant mains failure, the remaining consumers
cause sudden short circuit type loading of the power
station generators. The vector surge relay detects the
mains failure in about 60 ms and switches off the mains
coupling C.B. The total switch off time is about 100 -
150 ms. If the generators are provided with an ex-
tremely fast short circuit protection e.g. able to detect
di/dt, the alternators might be switched off unselectively
by the generator C.B., which is not desireable because
the power supply for the station is endangered and later
on synchronized changeover to the mains is only possi-
ble after manual reset of the overcurrent protection.
To avoid such a situation, the alternator C.B.s must have
a delayed short circuit protection. The time delay must
be long enough so that mains decoupling by the vector
surge relay is guaranteed.

TB MRN3 12.00 E 15
4.7 Voltage threshold value for
frequency measuring
At low measuring voltages, e.g. during generator start-
up, frequency and vector surge or df/dt-measuring is
perhaps not desired.
By means of the adjustable voltage threshold value UB<,
functions f1- f3, df/dt or ∆Θ are blocked if the measured
voltage falls below the set value.
4.8 Blocking function
No. Dynamic Behaviour U</<< U>/>> f1, f2, f3∆Θ df/dt
1 voltage to external
blocking input is
applied
free program-
mable
free program-
mable
free program-
mable
free program-
mable
free program-
mable
2 blocking input is
released
released
instantaneously
released
instantaneously
released after
1 s
released after
5 s
released after
5 s
3 supply voltage is
switched on
blocked for
200 ms
blocked for
200 ms
blocked for 1 s blocked for 1 s blocked for 1 s
4 3ph measuring volt.
is suddenly applied
released released blocked for 1 s blocked for 5 s blocked for 5 s
5 one or several
measuring voltages
are switched off
suddenly (phase
failure)
released released blocked blocked blocked
6measuringvoltage
smaller UB< (adjust-
able voltage thresh-
old value)
released released blocked blocked blocked
Table 4.1: Dynamic behaviour of MRN3 functions
Blocking function set in compliance with require-
ments:
The MRN3 has an external blocking input. By applying
the auxiliary voltage to input D8/E8, the requested pro-
tection functions of the relay are blocked (refer to
5.7.1).

16 TB MRN3 12.00 E
5 Operation and setting
5.1 Display
Function Display shows Pressed pushbutton Corresponding
LED
Type of
relay
Normal operation SEG all types
Measured operating values Actual measured value
Min. and max. values
of voltage, frequency
and vector surge
<SELECT/RESET> one
time for each value
L1, L2, L3,
f, min, max
∆Θ
df
MRN3-1
MRN3-2
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. Trigger for
FR
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><+><->
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
frequency measuring repitition setting value <SELECT/RESET><+><-> T
frequency element f1
tripping delay of frequency element f1
setting value in Hz
setting value in seconds
<SELECT/RESET><+><->
one time for each value
f1
tf1
frequency element f2
tripping delay of frequency element f2
setting value in Hz
setting value in seconds
<SELECT/RESET><+><->
one time for each value
f2
tf2
frequency element f3
tripping delay of frequency element f3
setting value in Hz
setting value in seconds
<SELECT/RESET><+><->
one time for each value
f3
tf3
1-of-3/3-of-3 measurement 1Ph/3Ph <SELECT/RESET><+><-> 1/3 MRN3-1
threshold for vector surge setting value in degree <SELECT/RESET><+><-> ∆Θ MRN3-1
setting value df/dt
measuring repitition df/dt
setting value in Hz/s
setting value in periods
<SELECT/RESET><+><->
one time for each value
df
dt
MRN3-2
Blocking EXIT <+> until max. setting
value
LED of blocked
parameter
Undervoltage blocking of
frequency and vector surge meas-
uring (df/dt for MRN3-2)
setting value in Volt <SELECT/RESET><+><-> f, ∆Θ, df
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>>
frequency tripping values in Hz <SELECT/RESET><+><->
one time for each phase
f, f1, f2, f3
rate of change of frequency tripping value in Hz/s <SELECT/RESET><+><-> df MRN3-2
vector surge tripping value in degree <SELECT/RESET><+><->
one time for each phase ∆Θ + L1, L2 or L3 MRN3-1
Delete failure memory wait <-> <SELECT/RESET>
1) only Modbus

TB MRN3 12.00 E 17
Function Display shows Pressed pushbutton Corresponding
LED
Type of
relay
Enquiry failure memory FLT1; FLT2..... <-><+> L1, L2, L3, U<,
U<<, U>, U>>, f,
Ddf/dt, ∆Θ
Save parameter? SAV? <ENTER>
Save parameter! SAV! <ENTER> for about 3 s
Trigger signal for the fault re-
corder
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
Table 5.1: Possible indication messages on the display

18 TB MRN3 12.00 E
5.2 Setting procedure
In this paragraph the settings for all relay parameters
are described in detail. For parameter setting a pass-
word has to be entered first (please refer to 4.4 of de-
scription "MR-Digital Multifunctional Relays").
5.3 Systemparameter
5.3.1 Display of residual voltage UE
as 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 "sek", the measuring value is shown as rated secon-
dary 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 ∆
∆∆
∆/Y – Switch over
Depending on the mains voltage conditions, the input
voltage transformers can be operated in delta or Y con-
nection. Change-overs are effected via the <+> and the
<-> keys and stored with <ENTER>.

TB MRN3 12.00 E 19
5.3.3 Setting of nominal frequency
For proper functioning it is necessary to first adjust the
rated frequency (50 oder 60 Hz).
For this a distinction has to be made between the set-
tings v = 50 Hz / f = 50 Hz or v = 60 Hz /
f = 60 Hz
The difference lies in the method of voltage measuring.
With the setting "v“ = 50/60 Hz voltage measuring is
independent of the existing frequency. This means, the
voltage value can be correctly measured between 30
Hz and 80 Hz without adverse effects from the fre-
quency.
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.
The different designations "f“ or "v“ have no influence on
any of the other functions.
All frequency functions are determined by setting the
nominal frequency, i.e. whether the set frequency
thresholds are evaluated as over- or underfrequency (see
also chapter 5.4.4). Also the cycle duration
(20 ms at 50 Hz and 16.67 ms at 60 Hz) derives from
this setting which determines the minimum tripping delay
for frequency elements f1- f3with an adjustable multiplier
(see also chapter 5.4.5).
During setting of the nominal frequency a value in Hz is
shown on the display.
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 5.2)
none 0.5..1%/Hz (see
table 5.2)
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 or 60 Hz
* Setting is important for differentiation between over- and underfrequency
** 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.

20 TB MRN3 12.00 E
5.3.4 Display of the activation storage
(FLSH/NOFL)
If after an activation the existing current drops again be-
low 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 sup-
pressed when the parameter is set to NOFL.
5.3.5 Parameterswitch/external trigger
for the fault recorder
By means of the parameter-change-over switches it is
possible to activate two different parameter sets. Switch-
ing 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 inputs can be
used for Reset or blocking and for 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 trig-
gerung of the
fault recorder
S2_FR Parameter switch External trig-
gerung of the
fault recorder
With the settings SET1 or SET2 the parameter set is ac-
tivated 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 set-
ting R_S2 the reset input (D8, E8) is used as parameter-
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 setting R_FR the
fault recorder is activated via the reset input. With the
setting S2_FR parameter set 2 can be activated via the
blocking input and/or the fault recorder via the reset in-
put. The relevant function is then activated by applying
the auxiliary voltage to one of the external inputs.
With the setting R_FR the fault recorder is activated via
the reset input. With the setting S2_FR parameter set 2
can be activated 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 blocking
separately (refer to chapter 5.7.1).