Seg HighTECH Line MRN3-3 User manual

MRN3-3
PROTECTION TECHNOLOGY
MADE SIMPLE
MAINS DECOUPLING RELAY WITH DF/DT AND
PROGRAMMABLE UNDERVOLTAGE CHARACTERISTICS
HighTECH Line
MAINS DECOUPLING RELAY WITH DF/DT
AND PROGRAMMABLE UNDERVOLTAGE CHARACTERISTICS
Original document
English
Revision: A
MANUAL

2 TD_MRN3-3_08.06_GB
Contents
1 Introduction and Application
2 Features and Characteristics
3 Design
3.1 Connections
3.1.1 Analogue input circuits
3.1.2 Blocking input
3.1.3 External reset input
3.1.4 Output relays
3.1.5 Fault recorder
3.2 Order of parameter settings
3.2.1 System parameters
3.2.2 Protection parameters
3.2.3 Parameter related to the fault recorder
3.3 LEDs
3.4 Front plate
4 Working Principle
4.1 Analogue 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
4.6 Vector surge supervision
4.7 Measuring principle of vector surge
supervision
4.7.1 Voltage threshold value for frequency-
df/dt measuring
4.8 Blocking function
5 Operation and Settings
5.1 Display
5.2 Setting procedure
5.3 System parameters
5.3.1 Display of measuring voltages U
E
as
primary quantity (U
prim
/U
sec
)
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 Parameter change-over switch/external
triggering of the fault recorder
5.4 Protection parameter
5.4.1 Setting parameters for under voltage
characteristics
5.4.2 SYMmetrical, ASYMmetrical or GENEral
faults*
5.4.3 Permissible release time for the under
voltage characteristic curve
5.4.4 Plausibility check of the voltage
characteristic
5.4.5 Parameter setting of the voltage functions
5.4.6 Number of measuring repetitions (T) for
frequency functions
5.4.7 Threshold of the frequency supervision
5.4.8 Tripping delays for the frequency
elements
5.4.9 Parameter setting of the vector surge
supervision or the frequency rate of
change df/dt
5.4.10 Voltage threshold value for frequency
and vector surge measuring (df/dt)
5.4.11 Adjustment of the slave address
5.4.12 Setting of Baud-rate (applies for Modbus
Protocol only)
5.4.13 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 (T
pre
)
5.6 Adjustment of the clock
5.7 Additional functions
5.7.1 Setting procedure for blocking of the
protection functions and assignment of
output relays
5.8 Indication of measuring and fault 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
5.9.3 Erasure of disturbance recorder

TD_MRN3-3_08.06_GB 3
6 Relay Testing and Commissioning
6.1 Power-On
6.2 Testing the output relays and LEDs
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 values
6.5.2 Checking the operating and resetting
values at over-/undervoltage
6.5.3 Checking the tripping delay of the
over-/undervoltage functions
6.5.4 Checking the operating and resetting
values of the over-/underfrequency
functions
6.5.5 Checking the tripping delay of the
over-/underfrequency functions
6.5.6 Checking the vector surge function
6.5.7 Checking the tripping and reset values of
the df/dt stages
6.5.8 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 System parameter
7.3.2 Protection Parameter
7.3.3 Interface parameter
7.3.4 Parameters for the fault recorder
7.4 Output relays
8 Order form

4 TD_MRN3-3_08.06_GB
1 Introduction and Application
The mains decoupling relay MRN3-3 has been de-
signed for the use under special conditions, especially
to be found at wind parks.
If power generating systems are due to comply with
the GridCodes, i.e. if they shall not immediately dis-
connect from the grid in case of a mains failure, but
support it, instead, the MRN3-3 will be the optimal re-
lay. Its' function is to supervise mains voltage and
mains frequency in compliance with the GridCodes,
the grid connection rules and the operator guidelines.
For this reason, the distinction between short-distance
or long-distance errors is an elementary fact. As per
the requirements of the e-on grid connection rules (ver-
sion dd. 20.08.03) and the VDN guideline “EEG
power generating plants at high and maximum volt-
age systems”, in addition to the standard protection
functions, the MRN3-3 provides the voltage time
characteristics which are necessary to distinguish be-
tween short distance and long distance errors. Normal
voltage collapse shapes at mains failures are taken
into account by these characteristics, that allow selec-
tive disconnection of systems only there, where it is
absolutely required for operation.
If, in the event of a failure, the systems are to be con-
nected to the grid for a longer period, they will sup-
port the mains voltage and thus avoid large-area
breakdowns that could no more be compensated by
the interconnected network's primary control reserve.
Thanks to the presence of two independent character-
istics, it is possible to distinguish between short-term or
permanent interruption, each according to the type of
error.
In the event of a failure, the fault sequence can be re-
corded by an oscilloscope.
Within this error scenario, the MRN3-3 with its char-
acteristics hat have been applied for the first time in
protection technique - is of enormous use for the accu-
rate identification and analysis of the grid state - as
demanded by the rules.
General Note:
For further technical data and detailed descriptions,
please refer to our "MR - Digital Multifunctional Re-
lays".
2 Features and Characteristics
• Microprocessor technology with watchdog,
• effective analogue low pass filter for suppressing
harmonics 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
operations,
• integrated functions for voltage, frequency and vec-
tor surge df/dt supervision in one device,
• two parameter sets,
• two free programmable under voltage limit curves
with each 5 definition points,
• three voltage supervision steps with under or over
voltage function that can be freely parameterised,
• frequency supervision with three step under-/or
over frequency function (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 parame-
ters for normal operation as well as tripping via a
alphanumerical display and LEDs,
• display of measuring values as primary quantities
• Storage of the pickup- and tripping values of three
failure events (voltage fail-safe),
• recording of up to four fault occurences with time
stamp
• to block the individual functions by the external
blocking input, parameters can be set according to
requirement,
• reliable vector surge measuring by exact calculation
algorithm,
• suppression of indication after an activation
(LED flash),
• Direct connection 690 V (linked).
• 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.

TD_MRN3-3_08.06_GB 5
3 Design
3.1 Connections
Figure 3.1: Connection diagram MRN3-3
3.1.1 Analogue input circuits
The analogue input voltages are galvanically decoup-
led by the input transformers of the device, then filtered
and finally fed to the analogue digital converter. The
measuring circuits can be applied in star or delta con-
nection (refer to chapter 4.3.1).
3.1.2 Blocking input
The blocking function can be set according to re-
quirement. 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 MRN3-3 is equipped with 5 output relays. Apart
from the relay for self-supervision, all protective func-
tions 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.

6 TD_MRN3-3_08.06_GB
3.1.5 Fault recorder
The MRN3-3 has a fault value recorder which records
the measured analogue values as instantaneous val-
ues.
The instantaneous values
U
L1
; U
L2
; U
L3
for star connection
or U
12
; U
23
; U
21
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 occurrences with a total
recording time of 18 s (with 50 Hz) and 15 s (with
60 Hz) per channel.
Storage division
Independent of the recording time, the entire storage
capacity can be divided into several of disturbance
events 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 re-
cordings in order to prevent that the stored data are
written over. After the data have been read and de-
leted, the recorder is 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.
Thus, the fault recorder can be adjusted to record the
following data/parameters:
Recorded length of time
Number of re-
corded faults 50 Hz 60Hz
1* 20 s 16.66 s
1 10 8.33 s
2* 10 s 8.33 s
3 5 s 4.16 s
4* 5 s 4.16 s
7 2.5 s 2.08 s
8* 2.5 s 2.08 s
When there is no more storage capacity left, the LED
FR starts flashing.
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, for example, 8 segments
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.
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
recorded as well, e.g. activation and trip.

TD_MRN3-3_08.06_GB 7
3.2 Order of parameter settings
3.2.1 System parameters
Setting parameter Unit Range
L1, L2, L3
Transmission ratio of the voltage transformers SEK, 1.01...6500
∆/Y
Input voltage correction depending on the input voltage
transformer connection
Y = star
DELT = Delta
fN
Adjustment of the rated frequency
Hz
50/60
∆Θ/df
Selection vector surge or df/dt function dPhi/dfdt
LED flashing after excitation
FLSH
FLSH/NOFL = flashing
NOFL = no flashing
P2
Parameter set change-over switch/Assignment of digital
inputs
Set1 = parameter set 1
Set2/2 = parameter set 2
FR = External triggering
B = External blocking
R = External Reset
SET 1
SET2
B_S2
R_S2
B_FR
R_FR
S2_FR
(refer to chapter 5.3.5)
3.2.2 Protection parameters
Setting parameters Unit Range
Char1+U<Start Start point of the limit curve 1 V 1–200/1–460/4–800*
Char1
Symmetrical, asymmetrical or general fault SYM; ASYM, ALL
Char1 Under voltage limit curve 1 warn = Display shows no „TRIP“
trip = Display shows „TRIP“
Char1+U<1 1. Char. point_value 1 (voltage value) V 1* - <= U<Start
2* - <= U<Start
Char1+U<1+t> 1. Char. point_value 2 (not parameterisable) s 0s fixed
Char1+U<2 2. Char. point_value 1 (voltage value) V >= U<1–200*/>=U<1–
460*/
>=U<1–800*
Char1+U<2+t> 2. Char. point_value 2 (time value) s > U<1+t> - 60s
Char1+U<3 3. Char. point_value 1 (voltage value) V >= U<2–200*/
>=U<2–460*/>=U<2–800*
Char1+U<3+t> 3. Char. point_value 2 (time value) s > U<2+t> - 60s
Char1+U<4 4. Char. point_value 1 (voltage value) V >= U<3–200*/
>=U<3–460*/>=U<3–800*
Char1+U<4+t> 4. Char. point_value 2 (time value) s > U<3+t> - 60s
Char1+U<5 5. Char. point_value 1 (voltage value) V >= U<4–200* and
>= U<Start–200*/
>= U<4–460* and
>= U<Start–460*/
>=U< 4–800* and
>= U<Start–800*
Char1+U<5+t> 5. Char. point_value 2 (time value) s > U<4+t> - 60s
Char1+tR Release time after voltage recovery 1 s 0.06 – 1.00s
Char2+U<Start Start point the limit curve 2 V 1–200/1–460/4–800*
Char2 Under voltage limit curve 2 warn = Display shows no „TRIP“
trip = Display shows „TRIP“
Char2
Symmetrical, asymmetrical or general fault SYM; ASYM, ALL
Char2+U<1 1. Char. point_value 1 (voltage value) V 1* - <= U<Start
2* - <= U<Start

8 TD_MRN3-3_08.06_GB
Setting parameters Unit Range
Char2+U<1+t> 1. Char. point_value 2 (not parameterisable) s 0s fixed
Char2+U<2 2. Char. point_value 1 (voltage value) V >= U<1–200*/
>=U<1–460*/>= U<1–800*
Char2+U<2+t> 2. Char. point_value 2 (time value) s > U<1+t> - 60s
Char2+U<3 3. Char. point_value 1 (voltage value) V >= U<2–200*/
>=U<2–460*/>= U2–800*
Char2+U<3+t> 3. Char. point_value 1 (time value) V > U<2+t> - 60
Char2+U<4 4. Char. point_value 1 (voltage value) V >= U<3–200*/
>=U<3–460*/>=U3–800
Char2+U<4+t>
4. Char. point_value 2 (time value)
s
> U<3+t> - 60s
Char2+U<5
5. Char. point_value 1 (voltage value)
V
>= U<4–200* and
>= U<Start–200*/
>= U<4–460* and
>= U<Start–460*/
>= U<4–800* and
>= U<Start–800*
Char2+U<5+t>
5. Char. point_value 2 (time value)
s
> U<4+t> - 60s
Char2+tR
Release time after voltage recovery 1
s
0.06 – 1.0
U1
Function of the 1st voltage element U< = undervoltage
U> = overvoltage
U1 Pick-up value for the 1st voltage element V 1–200/1–460/4–800*
tU1 (U1+t>) Tripping time for the 1st voltage element s 0,04 - 290
U2
Function of the 2nd voltage element U< = undervoltage
U> = overvoltage
U2 Pick-up value of the 2nd voltage element V 1–200/1–460/4–800*
tU2 (U2+t>) Tripping time of the 2nd voltage element s 0.04 - 290
U3
Function of the 3rd voltage element U< = undervoltage
U> = overvoltage
U3 Pick-up value of the 3rd voltage element V 1–200/1–460/4–800*
tU3 (U3+t>) Tripping time of the 3rd voltage element s 0,04 - 290
T Frequency measuring repetition in periods periods 2 - 99
f1Pickup value for frequency element 1 Hz 30–70 or 40–80
tf1 (f1+t>) Tripping delay of the 1st frequency element s tfmin. -290
f2pickup value for frequency element 2 Hz 30–70 or 40–80
tf2 (f2+t>) Tripping delay of the 2nd frequency element s tfmin -290
f3Pick-up value for frequency element 2 Hz 30–70 or 40–80
tf3 (f3+t>) Tripping delay of the 3rd frequency element s tfmin -290
∆Θ Pick-up value for the vector surge function 2–22
1-3 Vector surge tripping logic 1Pha/3Pha
df pickup value for rate of change of frequency (dt/dt) in Hz/s 0.2 - 10
dt measuring repetition for df/dt periods 2 - 64
UBvoltage threshold value for frequency and df/dt element V 5-100/12—230/20–400
RS Slave address of the serial interface 1 - 32
RS **Baud-Rate of the serial interface 1200 - 9600
RS **Parity check* even/odd/no
* Dependent on the rated voltage Un=100V/Un=230V/Un=400V/Un=690V
** Only at Modbus protocol

TD_MRN3-3_08.06_GB 9
3.2.3 Parameter related to the fault recorder
Setting parameter Unit Range
FR
Number of records 1 x 20/1 x 16.66*
1 x 10/1 x 8.33
2 x 10/2 x 8.33
3 x 5/3 x 4.11
4 x 5/4 x 4.11
7 x 2.5/7 x 2.04
8 x 2.5/8 x 2.04
FR
Storage of record, in case of event P_UP = with excitation
TRIP = with trip
A_PI = stop of all failures
TEST = test record
FR
Period before trigger event
s
0.05s – maximal recording time
*50Hz or 60Hz
Table 3.1: Parameter setting
3.3 LEDs
All LEDs (except LED FR, P2 and RS, min. and max.)
are two-coloured. The LEDs on the left side, next to the
alphanumerical display light up green during measur-
ing and red during fault message.
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 parameter-
rising 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
communication.
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 MRN3-3

10 TD_MRN3-3_08.06_GB
4 Working Principle
4.1 Analogue circuits
The input voltages are galvanically isolated by the in-
put transformers. The noise signals caused by inductive
and capacitive coupling are suppressed by an ana-
logue R-C filter circuit.
The analogue voltage signals are fed to the A/D-
converter of the microprocessor and transformed to
digital signals through Sample- and Hold- circuits. The
analogue signals are sampled with a sampling fre-
quency of 16 x f
N
, namely, a sampling rate of 1.25
ms for every measuring quantity, at 50 Hz.
4.2 Digital circuits
The essential part of the MRN3-3 relay is a powerful
microcontroller. All of the operations, from the ana-
logue 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 situa-
tion 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. compo-
nents caused by fault-induced transients or other system
disturbances. The microprocessor continuously com-
pares the measured values with the preset thresholds
stored in the parameter memory (EEPROM). If a fault
occurred an alarm is given and after the set tripping
delay has elapsed, the corresponding trip relay is ac-
tivated.
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 supervision element of MRN3-3 is used to
protect generators, consumers and other electrical
equipment from over-/and undervoltage.
The relay is equipped with a 3-step voltage supervi-
sion unit with pre-selectable under- or over voltage
function 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.

TD_MRN3-3_08.06_GB 11
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 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 ∆has to be adjusted.
A3
A4
A5
A6
A7
A8
U12
U23
U31
Sec. winding of
mains V.T.
a
b
c
Figure 4.1: Input v.t.s in delta connection ( ∆ )
A3
A4
A5
A6
A7
A8
U1
U2
U3
Sec. winding of
mains V.T.
a
b
c
Figure 4.2: Input v.t.s in star connection (Y)
4.4 Principle of frequency supervision
The frequency element of MRN3-3 protects electrical
generators, consumers or electrical operating equip-
ment in general against over- or underfrequency.
The relay has three independent frequency elements
f
1
- f
3
with individually adjustable 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 com-
plete cycles, whereby a new measurement is started at
each voltage zero passage. The influence of harmon-
ics on the measuring result is thus minimized.
t
u(t)
T
T
Figure 4.3: Determination of cycle duration by means of zero
passages.
In order to avoid false tripping during occurrence of in-
terference voltages and phase shifts the relay works
with an adjustable measuring repetition. (refer to chap-
ter 5.4.6)
Frequency tripping is sometimes not desired by low
measured voltages which for instance occur during al-
ternator acceleration. All frequency supervision func-
tions can be blocked with the aid of an adjustable
voltage threshold U
B
in case the measured voltages
value is below this value.

12 TD_MRN3-3_08.06_GB
4.5 Measuring of frequency gradient
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 intrasys-
tem occurs for the following reasons:
• It must be prevented that the electrical generators are
damaged in case of asynchronous mains voltage
recovering, e.g. after a short interruption.
• The industrial internal power supply must be main-
tained.
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 decreas-
ing frequency. At active power deficit of the internal
power station a linear drop of the frequency occurs
and a linear increase occurs at power excess. Typical
frequency gradients during application of "mains de-
coupling" are in the range of 0.5 Hz/s up to over 2
Hz/s. The MRN3-3 detects the instantaneous fre-
quency gradient df/dt of each mains voltage period
in an interval of one half period each. Through multi-
ple evaluation of the frequency gradient in sequence
the continuity of the directional change (sign of the fre-
quency gradient) is determined. Because of this spe-
cial measuring procedure a high safety in tripping and
thus a high stability 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
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
operation:
In this application the vector surge supervision
protects the generator by tripping the generator
circuit breaker in case of mains failure.
b) Mains parallel operation and isolated 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 just
required to operate as the emergency set.
A very fast decoupling in case of mains failures for
synchronous generators is known as very difficult. Volt-
age supervision units cannot be used because the syn-
chronous alternator as well as the consumer imped-
ance support the decreasing voltage.
For this reason the mains voltage drops only after
some 100 ms below the pickup threshold of voltage
supervision relays and therefore a safe detection of
mains auto reclosings is not possible with this kind of
relay.
Frequency relays, as well, are partially unsuitable be-
cause only a highly loaded generator measurably de-
creases its speed within 100 ms. Current relays detect
a fault only when short-circuit type currents exist, but
cannot avoid their development. Rate of change of
power supervision 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 rate of change of power
supervision can be problematic.
The MRN3-3 detects mains failures within 60 ms
without the restrictions described above because it
was 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 supervision unit is a change in load of at
least 15 - 20% of the rated load. Slow changes of the
system frequency, for instance at regulating processes
(adjustment 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 volt-
age vector surge depends on the distance between
the short-circuit and the generator. This function is also
of advantage to the Power Utility Company because
the mains short-circuit capacity and consequently the
energy feeding the short-circuit is limited.

TD_MRN3-3_08.06_GB 13
To prevent a possible false tripping the vector surge
measuring can be blocked at a set low input voltage
(refer to 5.4.10). 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
voltage , the vector surge supervision is blocked for 5
s (refer to chapter 4.8).
Note:
In order to avoid any adverse interference voltage ef-
fects, for instance from contactors or relays, which may
cause overfunctions, MRN3-3 should be connected
separately to the busbar.
4.7 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 volt-
age (Up). Therefore a voltage difference ∆U is built
between Up and U1 (Fig. 4.4).
~
~
∆
U = I
1
jX
d
I
2
I
1
U
P
U
1
Mai ns
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 on the mechanical moving torque
of the generator shaft. The mechanical shaft power is
balanced with the electrical fed mains power, and
therefore the synchronous speed is maintained con-
stant (Fig. 4.5).

14 TD_MRN3-3_08.06_GB
~
~
∆
U' = I
1
' jX
d
I
1
'
U
P
U
1
'
Mai ns
Z
Figure 4.6: Equivalent circuit at mains failure
In case of mains failure or auto re-closing the genera-
tor suddenly feeds a very high consumer load. The ro-
tor displacement angle suddenly increases and the
voltage vector U
1
changes its direction (U
1
') (Fig. 4.6
and 4.7).
Figure 4.7: Change of the rotor displacement angle at sudden
generator load
Figure 4.8: Voltage vector surge
As shown in the time diagram the instantaneous value
of the voltage jumps to another value and the phase
position changes. This is named phase or vector
surge.
The MRN3-3 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
ascertained. In case of a vector surge as shown in fig.
4.8, the zero passage occurs either earlier or later.
The established deviation of the cycle duration is in
compliance with the vector surge angle.
If the vector surge angle exceeds the set value, the re-
lay 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 MRN3-3 supervises
vector 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 parameter 1/3 has to be set to "1Ph". When
the parameter 1/3 is set to "3Ph", tripping of the vec-
tor surge element occurs only if the vector surge angle
exceeds the set value in all three phases at the same
time.

TD_MRN3-3_08.06_GB 15
Application hint
Although the vector surge relay guarantees very fast
and reliable detection of mains failures under nearly
all operational conditions of mains parallel running al-
ternators, the following borderline cases have to be
considered accordingly:
a) None or only insignificant change of power flow at
the utility connection point during mains failures.
This can occur 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 oc-
curs, then there are no vector surge nor power and
frequency changes and the mains failure is not de-
tected.
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 ac-
tions where the current may reach "zero" at the utility
connection 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
reclosing of the public grid should be not possible dur-
ing this time delay.
A further measure could be to design the load regula-
tion at the utility connection point as to guarantee a
minimum power flow of 15 - 20% of the generators’
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. Thus, the total switch off time is
about 100 - 150 ms. If the generators are provided
with an extremely 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 de-
sireable because the power supply for the station is
endangered and later on synchronized changeover to
the mains is only possible 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.

16 TD_MRN3-3_08.06_GB
4.8 Voltage threshold value for
frequency- df/dt measuring
At low measuring voltages, e.g. during generator start-
up, frequency or df/dt-measuring is perhaps not de-
sired.
By means of the adjustable voltage threshold value
U
B
<, functions f
1
- f
3
or df/dt are blocked if the meas-
ured voltage falls below the set value.
4.9 Blocking function
No. Dynamic
Behaviour
U</<< U>/>> f
1
, f
2
, f
3
∆Θ df/dt
1 voltage to external
blocking input is
applied
can be set acc.
to requirement
can be set
acc. to re-
quirement
can be set
acc. to re-
quirement
can be set
acc. to re-
quirement
can be set
acc. to re-
quirement
2 blocking input is
released
Instantaneously
released
released
instantane-
ously
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 5s blocked for 1
s
4 3ph measuring volt.
is suddenly applied
released released blocked for 1 s blocked for 5s blocked for 5
s
5 one or several
measuring voltages
are suddenly
switched off (phase
failure)
released released blocked blocked blocked
6 measuring voltage
smaller U
B
< (adjust-
able voltage thresh-
old value)
released released blocked blocked
Table 4.1: Dynamic behaviour of MRN3-3 functions
Blocking function set according to requirements:
The MRN3-3 has an external blocking input. By ap-
plying the auxiliary voltage to input D8/E8, the re-
quested protection functions of the relay are blocked
(refer to 5.7.1).

TD_MRN3-3_08.06_GB 17
5 Operation and Settings
5.1 Display
Function Display shows Pressed pushbutton Corresponding LED
Normal operation SEG
Measured operating values Actual measured value
Min. and max. values of
voltage, frequency and
vector surge and df/dt
<SELECT/RESET> one time
for each value
L1, L2, L3,
f, min, max
∆Θ/df
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
Selection vector surge or df/dt dPhi/dfdt <SELECT/RESET><+><-> ∆Θ/df
Parameter set change-over
switch/ext. triggering of 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><+><->
Starting point of the limit curve 1 Setting value in Volt <SELECT/RESET><+> <->
one time for each value
Char1+U<Start
Selection symmetrical, asymmetri-
cal or general fault
SYM/ASYM/ALL <SELECT/RESET><+><-> Char1
Under voltage limit curve 1
Function
warn/trip <SELECT/RESET><+><-> Char1
1. Char. point_value 1 (U<1)
1. Char. point_value_2
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+><->
set to 0s (fixed)
Char1+U<1
2. Char. point_value 1 (U<2)
2. Char. point_value_2 (tU<2)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char1+U<2
Char1+U<2+t>
3. Char. point_value 1 (U<3)
3. Char. point_value_2 (tU<3)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char1+U<3
Char1+U<3+t>
4. Char. point_value 1 (U<4)
4. Char. point_value_2 (tU<4)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char1+U<4
Char1+U<4+t>
5. Char. point_value 1 (U<5)
5. Char. point_value_2 (tU<5)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char1+U<5
Char1+U<5+t>
Permissible release time for under-
voltage limit curve 1
Setting value in seconds <SELECT/RESET><+> <->
one time for each value
Char1+tR
Starting point of the limit. curve 2 Setting value in Volt <SELECT/RESET><+><->
one time for each value
Char2+U<Start
Selection symmetrical, asymmetri-
cal or general fault
SYM/ASYM/ALL <SELECT/RESET><+><-> Char2
Under voltage limit curve 2
Function
warn/trip <SELECT/RESET><+><-> Char2
1. Char. point_value 1 (U<1)
1. Char. point_value_2
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+><->
set to 0s (fixed)
Char2+U<1
2. Char. point_value 1 (U<2)
2. Char. point_value_2 (tU<2)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char2+U<2
Char2+U<2+t>
3. Char. point_value 1 (U<3)
3. Char. point_value_2 (tU<3)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char2+U<3
Char2+U<3+t>
4. Char. point_value 1 (U<4)
4. Char. point_value_2 (tU<4)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char2+U<4
Char2+U<4+t>
5. Char. point_value 1 (U<5)
5. Char. point_value_2 (tU<5)
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
Char2+U<5
Char2+U<5+t>
Permissible release time for under-
voltage limit curve 1
Setting value in seconds <SELECT/RESET><+> <->
one time for each value
Char2+tR
Function of the 1st voltage element U</U> <SELECT/RESET><+><-> U1
Voltage threshold value U1
Tripping time delay tU1
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
U1
U1+t>
Function of the 2nd voltage element U</U> <SELECT/RESET><+><-> U2
Voltage threshold value U2
Tripping time delay tU2
Setting value in Volt
Setting value in seconds
<SELECT/RESET><+> <->
one time for each value
U2
U2+t>
Function of the 3rd voltage element U</U> <SELECT/RESET><+><-> U3

18 TD_MRN3-3_08.06_GB
Function Display shows Pressed pushbutton Corresponding LED
Voltage threshold value U1
Tripping time delay tU1
Setting value in volt
Setting value in seconds
<SELECT/RESET> <+> <->
one time for each value
U3
U3+t>
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
f1+t>
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
f2+t>
frequency element f3
tripping delay of frequency element f3
setting value in Hz
setting value in seconds
<SELECT/RESET><+><->
one time for each value
F2
f3+t>
1-OFF-3/3-OFF-3
Vector surge tripping
1Ph/3Ph <SELECT/RESET><+><-> 1-3/dt
Pick-up value for Vector surge Setting value in degree <SELECT/RESET><+><-> ∆Θ/df
df/dt pick-up value
df/dt measuring repetition
Setting value in Hz/s
Setting value in cycle
<SELECT/RESET><+><->
one time for each value
∆Θ/df
1-3/dt
Blocking EXIT <+> until max. setting value LED of blocked parameter
Blocking of a protection step via
digital input
BLOC/NO_B <SELECT/RESET><+><-> LED of the blocking
protection function
Relay assignment _ _ _ _ /
1_ _ _ 1 2 3 4
<SELECT/RESET><+><-> LED of the assigned
protective function
Voltage threshold value for the
frequency, vector surge and df/dt
measurement
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, U1, U2, U3
delta-connection:
U12, U23, U31
tripping values in Volt <SELECT/RESET><+><->
one time for each phase
L1, L2, L3, U1, U2, U3
frequency tripping values in Hz <SELECT/RESET><+><->
one time for each phase
f, f1, f2, f3, fmin,fmax
rate of change of frequency tripping value in Hz/s <SELECT/RESET><+><-> ∆Θ/df
Vector surge angle at tripping tripping value in degree <SELECT/RESET><+><-> ∆Θ + L1, L2 or L3
Enquiry failure memory FLT1; FLT2..... <-><+> L1, L2, L3, U1, U2, U3,
f1, f2, f3, ∆Θ/df
Save parameter? SAV? <ENTER>
Save parameter! SAV! <ENTER> for about 3 s
Trigger signal for the fault
recorder
TEST, P_UP, A_PI, TRIP <SELECT/RESET> <+><-> FR
Number of fault occurrences at
50 Hz
1=20; 2=10; 3=5;
4=5; 7=2; 8=2
<SELECT/RESET> <+><-> FR
Number of fault occurrences at
60 Hz
1=16; 2=8; 3=4; 4=4;
7=2; 8=2
<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

TD_MRN3-3_08.06_GB 19
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 System parameters
5.3.1 Display of residual voltage U
E
as primary quantity (U
prim
/U
sec
)
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 indicated on the dis-
play 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 ∆
∆∆
∆/Y – Switch over
Depending on the mains voltage conditions, the input
voltage transformers can be operated in delta or Y
connection. The appropriate made can be selected
via the <+> and the <-> keys and it is stored with
<ENTER>.

20 TD_MRN3-3_08.06_GB
5.3.3 Setting of nominal frequency
For proper functioning it is necessary to first adjust the
rated frequency (50 or 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 volt-
age value is influenced by the frequency (see table
5.2).
Deviation 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]
Figure 5.1: Median influence at f = 50 Hz
Deviation 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]
Figure 5.2: Median influence at f = 60 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 f
1
- f
3
with 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 figure 5.1)
none 0.5..1%/Hz
(see figure 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 Hz 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.