Woodward MRS1 User manual

MRS1 - Negative sequence relay
Manual MRS1 (Revision A)

Woodward Manual MRS1 GB
2 DOK-TD-MRS1 Rev.A
Woodward Governor Company reserves the right to update any portion of this publication at any time. Information
provided by Woodward Governor Company is believed to be correct and reliable. However, no responsibility is as-
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© Woodward 1994-2008

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 3
Contents
1.Introduction and application.......................................................................4
2.Features and characteristics ......................................................................4
3.Design...........................................................................................................5
3.1Connections ........................................................................................................................5
3.1.1Analog Inputs ..................................................................................................................5
3.1.2Output Relays..................................................................................................................5
3.1.3Blocking input ..................................................................................................................5
3.1.4External reset input .........................................................................................................5
3.2Display.................................................................................................................................6
3.3LEDs....................................................................................................................................7
4.Working principle.........................................................................................8
4.1Analog circuits .....................................................................................................................8
4.2Digital circuits ......................................................................................................................8
4.3Principle of negative sequence protection ..........................................................................9
4.3.1Measurement principle..................................................................................................10
5.Operations and settings............................................................................13
5.1Adjustable parameters ......................................................................................................13
5.2Setting procedure..............................................................................................................13
5.2.1Pickup value for negative sequence warning current (I2W) ...........................................13
5.2.2Time delay for negative sequence warning (tW)............................................................13
5.2.3Pickup value for negative sequence current (I2S).........................................................13
5.2.4Tripping characteristic (CHAR) .....................................................................................13
5.2.5Trip delay / thermal time-constant (T) ...........................................................................13
5.2.6Rated frequency............................................................................................................14
5.2.7Adjustment of the slave address ...................................................................................14
5.3Indication of measuring values and fault data...................................................................14
5.3.1Indication of measuring values......................................................................................14
5.3.2Indication of fault data ...................................................................................................14
5.4Reset .................................................................................................................................14
6.Relay testing and commissioning............................................................15
6.1Power-On ..........................................................................................................................15
6.2Testing the output relays...................................................................................................15
6.3Checking the set values ....................................................................................................15
6.4Secondary injection test ....................................................................................................16
6.4.1Test equipment..............................................................................................................16
6.4.2Example of test circuit for MRS1 relay ..........................................................................16
6.4.3Checking the input circuits and measured values.........................................................16
6.4.4Checking the operating and resetting values of the relay.............................................17
6.4.5Checking the relay operating time.................................................................................17
6.4.6Checking the extern blocking and reset functions ........................................................18
6.5Primary injection test.........................................................................................................18
6.6Maintenance......................................................................................................................18
7.Technical data............................................................................................19
7.1Measuring input circuits ....................................................................................................19
7.2Common data....................................................................................................................19
7.3Setting ranges and steps ..................................................................................................19
7.4Tripping characteristic .......................................................................................................20
7.5Output contact ratings .......................................................................................................20
8.Order form..................................................................................................21

Woodward Manual MRS1 GB
4 DOK-TD-MRS1 Rev.A
1.Introduction and application
The MRS1 relay is a negative sequence protection relay with universal application. It serves for
negative sequence protection of three-phase generators. With a large number of different tripping
characteristics and adjustment possibilities, the tripping characteristic can be made suitable for al-
most every type of generator with regard to its special thermal time-constant.
There is a choice between an independent or an inverse time tripping characteristic. In case of low
unbalanced load, a warning is given after an adjustable time delay. In case of inadmissible high
unbalanced load, the MRS1 relay trips in accordance with the set characteristic.
2.Features and characteristics
Digital filtering of the measured values by using discrete Fourier analysis to suppress the
high frequency harmonics and DC components caused by faults or system operations
Selectable protective functions between:
definite time over current protection andinverse time over current protection
Consideration of the thermal constant of the generator
Storage of trip values

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 5
3.Design
3.1 Connections
Abbildung 3.1: Connection diagram
3.1.1 Analog Inputs
The three phase currents are connected to the analog input current transformers: IL1 (B3 - B4), IL2
(B5 - B6), IL3 (B7 - B8).
The constantly detected current measuring values are galvanic ally decoupled, filtered and finally
fed to the analog / digital converter.
3.1.2 Output Relays
The MRS1 has 4 output relays, one of them with two change-over contacts is used for tripping, the
other relays with one change-over contact each are used for indication.
Tripping output relay C1, D1, E1, C2, D2, E2
Indication self-supervision C7, D7, E7
Warning for negative sequence current (I2W) C4, D4, E4
Alarm for negative sequence current pickup (I2S) C5, D5, E5
All trip and alarm relays are working current relays, the relay for self supervision is an idle current
relay
3.1.3 Blocking input
The tripping output relay and the signal relay for negative sequence current will be blocked if the
auxiliary voltage is connected to (terminals) D8/E8.
3.1.4 External reset input
Please refer to 5.4.

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3.2 Display
Function Display shows Pressed pushbutton Corresponding
LED
Normal operation WW
Measured operating
values
Actual measured value,
related to IN
<SELECT/RESET>
one time for each value
L1, L2, L3, I2
Setting values:
negative sequence current
warning
pickup value
I2W related to IN
<SELECT/RESET>
<+><->
I2W
time delay for negative
sequence current warning
setting value in seconds <SELECT/RESET> tW
negative sequence current
tripping
pickup value
I2S related to IN
<SELECT/RESET> I2S
tripping characteristics DEFT
INVS
<SELECT/RESET> CHAR
thermal time constant/
tripping time
Thermal time constant in
case of „INVS“ or tripping
time in case of „DEFT“ in
seconds
<SELECT/RESET> T
Function blockade EXIT <+> until max. setting value LED of blocked
parameter
Nominal frequency f = 50; f = 60 <SELECT/RESET>
<+><->
Slave address of serial in-
terface
1 - 32 <SELECT/RESET> RS
Recorded fault data IL1, IL2, IL3, I2 <SELECT/RESET>
one time for each phase
L1, L2, L3, I2, >,
>>
Save parameter? SAV? <ENTER>
Save parameter! SAV! <ENTER> for about 3 s
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 after fault tripping
Secret password input XXXX <SELECT/RESET>
<+><-><ENTER>
System reset WW <SELECT/RESET> for
about 3 s
Table 3.1: possible indication messages on the display

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 7
Figure 3.1: Front plate
3.3 LEDs
The LEDs L1, L2, L3 and I2 left to the display are bi-colored LED. Green indicates measuring, red
fault values.
The LED marked with letters RS lights up during setting of the slave address of the device for serial
data communication.
In accordance with the display 5 LEDs under the <SELECT/RESET> pushbutton indicate the se-
lected menu point.
The LEDs > and >> indicate pickup of the alarm relay (LED >) or trip relay (LED >>).

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8 DOK-TD-MRS1 Rev.A
4.Working principle
4.1 Analog circuits
The incoming currents from the main current transformers of the protected object are converted to
voltage signals in proportion to the currents via the burdened input transformers. The noise signals
caused by inductive and capacitive coupling are suppressed by an analog R-C filter circuit.
The analog voltage signals are fed to the A/D-converter of the microprocessor and transformed to
digital signals through Sample- and Hold- circuits. The analog signals are sampled at fn = 50 Hz
(60 Hz) with a sampling frequency of 800 Hz (960 Hz), namely, a sampling rate of 1.25 ms (1.04
ms) for every measuring quantity.
4.2 Digital circuits
The essential part of the MRS1 relay is a powerful microcontroller. All of the operations, from the
analog digital convertion 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).
The calculated actual negative sequence current values are compared with the relay settings. If a
negative sequence current exceeds the pickup value, an alarm is given and after the set trip 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 through a built-in "watchdog" timer. In case of a failure the
watchdog timer resets the microprocessor and gives an alarm signal via the output relay "self su-
pervision".

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 9
4.3 Principle of negative sequence protection
An unbalanced-load can be caused due to unequal distribution of current in the grid on account of
unequal loading, unsymmetrical line-to-line short-circuits (one phase and two phase), line interrup-
tion and also switching operations.
Through the unbalanced-load, negative sequence currents occur in the stator, which cause higher
harmonics with odd numbers in the stator winding and higher harmonics with even numbers in the
rotor winding. The rotor is particularly endangered in this because the higher harmonics put extra
load on the rotor winding and induce eddy currents in massive iron content of the rotor which can
even lead to melting of the metal or to the destruction of the metal structure.
An unbalanced-load is, however, permissible in certain limits and with regard to the thermal loading
limit of the generator. In order to avoid a premature outage of the generator in case of unbalanced-
load, the tripping characteristic of the negative sequence protection should be adapted to the ther-
mal characteristic of the generator.
Basically it is established that the better the cooling of the rotor, the lower are generally the per-
missible negative sequence values. This is due to the fact that with better rotor-cooling the maxi-
mum permissible symmetrical load can be chosen higher, however in relation to that, an unba-
lanced-load is permissible to a lesser extent. For turbo-generators the value of the permissible un-
balanced-load is relatively low. Usual values are approx. 10 - 15 % of the load which is permissible
with symmetrical load.
The negative sequence relay MRS1 has a large number of adjustable tripping characteristics.
Protection of almost every type of generator is thereby possible.
In case of unsymmetrical short-circuits in the grid the negative sequence protection relay normally
also picks up. In order to ensure selectivity, to the extent the overload carrying capacity of the ge-
nerator permits it, a tripping time longer than that of the mains protection (e.g. overload protection)
is to be selected.

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4.3.1 Measurement principle
A rotating three-phase system can be split according to the method of "Symmetrical Components"
into a positive-sequence system, a negative-sequence system and a zero-sequence system. The
current in the negative-sequence system is a measure for the magnitude of the unbalanced-load.
The MRS1 relay produces a negative-sequence system by rotating the current-vector IL2 by 240°
and the current-vector IL3 by 120°.
Figure 4.1: Symmetrical components
A rotating field is produced with opposite direction of rotating field. If the currents of this negative-
sequence system are added, the sum is zero in case of a symmetrically load (Fig. 4.1).
Figure 4.2: Three-phase system with unbalanced load
Fig. 4.2 shows the current vectors of an asymmetrically loaded generator. The MRS1 relay forms
the negative-sequence system by rotation and adding of the current vectors. Tripping takes place
according to the adjusted tripping-characteristic. For exact rotation of the current vectors by 120° or
240°, the accurate setting of the system frequency is necessary. (Refer to chapter 5.2.6)

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 11
Definition of the inverse current (I2)
The inverse current (negative sequence current) is the resultant current in the negative-sequence
sys-tem after splitting an unsymmetrical system in three symmetrical components. Example: In
case of a three-phase generator which is loaded with rated current in only one phase, there is an
inverse current of I2 = 1/3 x IN.
Adaptation to the generator
For matching the MRS1 relay to the respective generator-type, two important generator-parameters
are required from the generator manufacturer:
a) The continuously permissible negative sequence related to the rated current (IN) of the
generator.
K
2= I2S/IN
This is usually given in % where I2S is the continuously permissible negative sequence current.
b) The generator-constant which is dependent on design
K
1= K2
2x t
For generator with air-cooling, following values are common:
Generator capacity <100 MVA <20 MVA
Continuously permissible unba-
lanced-load K2
approx. 8...10 % x INapprox.
40 % x IN
Generator constant K130 60
Further values can be taken from DIN 57 530 part 1/IEC VDE 0530 part 1.
The maximum permissible time tperm of the negative sequence current I2is given by:


󰇛/󰇜1;  1/

The functional relationship is described graphically in chapter 7.4. In case of an occurrence of un-
balanced-load, the thermal load of the generator prior to it, is taken into account. Should after a
pickup of MRS1 relay, the I2s value drop, the time elapsed is calculated backwards exponentially.

Woodward Manual MRS1 GB
12 DOK-TD-MRS1 Rev.A
Example of setting
The following parameters may be given:
Nominal current of generator: 800 A
Current-transformer ratio: 1000/5
Continuously permissible
Unbalanced-load K2: 40 %
Thermal generator constant K1: K2
2x t = 60 s
At first the calculation is done for the generator nominal current related to the secondary side of
current transformer:
I
Nsec = 800 A x 5 / 1000 = 4 A
The continuously permissible negative sequence current related to the secondary side of the cur-
rent transformer amounts to:
I
2Ssec = 0.4 x 4 A = 1,6 A
The pickup value I2S of the negative sequence cur-rents (related to IN= 5A) can be calculated to:
I
2S = 1.6 A / 5 A = 0,32
The time-constant T for the selection of the tripping characteristic can be calculated as follows:
T = K1 / K2
2= 60 s / 0.16 = 375 s 360 s
The adjustable time-constant on the MRS1 relay amounts to 360 s.
For the warning stage I2W, a somewhat lower value than I2S (e.g. 35 %) is used. The setting value
I2W then works out as follows:
I
2W = 35 % x IN/ Current-transformer ratio / INsec
 0.35 · 800
1000
5·5
0.28
It is recommended that the time-delay tWfor the negative sequence warning has to be adjusted to
about 5 s.

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 13
5.Operations and settings
5.1 Adjustable parameters
The user can adjust 5 parameters in all:
I2W - Negative sequence current which leads to a warning
tW- Time-delay for the warning signal
I2S - Continuously permissible negative sequence current
CHAR - Tripping characteristic (Inverse-time or definite time)
T - Thermal time-constant of the genera-tor incase of inverse-current dependent
characteristic or tripping time in case of independent characteristic
5.2 Setting procedure
For parameter setting a password has to be entered first. (Please refer to 4.4 of description "MR-
Digital Multifunctional Relays")
5.2.1 Pickup value for negative sequence warning current (I2W)
At the time of the adjustment of the pickup value of the negative sequence warning current (I2W), an
indication value related to the nominal current (IN) appears on the display.
I.e. Pickup value (I2W) = indicated value x nominal current (IN)
The desired pickup value can be adjusted with the pushbuttons <+> and <-> in the range of
0.02 to 0.5 x IN. LED I2W lights up during the adjustment.
5.2.2 Time delay for negative sequence warning (tW)
At the time of the adjustment of the time delay for the negative sequence warning (tW), an indication
value in seconds appears on the display. The de-sired time delay can be set with pushbuttons <+>
and <-> in the range of 0.1 to 20 s. LED tWlights up during the
adjustment.
5.2.3 Pickup value for negative sequence current (I2S)
At the time of adjustment of the pickup value for the negative sequence current (I2S), an indication
value related to the nominal current (IN) appears on the display. The desired pickup value can be
selected with pushbuttons <+> and <-> in the range of 0.02 to 0.5 x IN. LED I2S lights up during the
adjustment.
5.2.4 Tripping characteristic (CHAR)
At the time of the adjustment of the tripping characteristic (CHAR), either the letters "DEFT" for in-
dependent or "INVS" for an inverse-current dependent tripping characteristic appear on the display.
The desired tripping characteristic can be selected with the pushbuttons <+> and <->. LED CHAR
lights up during the adjustment.
5.2.5 Trip delay / thermal time-constant (T)
If an independent tripping characteristic has been chosen as described in chapter 5.2.4 the value
shown on the display corresponds to the trip delay in seconds. If an inverse current dependent trip-
ping characteristic has been chosen the displayed value corresponds to the thermal time-constant
in seconds. The desired value can be adjusted with the pushbuttons <+> and <->. LED T lights up
during the adjustment.

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5.2.6 Rated frequency
By pressing <SELECT> the display shows "f=50" or "f=60". The desired nominal frequency can be
adjusted by <+> or <-> and then stored with <ENTER>.
5.2.7 Adjustment of the slave address
Pressing pushbuttons <+> and <-> the slave ad-dress can be set in the range of 1 -32.
5.3 Indication of measuring values and fault data
5.3.1 Indication of measuring values
Phase current in phase 1 (LED L1)
Phase current in phase 2 (LED L2)
Phase current in phase 3 (LED L3)
Negative sequence current (LED I2)
5.3.2 Indication of fault data
All faults detected by the relay are indicated on the front plate optically. LEDs I2, > and >> are
avail-able for this purpose. At the time of an unbalanced load warning, LED ">" flashes for the dura-
tion of the time delay and then changes over to steady light.
In case of a negative sequence activation, the LEDs ">" and ">>" flash for the duration of the time
delay and then both of them change to steady light. After tripping, the LED "I2" lights up with an
additional steady red light.
5.4 Reset
Unit MRS1 has 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 pushbutton <SELECT/RESET> for some time (about 3 seconds)
Electrical Reset
Through applying auxiliary voltage to C8/D8
Software Reset
The software reset has the same effect as the <SELECT/RESET> pushbutton (see also
communication 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.

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 15
6.Relay testing and commissioning
The following test instructions should help to verify the protection relay performance before or dur-
ing commissioning 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 current and rated voltage of the relay correspond to the plant data on site.
the current transformer circuits and voltage trans-former circuits are connected to the relay
correctly.
all signal circuits and output relay circuits are connected correctly.
6.1 Power-On
NOTE!
Prior to switch on the auxiliary power supply, be sure that the auxiliary supply voltage corresponds
with the rated data on the type plate.
Switch on the auxiliary power supply to the relay and check that the message "WW" appears on
the display and the self supervision alarm relay (watchdog) is energized (Contact terminals D7 and
E7 closed).
6.2 Testing the output relays
Note !
Prior to commencing this test, always block the output circuits or interrupt in another way the output
circuits which can cause the tripping of the circuit breaker if the breaker operation during this test is
not desired.
By pressing the pushbutton <TRIP> once the display shows you the first part of the software ver-
sion of the relay (e.g. „D08-“). By pressing the pushbutton <TRIP> twice the display shows the
second part of the software version of the relay (e.g. „4.01“). The software version should be
quoted in all correspondence. After you have got a message "PSW?" on the display by pressing
the pushbutton <TRIP> once more please enter the correct password to proceed with the test. Af-
ter that the message "TRI?" will follow. Confirm this testing by means of pressing pushbutton
<TRIP> again. All output relays should then be activated and the self supervision alarm relay
(watchdog) be deactivated one after another with a time interval of 1 second. Thereafter, reset all
output relays back to their normal positions by pressing the pushbutton <SELECT/RESET>.
6.3 Checking the set values
By repeatedly pressing the pushbutton <SELECT> all relay set values may be checked and set
value modification can be done with the pushbutton <+><-> and <ENTER>. For detailed informa-
tion about that, please refer to chapter 5.
For a correct relay operation, be sure that the frequency set value (f=50/60) has been selected
correctly according to your system frequency (50 or 60 Hz).

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6.4 Secondary injection test
6.4.1 Test equipment
Ammeter with class 1 or better
Auxiliary power supply with the voltage corresponding to the rated data on the type plate
Single-phase current supply unit or three-phase current supply unit with adjustable phase
shifting (adjustable from 0 to 1x IN)
Timer to measure the operating time (Accuracy class 10 ms)
Switching device
Test leads and tools
6.4.2 Example of test circuit for MRS1 relay
For testing MRS1 relays, you need usually a three phase current test circuit with adjustable phase
shifting to simulate various asymmetrical system conditions. Yet you can also use a single-phase
test circuit. The figure 6.1 shows a simple example of a single phase test circuit with adjustable cur-
rent energizing the MRS1 relay under test.
Figure 6.1: Single-phase test circuit
6.4.3 Checking the input circuits and measured values
Inject a current of rated value (1A or 5 A) in phase 1 (terminals B3-B4, as shown in figure 1), and
check the measured currents on the display by pressing the pushbutton <SELECT>. The current in
phase 1 (LED L1) should be indicated on display as about 1.0 (x IN), while the currents in phase 2
and 3 (LED L2 and L3) should be zero. Compare the reading of current in display with the reading
in ammeter. The deviation must not exceed 5 %. The negative sequence current (LED I2) should
be indicated on display as about 0.33 x IN. The current can be also injected into the other current
input circuits (Phase 2: terminals B5 - B6, Phase 3: terminals B7 - B8) in the same manner.

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The negative sequence current to be measured should have the same value as in test of phase 1.
By using an RMS-metering instrument, a greater deviation may be observed if the test current
contains harmonics. Because the MRS1 relay measures only the fundamental component of the
input signals. The harmonics will be rejected using a DFFT-digital filter. Whereas the RMS-
metering instrument measures the RMS-value of the input signals.
In the following table, the negative sequence cur-rents in different cases are summarized. If you
have a three-phase test circuit with phase shifting in each output, this table will help you to check
the relay under various asymmetrical system conditions:
Input currents Negative Se- quence current
IR(x IN) Angle (°) IS(x IN) Angle (°) IT(x IN) Angle (°) I2(x IN)
1.00 - 0 - 0 - 0.33
0 - 1.00 - 0 - 0.33
0 - 0 - 1.00 - 0.33
1.00 0 1.00 240 1.00 120 1.00
1.00 0 1.00 120 1.00 240 0
1.00 0 1.00 180 0.00 - 0.578
0 - 1.00 0 1.00 120 0.33
6.4.4 Checking the operating and resetting values of the relay
Inject a current which is less than 3-times the relay set values in phase 1 of the relay and gradually
in-crease the current until the relay starts, i.e. at the moment when the LED I2 lights up. Read the
operating current indicated by the ammeter. The operating negative sequence current I2 can be
calculated by dividing the indicated operating current with three. (Note the difference between the
operating current and the operating negative sequence current.) The deviation of the operating
negative sequence current I2must not exceed 5 % of the set value.
Furthermore, gradually decrease the current until the relay resets, i.e. the LED I2 stop flashing
quickly and begin to flashing slowly. Check that the resetting current is greater than 0.95 times the
operating current.
Repeat the test on phase 2, phase 3 current input circuits in the same manner.
6.4.5 Checking the relay operating time
To check the relay operating time, a timer must be connected to the trip output relay contact. The
timer should be started simultaneously with the current injection in the current input circuit and
stopped by the trip relay contact. Set the current to a value corresponding to twice the operate val-
ue and inject the current instantaneously. The operating time measured by timer should have a
deviation about < 3 % of the set value or < 20 ms.
Repeat the test on the other phases or with the in-verse time characteristics in the similar manner.
In case of inverse time characteristics the injected current should be selected according to the cha-
racteristic curve, e.g. two times I2s. The tripping time may be red from the characteristic curve dia-
gram or calculated with the equations given under "technical data". The operating time for inverse
time characteristics measured by timer should have a deviation about < 7.5 %. Please observe that
test current during the secondary injection test must be very stable, not deviating more than 1 %.
Otherwise the test results may be wrong.

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6.4.6 Checking the extern blocking and reset functions
By MRS1 relays, the trip element will be inhibited by extern blocking input. To test the blocking
function apply auxiliary supply voltage to extern blocking input of the relay (terminals E8/D8). Inject
a test current which could cause a tripping. Observe that there is no trip and alarm.
Remove the auxiliary supply voltage from the blocking input. Inject test current to make the relay
tripped (Message „TRIP“ on the display). Interrupt the test current and apply auxiliary supply vol-
tage to extern reset input of the relay (terminals C8/D8). The display and LED indications should be
reset immediately.
6.5 Primary injection test
Generally, a primary injection test could be carried out in the similar manner as the secondary in-
jection test above described, with the difference that the protected power system should be, in this
case, connected to the installed relays under test „on line“, and the test currents and voltages
should be injected to the relay through the current and voltage transformers with the primary side
energized. Since the cost and potential hazards are very high for such a test, primary injection tests
are usually limited to very important protective relays to the power system.
Because of its powerful combined indicating and measuring functions the MRS1 may be tested in
the manner of a primary injection without extra expenditures and time consumption.
In actual service, for example, the measured cur-rent values on the MRS1 relay display may be
compared phase by phase with the current indications of the ammeter on the switch-board panel to
verify that your relay works and measures correctly. If you have symmetrical three phase load cur-
rents in your power system, you can check if the negative sequence current measured on relay
display is zero as to verify that the relay is connected to the power system correctly.
6.6 Maintenance
Maintenance testing is generally done on site at regular intervals. These intervals vary among us-
ers depending 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 relay, etc.
For electromechanical or static relays, maintenance testing will be performed at least once a year
according to the experiences. For digital re-lays like MRS1, this interval can be substantially longer.
This is because that:
the MRS1 relays are equipped with very wide self-supervision functions, so that many
faults in the relay can be detected and signalized during the service. Important: The self-
supervision out-put relay must be connected to a central alarm panel!
the combined measuring functions in MRS1 relay enable supervision the relay functions
during service.
the combined TRIP test function of the MRS1 relay allows to test the relay output circuits
by power system interrupt.
A testing interval of two years for maintenance will, therefore, be recommended.
During a maintenance testing, the relay functions including the operating values and relay tripping
characteristics as well as the operating time should be tested.

Manual MRS1 GB Woodward
DOK-TD-MRS1 Rev.A 19
7.Technical data
MRS1 - Digital Multifunctional Relay for negative sequence protection
7.1 Measuring input circuits
Rated data: Nominal current IN1A or 5A
Nominalfrequencyf
N50 Hz; 60 Hz adjustable
Power consumption in
current circuit: at IN= 1 A 0.2 VA
atI
N= 5 A 0.1 VA
Power consumption in
voltage circuit: < 1 VA
Thermal withstand capability
in current circuit: dynamic current withstand
(half-wave) 250 x IN
for 1 s 100 x IN
for10s 30xI
N
continuously 4 x IN
7.2 Common data
Dropout to pickup ratio: 95 % - 97 %
Returning time: 80 ms
Time lag error class index E: ± 20 ms
Minimum operating time: 100 ms
Transient overreach at
instantaneous operation: ≤5 %
Influences to the negative sequence
current measuring:
Harmonics: at 20 % of the third harmonic: ≤1,2 %
at 20 % of the fifth harmonic: ≤0,5 %
Frequency: in the range of 0,9 < f/fN< 1,1: < 2,5 %/Hz
7.3 Setting ranges and steps
Setting range Step Pickup tolerances
I2W
tW
0.02...0.5 x IN
0.1...20 s
0.005; 0.01; 0.02 x IN
0.1; 0.2; 0.5; 1.0 s

5 % of set value
3 % or 10 ms
I2S 0.02...0.5 x IN0.005; 0.01; 0.02 x IN

5 % of set value
T(DEFT)
T(INVS)
1...200 s
300...3600 s
0.2; 0.5; 1; 2; 5; 10; 20 s
30; 60; 120; 300 s

3 %
7.5 % by I2/I2S = 10
Figure 7.1: Setting ranges and steps
Inverse time current protection
 
󰇛/󰇜
Where: t = tripping time [s]
T = thermal time-constant
I
2= measured negative sequence current related to IN
I
2S = continuously permissible negative sequence current
relatedtoI
N

Woodward Manual MRS1 GB
20 DOK-TD-MRS1 Rev.A
7.4 Tripping characteristic
Figure 7.2: Tripping characteristic
7.5 Output contact ratings
Number of relays: 4
Contacts: 2 change-over contacts for trip relay
1 change-over contact for alarm relays