Woodward MRI3 User manual

MRI3 – Digital multifunctional relay
for overcurrent protection
Manual MRI3 (Revision A)

Woodward Manual MRI3 GB
2 DOK-TD-MRI3 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-
sumed by Woodward Governor Company unless otherwise expressly undertaken.
© Woodward 1994-2008

Manual MRI3 GB Woodward
DOK-TD-MRI3 Rev.A 3
Contents
1.Introduction and application.......................................................................5
2.Features and characteristics ......................................................................6
3.Design...........................................................................................................7
3.1Connections ........................................................................................................................7
3.1.1Analog input circuits ........................................................................................................9
3.1.2Output relays ...................................................................................................................9
3.1.3Blocking input ................................................................................................................10
3.1.4External reset input .......................................................................................................10
3.2Relay output contacts........................................................................................................10
3.2.1Fault recorder ................................................................................................................11
3.2.2Parameter settings (see chapter 5)...............................................................................12
3.3LEDs..................................................................................................................................17
4.Working principle.......................................................................................18
4.1Analog circuits ...................................................................................................................18
4.2Digital circuits ....................................................................................................................18
4.3Directional feature .............................................................................................................19
4.3.1Reversal in direction during the activation phase .........................................................19
4.4Earth fault protection .........................................................................................................23
4.4.1Generator stator earth fault protection ..........................................................................23
4.4.2System earth fault protection ........................................................................................23
4.5Earth-fault directional feature (ER/XR-relay type).............................................................24
4.6Determining earth short-circuit fault direction (SR/YR-relay type) .................................26
4.6.1Directly – earthed system..............................................................................................26
4.6.2Resistance – earthed system........................................................................................27
4.6.3Connection possibilities of the voltage transformers for SR relay types.......................28
4.7Demand imposed on the main current transformers.........................................................28
5.Operation and settings..............................................................................29
5.1Display...............................................................................................................................29
5.2Setting procedure..............................................................................................................30
5.3System parameter.............................................................................................................31
5.3.1Display of measuring values as primary quantities (Iprim phase)...................................31
5.3.2Display of earth current as primary quantity (Iprim earth) ...............................................31
5.3.3Display of residual voltage UEas primary quantity (Uprim/Usec) .....................................31
5.3.4Voltage transformer connection for residual voltage measuring (3pha/e-n/1:1)...........31
5.3.5Nominal frequency ........................................................................................................31
5.3.6Display of the activation storage (FLSH/NOFL)............................................................32
5.3.7Parameter switch/external triggering of the fault recorder ............................................32
5.4Parameter protection.........................................................................................................33
5.4.1Pickup current for phase overcurrent element (I>) .......................................................33
5.4.2Time current characteristics for phase overcurrent element (CHAR I>).......................33
5.4.3Trip delay or time factor for phase overcurrent element (tI>)........................................33
5.4.4Reset setting for all tripping characteristics in the phase current path .........................34
5.4.5Current setting for high set element (I>>) .....................................................................34
5.4.6Trip delay for high set element (tI>>) ............................................................................34
5.4.7Relay characteristic angle RCA ....................................................................................34
5.4.8Pickup value for residual voltage UE (ER/XR-relay type).............................................34
5.4.9Pickup current for earth fault element (IE>) ..................................................................34
5.4.10WARN/TRIP changeover (all earth fault-relay type) .................................................35
5.4.11Time current characteristics for earth fault element (CHAR IE) (not for ER/XR-relay
type) 35
5.4.12Trip delay or time multiplier for earth fault element (tIE>>) .........................................35
5.4.13Reset mode for inverse time tripping in earth current path.......................................35
5.4.14Current setting for high set element of earth fault supervision (IE>>).........................35
5.4.15Trip delay for high set element of earth fault supervision (tIE>>)................................35
5.4.16COS/SIN Measurement (ER/XR-relay type) .............................................................35
5.4.17SOLI/RESI changeover (SR/YR-relay type) .............................................................36
5.4.18Block/Trip – time........................................................................................................36

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5.4.19Circuit breaker failure protection tCBFP ................................................................... 36
5.4.20Adjustment of the slave address .............................................................................. 36
5.4.21Setting of Baud-rate (applies for Modbus Protocol only).......................................... 36
5.4.22Setting of parity (applies for Modbus Protocol only)................................................. 36
5.5Fault recorder ................................................................................................................... 37
5.5.1Adjustment of the fault recorder ................................................................................... 37
5.5.2Number of the fault recordings ..................................................................................... 37
5.5.35.5.3 Adjustment of trigger occurrences....................................................................... 37
5.5.4Pre-trigger time (Tpre) .................................................................................................. 37
5.6Adjustment of the clock..................................................................................................... 38
5.7Additional functions........................................................................................................... 38
5.7.1Blocking the protection functions and assignment of the output relays ....................... 38
5.8Setting value calculation ................................................................................................... 40
5.8.1Definite time overcurrent element................................................................................. 40
5.8.2Inverse time overcurrent element ................................................................................. 41
5.9Indication of measuring and fault values .......................................................................... 41
5.9.1Indication of measuring values ..................................................................................... 41
5.9.2Units of the measuring values displayed ..................................................................... 42
5.9.3Indication of fault data................................................................................................... 44
5.9.4Fault memory................................................................................................................ 44
5.10Reset................................................................................................................................. 45
5.10.1Erasure of fault storage ............................................................................................ 45
6.Relay testing and commissioning............................................................46
6.1Power-On.......................................................................................................................... 46
6.2Testing the output relays and LEDs ................................................................................. 46
6.3Checking the set values.................................................................................................... 46
6.4Secondary injection test.................................................................................................... 47
6.4.1Test equipment ............................................................................................................. 47
6.4.2Example of test circuit for MRI3 relays without directional feature............................... 47
6.4.3Checking the input circuits and measured values ........................................................ 48
6.4.4Checking the operating and resetting values of the relay ............................................ 48
6.4.5Checking the relay operating time ................................................................................ 48
6.4.6Checking the high set element of the relay .................................................................. 48
6.4.7Example of a test circuit for MRI3 relay with directional feature................................... 49
6.4.8Test circuit earth fault directional feature...................................................................... 51
6.4.9Checking the external blocking and reset functions ..................................................... 52
6.4.10Testing the external blocking with Block/Trip function.............................................. 52
6.4.11Test of the CB failure protection ............................................................................... 52
6.5Primary injection test ........................................................................................................ 53
6.6Maintenance ..................................................................................................................... 53
7.Technical data............................................................................................54
7.1Measuring input circuits .................................................................................................... 54
7.2Common data ................................................................................................................... 54
7.3Setting ranges and steps .................................................................................................. 55
7.3.1Time overcurrent protection (I-Type) ............................................................................ 55
7.3.2Earth fault protection (SR/YR-Type)............................................................................. 55
7.3.3Earth fault protection (E/X-Type) .................................................................................. 55
7.3.4Earth fault protection (ER/XR-Type)............................................................................. 56
7.3.5Block/Trip – time ........................................................................................................... 56
7.3.6Switch failure protection................................................................................................ 56
7.3.7Interface parameter ...................................................................................................... 56
7.3.8Parameter for the fault recorder ................................................................................... 56
7.3.9Inverse time overcurrent protection relay ..................................................................... 57
7.3.10Direction unit for phase overcurrent relay................................................................. 58
7.3.11Determination of earth fault direction (MRl3-ER/XR)................................................ 58
7.3.12Determination of earth fault direction (MRl3-SR/YR)................................................ 58
7.4Inverse time characteristics .............................................................................................. 59
7.5Output contacts................................................................................................................. 62
8.Order form..................................................................................................63

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DOK-TD-MRI3 Rev.A 5
1.Introduction and application
The MRl3 digital multifunctional relay is a universal time overcurrent and earth fault protection de-
vice intended for use in medium-voltage systems, either with an isolated/compensated neutral point
or for networks with a solidly earthed/resistance-earthed neutral point.
The protective functions of MRI3 which are implemented in only one device are summarized as fol-
lows:
Independent (Definite) time overcurrent relay,
inverse time overcurrent relay with selectable characteristics,
integrated determination of fault direction for application to doubly infeeded lines or
meshed systems,
two-element (low and high set) earth fault protection with definite or inverse time
characteristics,
integrated determination of earth fault direction for application to power system networks
with isolated or arc suppressing coil (Peterson coil) neutral earthing. (ER/XR-relay type),
integrated determination of earth short-circuit fault direction in systems with solidly-earthed
neutral point or in resistance-earthed systems (SR-relay type).
Furthermore, the relay MRI3 can be employed as a back-up protection for distance and differential
protective relays.
A similar, but simplified version of overcurrent relay IRI1 with reduced functions without display and
serial interface is also available.
Important:
For additional common data of all MR-relays please refer to manual "MR - Digital Multifunctional
relays". On page 66 of this manual you can find the valid software versions.

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2.Features and characteristics
Digital filtering of the measured values by using discrete Fourier analysis to suppress the
high frequence harmonics and DC components induced by faults or system operations,
two parameter sets,
selectable protective functions between:
- definite time overcurrent relay and
- inverse time overcurrent relay,
selectable inverse time characteristics according to IEC 255-4:
- Normal Inverse (Type A)
- Very Inverse (Type B)
- Extremely Inverse (Type C)
- Special characteristics,
reset setting for inverse time characteristics selectable,
high set overcurrent unit with instantaneous or de-finite time function,
two-element (low and high set) overcurrent relay both for phase and earth faults,
directional feature for application to the doubly in-feeded lines or meshed systems,
earth fault directional feature selectable for either isolated or compensated networks,
sensitive earth fault current measuring with or without directional feature
(X and XR-relay type),
determination of earth short-circuit fault direction for systems with solidly-earthed or
resistance-earthed neutral point,
numerical display of setting values, actual measured values and their active, reactive
components, memorized fault data, etc.,
display of measuring values as primary quantities,
withdrawable modules with automatic short circuiters of C.T. inputs when modules are
withdrawn,
blocking e.g. of high set element (e.g. for selective fault detection through minor
overcurrent protection units after unsuccessful AR),
relay characteristic angle for phase current directional feature selectable,
circuit breaker failure protection,
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,
free assignment of output relays
serial data exchange via RS485 interface possible; alternatively with
SEG RS485 Pro-Open Data Protocol or Modbus Protocol,
suppression of indication after an activation (LED flash),
display of date and time

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3.Design
3.1 Connections
Phase and earth current measuring:
Figure 3.1: Measuring of the phase currents for over-current- and short-circuit protection (I>,I>>)
Figure 3.2: Earth-fault measuring by means of ring-core C.T. (IE)
When phase-- and earth-fault current measuring are combined, the connection has to be realized
as per Figure 3.1 and Figure 3.2 or Figure 3.3.

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Figure 3.3: Phase current measuring and earth-current detection by means of Holmgreen-circuit.
This connection can be used with three existing phase current transformers when combined phase
and earth-current measuring is required.
Disadvantage of holmgreen-circuit:
At saturation of one or more C.Ts the relay detects seeming an earth current.
* This arrow shows the current flow in forward direction, for this LED →← lights up green
Voltage measuring for the directional detection:
Figure 3.4: Measuring of the phase voltages for the directional detection at overcurrent, short-circuit or earth-fault
protection (I>, I>>, IE> and IE>>).
For details on the connection of ER/XR-unit type c.t.s, see para 4.5.

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Figure 3.5: Voltage transformer in V-connection for the directional detection at overcurrent and short-circuit protection.
The V-connection cannot be applied at earth fault directional feature.
3.1.1 Analog input circuits
The protection unit receives the analog input signals of the phase currents IL1 (B3-B4), IL2 (B5-
B6), IL3 B7-B8) and the current IE (B1-B2), phase voltages U1 (A3), U2 (A5), U3 (A7) with A2 as
star point, each via separate input transformers.
The constantly detected current measuring values are galvanically decoupled, filtered and finally
fed to the analog/digital converter.
For the unit type with earth fault directional features (ER/XR-relay type) the residual voltage UE in
the secondary circuit of the voltage transformers is internally formed.
In case no directional feature for the phase current path is necessary the residual voltage from the
open delta winding can directly be connected to A3 and A2.
See Chapter 4.5 for voltage transformer connections on isolated/compensated systems.
3.1.2 Output relays
The MRI3 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: Self-supervision C7, D7, E7
All trip and alarm relays are working current relays, the relay for self supervision is an idle current
relay.

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3.1.3 Blocking input
The blocking functions adjusted before will be blocked if an auxiliary voltage is connected to
(terminals) D8/E8. (See chapter 5.7.1)
3.1.4 External reset input
Please refer to chapter 5.10.
3.2 Relay output contacts
Figure 3.6:

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3.2.1 Fault recorder
The MRI3 is equipped with a disturbance value recorder which records the measured analogue
values as momentary values. The momentary values
iL1, iL2, iL3, iE,
are scanned within a grid 1.25 ms (with 50 Hz) or 1.041 ms (with 60 Hz) and filed in a circulating
storage. The max. storage capacity amounts to 16 s (with 50 Hz) or 13.33 s (with 60 Hz).
Storage division
Independent of the recording time, the entire storage capacity can be divided into several cases of
disturbance with a shorter recording time each. In addition, the deletion behaviour of the fault re-
corder can be influenced.
No writing over
If 2, 4 or 8 recordings are chosen, the complete memory is divided into the relevant number of par-
tial segments. If this max. number of fault event has been exceeded, the fault recorder block any
further recordings in order to prevent that the stored data are written over. After the data have been
read and deleted, the recorder to ready again for further action.
Writing over
If 1, 3 or 7 recordings are chosen, the relevant number of partial segments is reserved in the com-
plete memory. If the memory is full, a new recording will always write over the oldest one.
The memory part of the fault recorder is designed as circulating storage. In this example 7 fault
records can be stored (written over).
Memory space 6 to 4 is occupied.
Memory space 5 is currently being written in
Figure 3.7: Division of the memory into 8 segments, for example
Since memory spaces 6, 7 and 8 are occupied, this example shows that the memory has been as-
signed more than eight recordings. This means that No. 6 is the oldest fault recording and No. 4
the most recent one.

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Figure 3.8: Recording scheme of the fault recorder with pre-trigger time
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 with HTL/PL-Soft4.
The data is graphically edited and displayed. Binary tracks are recorded as well, e.g. activation and
trip.
3.2.2 Parameter settings (see chapter 5)
System parameter
Relay type MRI3- I IE
IX IRE IRX IR IER IXR IRER IRXR ER XR EX ISR IRSR SR
Display of measuring val-
ues as primary quantities
(I
p
rim phase)
X X X X X X X X
Display of earth current as
primary quantities (Iprim
earth)
X X X X X X X X X
Display of residual voltage
UE as primary quantity
(U
p
rim/Usec)
X X X
3pha/e-n/1:1 X X X
50/60 Hz X X X X X X X X X X X
LED-Flash X X X X X X X X X X X
RS 485 slave address X X X X X X X X X X X
Baud-Rate
1)
X X X X X X X X X X X
Parity-Check
1)
X X X X X X X X X X X
Adjustment of the clock:
Y = year; M = month;
D = day; h = hour;
m = minute; s = sec.
X X X X X X X X X X X
Table 3.1: System parameters of the different relay types
1) Only devices with Modbus-Protocol
trigger occurence
recording duration
Tpre
[s]

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Protection parameter
Relay type MRI3- I IE
IX IRE IRX IR IER IXR IRER IRXR ER XR EX ISR IRSR SR
2 parameter sets X X X X X X X X X X X
I> X X X X X X X X
CHAR I> X X X X X X X X
tI> X X X X X X X X
0s /60s
2)
X X X X X X X X
I>> X X X X X X X X
tI>> X X X X X X X X
RCA X X X X
UEX X X
IE> X X X X X X X X X
warn/trip X X X X X X
CHAR IEX X X X X X
tIE X X X X X X X X X
0s / 60s
3)
X X X X X X
IE>> X X X X X X X X X
tIE>> X X X X X X X X X
sin/cos X X X
soli/resi X X X
tCBFP X X X X X X X X X X X
Block/Trip X X X X X X X X X X X
Table 3.2: Protection parameters of the different relay types.
2) Reset setting for inverse time characteristics in phase current path
3) Reset setting for inverse time characteristics in earth current path
Parameter for the fault recorder
Relay type MRI3- I IE
IX IRE IRX IR IER IXR IRER IRXR ER XR E X ISR IRSR SR
Number of fault events X X X X X X X X X X X
Trigger events X X X X X X X X X X X
Pre-trigger time (Tpre) X X X X X X X X X X X
Table 3.3: Parameters for the fault recorder of the different relay types
Additional parameters
Relay type MRI3- I IE
IX IRE IRX IR IER IXR IRER IRXR ERX R E X ISR IRSR SR
Blocking mode
1)
X X X X X X X X X X X
Relay parameterizing X X X X X X X X X X X
Fault recorder X X X X X X X X X X X
Table 3.4: Additional parameters of the different relay types
1) For 2 parameter sets (separately for each parameter set)

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Front plates
Figure 3.9: Front plate MRI3-I
Figure 3.10: Front plate MRI3-E/X

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Figure 3.11: Front plate MRI3-IR
Figure 3.12: Front plate MRI3-ER/XR

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Figure 3.13: Front plate MRI3-SR
Figure 3.14: Front plate MRI3-IRER/IRXR and MRI3-IER/IXR

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Figure 3.15: Front plate MRI3-IRSR; MRI3-IRE/IRX, MRI3-IRYR and MRI3-ISR
3.3 LEDs
The LEDs left from the display are partially bi-colored, the green indicating measuring, and the red
fault indication.
MRI3 with directional feature have a LED (green- and red arrow) for the directional display. At
pickup/trip and parameter setting the green LED lights up to indicate the forward direction, the red
LED indicates the backward direction.
The LED marked with letters RS lights up during setting of the slave address of the device for serial
data communication.
The LEDs arranged at the characteristic points on the setting curves support the comfortable set-
ting menu selection. In accordance with the display 5 LEDs for phase fault overcurrent relay and 5
LEDs for earth-fault relay indicate the corresponding menu point selected.
The LED labeled with the letters LR is alight while the fault recorder is being adjusted.

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4.Working principle
4.1 Analog circuits
The incoming currents from the main current transformers on the protected object are converted to
voltage signals in proportion to the currents via the input transformers and burden. The noise sig-
nals 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 at 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. (16 scans per period).
Figure 4.1: Block diagram
4.2 Digital circuits
The essential part of the MRI3 relay is a powerful microcontroller. All of the operations, from the
analog digital conversion to the relay trip decision, are carried out by the microcontroller digitally.
The relay program is located in an EPROM (Electrically-Programmable-Read-Only-Memory). With
this program the CPU of the microcontroller calculates the three phase currents and ground current
in order to detect a possible fault situation in the protected object.
For the calculation of the current value an efficient digital filter based on the Fourier Transformation
(DFFT - Discrete Fast Fourier Transformation) is applied to sup-press high frequency harmonics
and DC components caused by fault-induced transients or other system disturbances.
The calculated actual current values are compared with the relay settings. If a phase current ex-
ceeds the pickup value, an alarm is given and after the set trip delay has elapsed, the correspond-
ing trip relay is activated.
The relay setting values for all parameters are stored in a parameter memory (EEPROM - Electri-
cally Erasable Programmable Read-only Memory), so that the actual relay settings cannot be lost,
even if the power supply is interrupted.
The microprocessor is supervised by a built-in "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".

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4.3 Directional feature
A built-in directional element in MRI3 is available for application to doubly infeeded lines or to ring
networks.
The measuring principle for determining the direction is based on phase angle measurement and
therefore also on coincidence time measurement between current and voltage. Since the neces-
sary phase voltage for determining the direction is frequently not available in the event of a fault,
whichever line-to-line voltage follows the faulty phase by 90° is used as the reference voltage for
the phase current. The characteristic angle at which the greatest measuring sensitivity is achieved
can be set to precede the reference voltage in the range from 15° to 83°.
Figure 4.2: Relay characteristic angle
The TRIP region of the directional element is determined by rotating the phasor on the maximum
sensitivity angle for ±90°, so that a reliable direction decision can be achieved in all faulty cases.
4.3.1 Reversal in direction during the activation phase
Reversal of the current direction during the activation phase can lead to hyper functions. This main-
ly applies to installations where parallel connected lines are monitored by current relays with direc-
tional feature. For this reason the directional determination for the phase current is shown in a time
window; this applies to all SR versions. In case of activation due to a fault, a timer is started and
measures the time in the determined direction for max. 1 s. This timer runs backwards at half
speed if, during the activation phase, a fault causes reversal of the direction. Only when the timer is
at zero again, the MRI3 recognizes the reversal in direction. The switch-over time is max. 2 s. The
activation delays tl> and tl>> are not affected by the delayed recognition of direction.
Figure 4.3: Recording scheme of the fault recorder with lead time
1.0 1.5
0.5 [s]
0.5
1.0
1.5
Trip delay at direction reversal
max. time
Recognition of direction reversal
Recognition of
backward direction
<Red LED> is alight
Recognition of
forward direction
<Green LED> is alight
Timer runs at
half speed
actual
direction reversal
t=1/2

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Figure 4.4
Figure 4.5
Example:
Figure 4.4 and Figure 4.5 illustrate a possible fault situation with a reversal in direction in the fault-
free line. The current transformers used have a primary current of 250 A. The switch point for the I>
stage is 0.25 kA and for the I>> stage 1 kA. All devices have the same setting and will, if set to
“Forward”, recognize the direction in relation to the forward direction of the line. The critical point
here is the MRI3 No. 1. Using delay action in directional recognition, it is possible to prevent shut-
down of the fault-free line.
The following relay setting applies:
I> 1.00 x In
CHAR I> DEFT (inverse)
trip delay
tI>(V) 10s
Trip delay in forward direction
tI>(R) EXIT (no trip) Delay in backward direction
I> 4.00 x In
tI>>(V) 0.1 s
tI>>(R) EXIT
MRI3
MRI3
MRI3
MRI3
G
I
K
= 0,3 kA
I
K
= 3,61 kA
I
K
= 0,9 kA
I
K
= 3,31 kA
I
K
= 1,2 kA
l = 3 km
l = 0,5 km
l = 3 km
N
o. 2
N
o. 4
N
o. 3
N
o. 1
MRI3
MRI3
MRI3
MRI3
G
I
K
= 1,2 kA
I
K
= 2,0 kA
I
K
= 1,2 kA
I
K
= 0,8 kA
l = 0,5 km
l = 3 km
l = 3 km
N
o. 1
N
o. 3
N
o. 2
N
o. 4