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.
1.5 1.0 0.5 0.5 1.0 1.5 [ s]
Trip delay at direction reversal
max. time
Recognition of direction reversal
Recognition of
backward direction
is alight
Recognition of
forward direction
is alight
Timer runs at
half speed
actual
direction reversal
t= 1/ 2
Figure 4.3: Recording scheme of the fault recorder with lead
time
MRI3
MRI3 MRI3
MRI3
G
IK = 0, 3 kA
IK = 3, 61 kA
IK = 0, 9 kA
IK = 3, 31 kA
IK = 1, 2 kA
l = 3 km
l = 0, 5 km
l = 3 km
No. 2 No. 4
No. 1 No. 3
Figure 4.4
Example:
Figures 4.4 and 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
IK = 1, 2 kA
IK = 2, 0 kA
IK = 1, 2 kA
IK = 0, 8 kA
l = 0, 5 km
l = 3 km
l = 3 km
No. 1 No. 3
No. 2 No. 4
Figure 4.5
TD_ MRI3_ 11.07_ GB 15
If line impedance and internal resistance of the generator
is only ohmic:
If line impedance and internal resistance of the generator
is only inductive:
The maximum sensitivity angle corresponds to the R/ L
component.
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.
Figure 4.6: TRIP/ NO-TRIP region for directional element in MRI3.
In this case the foreward direction is defined as TRIP
region and the backward direction as NO-TRIP region.
By means of accurate hardware design and by using
an efficient directional algorithm a high sensitivity for
the voltage sensing circuit and a high accuracy for
phase angle measurement are achieved so that a correct
directional decision can be made even by close
three-phase faults.
As an addition, to avoid maloperations due to disturbances,
at least 2 periods ( 40 ms at 50 Hz) are
evaluated.
For the MRI3-overcurrent relays with directional feature
different time delays or time multipliers can be set for
forward and backward faults ( ref. to chapter 5.4.3) .
If the trip delay for backward faults is set longer than
the one for forward faults, the protective relay works
as a " backup" -relay for the other lines on the same
busbar. This means that the relay can clear a fault in
the backward direction with a longer time delay in
case of refusal of the relay or the circuit breaker on the
faulted line.
If the trip delay for backward faults is set out of range
( on the display " EXIT" ) , the relay will not trip in case of
backward faults.
The assignment of the output relays can be used to select
in which direction the failure is to be indicated ( refer
also to Chapter 5.7.1) . It is possible to indicate the
activation and/ or the tripping for each tripping direction
via the output relays.
16 TD_ MRI3_ 11.07_ GB
4.4 Earth fault protection
4.4.1 Generator stator earth fault
protection
With the generator neutral point earthed earthed as
shown in Figure 4.7 the MRI3 picks up only to phase
earth faults between the generator and the location of
the current transformers supplying the relay.
Earth faults beyond the current transformers, i.e. on the
consumer or line side, will not be detected.
Figure 4.7: Generator stator earth fault protection
4.4.2 System earth fault protection
With the generator neutral point earthed as shown in
Figure 4.8, the MRI3 picks up only to earth faults in
the power system connected to the generator. It does
not pick up to earth faults on the generator terminals or
in generator stator.
Figure 4.8: System earth fault protection
TD_ MRI3_ 11.07_ GB 17
4.5 Earth-fault directional feature
( ER/ XR-relay type)
A built-in earth-fault directional element is available for
applications to power networks with isolated or with
arc suppressing coil compensated neutral point.
For earth-fault direction detection it is mainly the question
to evaluate the power flow direction in zero sequence
system. Both the residual voltage and neutral
( residual) current on the protected line are evaluated to
ensure a correct direction decision.
In isolated or compensated systems, measurement of
reactive or active power is decisive for earth-fault detection.
It is therefore necessary to set the ER/ XR-relay
type to measure according to sin or cos methods,
depending on the neutral-point connection method.
The residual voltage UE required for determining earth
fault direction can be measured in three different
ways, depending on the voltage transformer connections.
( refer to Table 4.1) . Total current can be measured by
connecting the unit either to a ring core C.T. or to current
transformers in a Holmgreen circuit. However,
maximum sensitivity is achieved if the MRl1 protective
device is connected to a ring core C. T. ( see Figure
3.2) .
The pick-up values IE> and IE> > ( active or reactive current
component for cos or sin method) for ER-relay
types can be adjusted from 0.01 to 0.45 x IN. For relay
type MRI3-XR these pick-up values can be adjusted
from 0.1 to 4.5% IN.
Adjustment
possibility
Application Voltage transformer
connections
Measurd
voltage at
earth fault
Correction factor
for residual
voltage
3pha
3-phase voltage
transformer connected
to terminals A3, A5,
A7, A2
( MRI3-IRER;
MRI3-IER;
MRI3-ER/ XR)
 3 x UN = 3 x U1N K = 1 / 3
e-n
e-n winding
connected to
terminals A3, A2
( MRI3-IER;
MRI3-ER/ XR)
UN =  3 x U1N K = 1 /  3
1: 1
Neutral-point voltage
( = residual voltage)
terminals A3, A2
( MRI3-IER;
MRI3-ER/ XR)
U1N = UNE K = 1
Table 4.1: Connection of the voltage transformers
18 TD_ MRI3_ 11.07_ GB
Figure 4.9: Phase position between the residual voltage and zero sequence current for faulted and non-faulted lines in case of isolated
systems ( sin )
UE - residual voltage
IE - zero sequence current
IC - capacitive component of zero sequence current
IW - resistive component of zero sequence current
By calculating the reactive current component ( sin
adjustment) and then comparing the phase angle in
relation to the residual voltage UE, the ER/ XR-relay
type determines whether the line to be protected is
earth-faulted.
On non-earth-faulted lines, the capacitive component
Ic( a) of the total current precedes the residual
voltage by an angle of 90 . In case of a faulty line
the capacity current IC( b) lags behind the residual
voltage at 90 .
Figure 4.10: Phase position between the residual voltage and zero sequence current for faulted and non-faulted lines in case of
compensated systems ( cos )
UE - residual voltage
IE - zero sequence current
IL - inductive component of zero sequence current
( caused by Petersen coil)
IC - capacitive component of zero sequence current
IW - resistive component of zero sequence current
In compensated mains the earthfault direction cannot
be determined from the reactive current components
because the reactive part of the earth current depends
upon the compensation level of the mains. The ohmic
component of the total current ( calculated by cos adjustment)
is used in order to determine the direction.
The resistive component in the non-faulted line is in
phase with the residual voltage, while the resistive
component in the faulted line is opposite in phase with
the residual voltage.
By means of an efficient digital filter harmonics and
fault transients in the fault current are suppressed. Thus,
the uneven harmonics which, for instance, are caused
an electric arc fault, do not impair the protective function.
19 TB MRI1 09.98 E
4.6 Determining earth short-circuit
fault direction
The SR-relay type is used in solidly-earthed or resistance-
earthed systems for determining earth short-circuit
fault direction. The measuring principle for determining
the direction is based on phase angle measurement
and therefore also on the coincidence-time measurement
between earth current and zero sequence voltage.
The zero sequence voltage U0 required for determining
the earth short-circuit fault direction is generated internally
in the secondary circuit of the voltage transformers.
With SR/ ISR-relay types the zero sequence voltage U0
can be measured directly at the open delta winding
( e-n) . Connection A3/ A2.
4.6.1 Directly earthed system
Most faults in a characteristic angle are predominantly
inductive in character. The characteristic angle between
current and voltage at which the greatest measuring
sensitivity is achieved has therefore been selected
to precede zero sequence voltage U0 by 110 .
Figure 4.11: Characteristic angle in solidly earthed-systems ( SOLI)
4.6.2 Resistance earthed system
Most faults in a resistance-earthed system are predominantly
ohmic in character, with a small inductive
part. The characteristic angle for these types of system
has therefore been set at + 170 in relation to the zero
sequence voltage U0 ( see Figure 4.12) .
Figure 4.12: Characteristic angle in resistance-earthed systems
( RESI)
The pickup range of the directional element is set by
turning the current indicator at the characteristic angle
through + 90 , to ensure reliable determination of the
direction.
Figure 4.13: Adjustable characteristical angle of 45 to 309
For all other applications the characteristical angle between
45 and 309 is free selectable
20 TD_ MRI3_ 11.07_ GB
4.6.3 Connection possibilities of the voltage
transformers for SR relay types
Application Voltage transformer
connections
3-phase voltage
transformer connected
to terminals
A3, A5, A7, A2
( MRI3-IRSR;
MRI3-ISR;
MRI3-SR)
e-n winding
connected to
terminals A3, A2
( MRI3-ISR;
MRI3-SR)
Neutral-point voltage
( = residual voltage)
terminals A3, A2
( MRI3-ISR;
MRI3-SR)
4.7 Demand imposed on the main
current transformers
The current transformers have to be rated in such a
way, that a saturation should not occur within the following
operating current ranges:
Independent time overcurrent
function: K1 = 2
Inverse time overcurrent function: K1 = 20
High-set function: K1 = 1.2 - 1.5
K1 = Current factor related to set value
Moreover, the current transformers have to be rated
according to the maximum expected short circuit current
in the network or in the protected objects.
The low power consumption in the current circuit of
MRI3, namely , IE>
Measuring range overflow max. L1, L2, L3, E
Setting values:
phase ( I> ; CHAR I> ; tI> ; I> > ; tI> > )
earth ( IE> ; CHAR IE; tIE> ; IE> > ; tIE> > ; UE> )
Current settings
Trip delay
Characteristics

one time for each
parameter
I > ; CHAR I> ; tI> ; I> > ;
tI> > ; LED
IE> ; CHAR IE; tIE> ; IE> > ;
tIE> > ; UE>
Current display as second rated repetition
current Iprim ( phase) / Iprim ( earth)
SEC ( 0.001-50.0 kA prim) L1, L2, L3, E
Parameter switch/ external triggering of
the fault recorder
SET1, SET2, B_ S2, R_ S2,
B_ FR, R_ FR, S2_ FR
P2
LED blinking after activation FLSH, NOFL
Characteristics DEFT, NINV, VINV, EINV,
LINV, RINV
CHAR I>
Characteristics DEFT, NINV, VINV, EINV,
LINV, RINV, RXIDG
CHAR IE>
Reset setting ( only available at inverse
time characteristics)
0s / 60s

I> ; CHAR I> ; tI>
IE> ; CHAR IE> ; tIE>
Relay characteristic angle for pase current
directional feature
RCA in degree ( )

LED ( green)
Warning or Trip at earth fault
measuring ( E- and ER/ XR-types)
TRIP
WARN

IE>
Measured method of the residual
voltage UE 1)
3 PHA ; E-N ; 1: 1

UE>
residual voltage setting voltage in volts UE>
changeover of isolated ( sin )
or compensated ( cos )
networks ( for ER/ XR-type)
SIN
COS

Change over of solidly/ resistance
earthed networks ( SR-type)
SOLI
RESI

Switch failure protection tCBFP
Tripping protection
switch failure protection
CBFP After fault tripping
Nominal frequency f= 50 / f= 60
Blocking of function EXIT until max. setting value LED of blocked
parameter
Slave address of serial interface 1 - 32

RS
Baud-Rate 2) 1200-9600 RS
Parity-Check 2) even odd no RS
Recorded fault data Tripping currents and other
fault data

one time for each phase
L1, L2, L3, E
I> , I> > , IE> , IE> > , UE>
Save parameter? SAV?
Delete failure memory wait
Enquiry failure memory FLT1; FLT2..... L1, L2, L3, E
I> , I> > , IE> , IE> > ,
Trigger signal for the fault recorder TEST, P_ UP, A_ PI, TRIP FR
Number of fault occurences S = 2, S = 4, S = 8 FR
Display of date and time Y = 99, M = 10, D = 1,
h = 12, m = 2, s = 12

Change over the blocking function PR_ B, TR_ B und ;

I> , I> > , IE> , IE> > oder
tI> , tI> > , tIE> , tIE> >
1) refer to 4.4
2) only Modbus
22 TD_ MRI3_ 11.07_ GB
Function Display shows Pressed push button Corresponding LED
Blocking of the protection function BLOC, NO_ B I> , I> > , IE> , IE> >
Save parameter! SAV! for about 3 s
Software version First part ( e.g. D01-)
Sec. part ( e.g. 8.00)

one time for each part
Manual trip TRI? three times
Inquire password PSW?
Relay tripped TRIP
or after fault tripping
Secret password input XXXX

System reset SEG
for about 3 s
Table 5.1: possible indication messages on the display
1) refer to 4.4
2) only Modbus
TD_ MRI3_ 11.07_ GB 23
5.2 Setting procedure
After push button has been pressed,
always the next measuring value is indicated. Firstly
the operating measuring values are indicated and then
the setting parameters. By pressing the push
button the setting values can directly be called up and
changed. Before parameter setting can be started the
relevant password must be entered ( refer to chapter
4.4 of the " MR Digital Multifunctional Relay" description) .
5.3 System parameter
5.3.1 Display of measuring values as
primary quantities ( Iprim phase)
With this parameter it is possible to show the indication
as primary measuring value. For this purpose the
parameter must be set to be equal with the rated primary
CT current. If the parameter is set to " SEK" , the
measuring value is shown as a multiple of the rated
secondary CT current.
Example:
The current transformer used is of 1500/ 5 A. The
flowing current is 1380 A. The parameter is set to
1500 A and on the display " 1380 A" are shown. If
the parameter is set to " SEK" , the value shown on the
display is " 0.92" x In.
Note:
The pick-up value is set to a multiple of the rated secondary
CT current.
5.3.2 Display of earth current as primary
quantity ( Iprim earth)
The parameter of this function is to be set in the same
way as that described under 5.3.1. If the parameter is
not set to " SEK" , to relay types MRI3-X and MRI3-XR it
applies too, that the measuring value is shown as primary
current in ampere. Apart from that the indication
refers to % of IN.
5.3.3 Display of residual voltage UE
as primary quantity ( Uprim/ Usec)
The residual voltage can be shown as primary measuring
value. For this parameter the transformation ratio of
the VT has to be set accordingly. If the parameter is
set to " SEK" , the measuring value is shown as rated
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.
5.3.4 Voltage transformer connection for
residual voltage measuring
( 3pha/ e-n/ 1: 1)
Depending on the connection of the voltage transformer
of ER/ XR-relay types three possibilities of the
residual voltage measurement can be chosen
( see chapter 4.5) .
5.3.5 Nominal frequency
The adapted FFT-algorithm requires the nominal frequency
as a parameter for correct digital sampling
and filtering of the input currents.
By pressing the display shows " f= 50" or
" f= 60" . The desired nominal frequency can be adjusted
by or and then stored with .
5.3.6 Display of the activation storage
( FLSH/ NOFL)
If after an activation the existing current drops again
below the pickup value, e.g. I> , without a trip has
been initiated, LED I> signals that an activation has
occurred by flashing fast. The LED keeps flashing until
it is reset again ( push button ) . Flashing can
be suppressed when the parameter is set to NOFL.
24 TD_ MRI3_ 11.07_ GB
5.3.7 Parameter switch/ external
triggering of the fault recorder
By means of the parameter-change-over switches it is
possible to activate two different parameter sets.
Switching over of the parameter sets can either be
done by means of software or via the external inputs
RESET or blocking input. Alternatively, the external inputs
can be used for Reset or blocking of the triggering
of the fault recorder.
Softwareparameter
Blocking input
used as
RESET Input
use as
SET1 Blocking input RESET Input
SET2 Blocking input RESET Input
B_ S2 Parameter switch RESET Input
R_ S2 Blocking input Parameter
switch
B_ FR Ext. triggering of
the FR
Reset input
R_ FR Blocking input Ext. Trigger for
FR
S2_ FR Parameter switch Ext. Trigger for
FR
With the settings SET1 or SET2 the parameter set is
activated by software. Terminals C8/ D8 and D8/ E8
are then available as external reset input or blocking
input.
With the setting B_ S2 the blocking input ( D8, E8) is
used as parameter-set change-over switch. With the
setting R_ S2 the reset input ( D8, E8) is used as parameter-
set change-over switch. With the setting B_ FR
the fault recorder is activated immediately by using the
blocking input. On the front plate the LED FR will then
light up for the duration of the recording. With the setting
R_ FR the fault recorder is activated via the reset
input. With the setting S2_ FR parameter set 2 can be
activated via the blocking input and/ or the fault recorder
via the reset input.
The relevant function is then activated by applying the
auxiliary voltage to one of the external inputs.
Important note:
When functioning as parameter change over facility,
the external input RESET is not available for resetting.
When using the external input BLOCKING the protection
functions must be deactivated by software blocking
separately ( refer to chapter 5.7.1) .
5.4 Parameter protection
5.4.1 Pickup current for phase
overcurrent element ( I> )
The setting value for this parameter that appears on
the display is related to the nominal current ( IN) of the
relay. This means: pickup current ( Is) = displayed value
x nominal current ( IN) e.g. displayed value = 1.25
then, Is = 1.25 x IN.
5.4.2 Time current characteristics for
phase overcurrent element
( CHAR I> )
By setting this parameter, one of the following 6 messages
appears on the display:
DEFT - Definite Time
NINV - Normal Inverse
VINV - Very Inverse
EINV - Extremely Inverse
RINV - RI-Inverse
LINV - Long Time Inverse
Anyone of these four characteristics can be changed
by using -push buttons, and can be stored by
using -push button.
5.4.3 Trip delay or time factor for
phase overcurrent element ( tI> )
Usually, after the characteristic is changed, the time
delay or the time multiplier should be changed accordingly.
In order to avoid an unsuitable arrangement of
relay modes due to carelessness of the operator, the
following precautions are taken:
If, through a new setting, another relay characteristic
other than the old one has been chosen ( e.g. from
DEFT to NINV)