Woodward MRI3-ITE User manual

MRI3-ITE(R) – Time overcurrent relay with
thermal replica and earth current measuring
Manual MRI3-ITER (Revision A)

Woodward Manual MRI3-ITER GB
2 DOK-TD-MRI3 ITERE 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-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 3
Contents
1.Introduction and Application ......................................................................5
2.Features and characteristics ......................................................................6
3.Design...........................................................................................................7
3.1Connections ........................................................................................................................7
3.1.1Analogue input circuits ....................................................................................................8
3.1.2Output relays ...................................................................................................................9
3.2Relay output contacts..........................................................................................................9
3.2.1Blocking input ................................................................................................................10
3.2.2External reset input .......................................................................................................10
3.2.3Fault recorder ................................................................................................................10
3.3Front plate .........................................................................................................................12
4.Working principle.......................................................................................14
4.1Analog circuits ...................................................................................................................14
4.2Digital circuits ....................................................................................................................14
4.3Thermal replica..................................................................................................................15
4.3.1Definitions......................................................................................................................15
4.4Algorithm ...........................................................................................................................16
4.5Earth fault protection .........................................................................................................19
4.5.1Generator stator earth fault protection ..........................................................................19
4.5.2System earth fault protection ........................................................................................19
4.6Earth-fault directional feature (ER-relay type)...................................................................20
4.7Demand imposed on the main current transformers.........................................................22
5.Operation and settings..............................................................................23
5.1Display...............................................................................................................................23
5.1.1LEDs..............................................................................................................................25
5.2Setting procedure..............................................................................................................27
5.3System parameter.............................................................................................................27
5.3.1Display of measuring values as primary quantities (Iprim phase)...................................27
5.3.2Display of earth current as primary quantity (Iprim earth) ...............................................27
5.3.3Display of residual voltage UE as primary quantity (Uprim/Usec).....................................27
5.3.4Voltage transformer connection for residual voltage measuring (3pha/e-n/1:1)...........27
5.3.5Nominal frequency ........................................................................................................28
5.3.6Display of the activation storage (FLSH/NOFL)............................................................28
5.3.7Parameter switch/external triggering of the fault recorder ............................................28
5.4Protection parameters.......................................................................................................29
5.4.1Pickup value of the thermal overload protection IB,A and IB,T ........................................29
5.4.2Constant k .....................................................................................................................29
5.4.3Energizing delay (time) for the thermal overload ..........................................................29
5.4.4Time constant .............................................................................................................29
5.4.5Pickup current for phase over current element (I>) ......................................................29
5.4.6Time current characteristics for phase overcurrent element (CHAR I>).......................30
5.4.7Trip delay or time multiplier for phase over current element (tI>) .................................30
5.4.8Reset setting for inverse time tripping characteristics in the phase current path .........30
5.4.9Current setting for high set element (I>>) .....................................................................30
5.4.10Trip delay for high set element (tI>>) ........................................................................30
5.4.11Pickup value for residual voltage UE(ITER-relay type).............................................31
5.4.12Pickup current for earth fault element (IE>)................................................................31
5.4.13WARN/TRIP changeover ..........................................................................................31
5.4.14Time current characteristics for earth fault element (CHAR IE) (not ER device type) ... 31
5.4.15Trip delay or time multiplier for earth fault element (tIE>)...........................................31
5.4.16Resetting time for inverse time earth fault element (not ER-relay type) ...................31
5.4.17Current setting for high set element of earth fault supervision (IE>>)........................31
5.4.18Trip delay for high set element of earth fault supervision (tIE>>)................................32
5.4.19COS/SIN Measurement (ER - relay type) .................................................................32
5.4.20Block/Trip – time (only ITE-device type) ...................................................................32
5.4.21Circuit breaker failure protection tCBFP .......................................................................32
5.4.22Adjustment of the slave address ...............................................................................32

Woodward Manual MRI3-ITER GB
4 DOK-TD-MRI3 ITERE Rev.A
5.4.23Setting of Baud-rate (applies for Modbus Protocol only).......................................... 32
5.4.24Setting of parity (applies for Modbus Protocol only)................................................. 32
5.5Fault recorder ................................................................................................................... 33
5.5.1Adjustment of the fault recorder ................................................................................... 33
5.5.2Number of the fault recordings ..................................................................................... 33
5.5.3Adjustment of trigger occurrences................................................................................ 33
5.5.4Pre-trigger time (Tpre) .................................................................................................... 33
5.6Adjustment of the clock..................................................................................................... 33
5.7Additional functions........................................................................................................... 34
5.7.1Blocking of the protective functions .............................................................................. 34
5.8Indication of measuring and fault values .......................................................................... 37
5.8.1Indication of measuring values ..................................................................................... 37
5.8.2Unit of the measuring values displayed........................................................................ 37
5.8.3Indication of fault data................................................................................................... 38
5.8.4Fault memory................................................................................................................ 38
5.9Reset................................................................................................................................. 39
5.9.1Erasure of fault storage ................................................................................................ 39
5.9.2Reset of the thermal replica register............................................................................. 39
6.Relay testing and commissioning............................................................40
6.1Power-On.......................................................................................................................... 40
6.2Testing the output relays and LEDs ................................................................................. 40
6.3Checking the set values.................................................................................................... 40
6.4Secondary injection test.................................................................................................... 40
6.4.1Test equipment ............................................................................................................. 40
6.4.2Example of test circuit for MRI3-ITE............................................................................. 41
6.4.3Checking the input circuits and measured values ........................................................ 41
6.4.4Example of a test circuit with earth fault directional feature ......................................... 42
6.4.5Checking the operating and resetting values of the relay ............................................ 43
6.4.6Checking the relay operating time ................................................................................ 43
6.4.7Checking the high set element of the relay .................................................................. 43
6.4.8Checking the external blocking and reset functions ..................................................... 43
6.4.9Testing the external blocking with Block/Trip function.................................................. 44
6.4.10Test of the CB failure protection ............................................................................... 44
6.5Primary injection test ........................................................................................................ 44
6.6Maintenance ..................................................................................................................... 45
7.Technical data............................................................................................46
7.1Measuring circuits............................................................................................................. 46
7.2Common data ................................................................................................................... 46
7.3Setting ranges and steps .................................................................................................. 47
7.3.1Systemparameter ......................................................................................................... 47
7.3.2Overload protection ...................................................................................................... 48
7.3.3Over current time protection ......................................................................................... 49
7.3.4Earth fault protection..................................................................................................... 50
7.3.5Earth fault protection (ER-Type)................................................................................... 50
7.3.6Determination of earth fault direction (MRl3-ITER) ...................................................... 51
7.3.7BlockTrip – time** ......................................................................................................... 51
7.3.8Switch failure protection................................................................................................ 51
7.3.9Interface parameter ...................................................................................................... 51
7.3.10Parameter for the fault recorder................................................................................ 51
7.4Tripping characteristics..................................................................................................... 52
7.4.1Thermal characteristic .................................................................................................. 52
7.4.2Preload factor ............................................................................................................... 53
7.4.3Inverse time over current protection relay .................................................................... 54
7.5Tripping characteristics..................................................................................................... 55
7.6Output relays .................................................................................................................... 58
8.Order form..................................................................................................59

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 5
1.Introduction and Application
The digital multifunctional relay MRI3-ITE(R) has been designed as a universal time over current
protection relay with thermal replica for generators, transformers and cables.
The relay gives a complete thermal characteristic of the electrical equipment to be protected taking
into account its initial load.
The MRI3-ITE(R) furthermore provides a universal time over current and earth fault protection with
the following functions:
Integrated determination of earth fault direction for application to power system networks
with isolated or arc suppressing coil (Peterson coil) neutral earthing (ER-relay type),
independent (Definite) time over current relay.
inverse time over current relay with selectable characteristics,
two-element (low and high set) earth fault protection with definite or inverse time
characteristics.

Woodward Manual MRI3-ITER GB
6 DOK-TD-MRI3 ITERE Rev.A
2.Features and characteristics
Microprocessor technology with self-supervision,
measuring of phase current as RMS value,
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
(earth current only),
in accordance with the requirements as per IEC 255-8, VDE 435 part 3011 for overload
relays,
two parameter sets,
selectable protective functions between:
- definite time over current relay and
- inverse time over current 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 mode for inverse time characteristics selectable,
high set over current element with instantaneous trip,
two-element (inverse time and definite time) over current relay both for phase and earth
faults,
determination of earth short-circuit fault direction for systems with isolated or compensated
neutral point,
Display of measuring values as primary quantities,
measuring of phase current of the short circuit breaker operation,
blocking of high set element (e.g. for selective fault detection through minor over current
protection units after unsuccessful AR),
the protective functions can be freely assigned to the output relays (assignment matrix),
withdrawable modules with automatic short circuiters of C.T. inputs when modules are
with-drawn,
storage of trip values and switching-off time (tCBFP) of 5 fault occurrences (fail-safe of
voltage),
recording of up to eight fault occurrences with time stamp,
switch failure protection,
serial data exchange via RS485 interface possible; alternatively with SEG RS485 Pro-
Open Data Protocol or Modbus Protocol,
Display of date and time.
Important:
For additional common data of all MR-relays please refer to manual „MR-Digital Multifunctional re-
lays“.

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 7
3.Design
3.1 Connections
Figure 3.1: Connection diagram
Figure 3.2: 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.

Woodward Manual MRI3-ITER GB
8 DOK-TD-MRI3 ITERE Rev.A
Figure 3.3: 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 3.2 and Figure 3.3.
Voltage measuring for the directional detection:
Figure 3.4: Measuring of the phase voltages for the directional detection at earth-fault protection (IE> and IE>>).
3.1.1 Analogue input circuits
The protection unit receives the analogue input signals of the phase currents IL1 (B3-B4), IL2 (B5-
B6), IL3 (B7-B8) and the residual current IE(B1-B2) each via separate input transformers. The con-
stantly detected current measuring values are galvanically decoupled, filtered and finally fed to the
analogue/digital converter.

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 9
3.1.2 Output relays
Two relays are equipped with two change-over contacts and three relays with each one change-
over contact for alarm. Apart from the relay for self-supervision, all protective functions can be op-
tionally 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.
3.2 Relay output contacts
Figure 3.5: Relay outputs

Woodward Manual MRI3-ITER GB
10 DOK-TD-MRI3 ITERE Rev.A
3.2.1 Blocking input
The function for blocking can be parameterized arbitrary. When an auxiliary voltage is connected to
D8/E8 those relay functions will be blocked which were parameterized before (see chapter 5.7.1).
3.2.2 External reset input
See chapter 5.9
3.2.3 Fault recorder
The MRI3-ITER has a fault value recorder which records the measured analogue values as
instantaneous values. The instantaneous values
i
L1, iL2, iL3, iE,
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 16 s (with 50 Hz) and
13.33 s (with 60 Hz) per channel.
Storage division
Independent of the recording time, the entire storage capacity can be divided into several cases of
disturbance with a shorter recording time each. In addition, the deletion behavior of the fault
recorder can be influenced.
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 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 re-
cords can be stored (written over).
Memory space 6 to 4 is occupied.
Memory space 5 is currently being written in
Figure 3.6: Division of the memory into 8 segments, for exam-ple
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.

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 11
Figure 3.7: 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 with HTL/PL-Soft4.
The data is graphically edited and displayed. Bi-nary tracks are recorded as well, e.g. activation
and trip.

Woodward Manual MRI3-ITER GB
12 DOK-TD-MRI3 ITERE Rev.A
3.3 Front plate
Figure 3.8: Front plate MRI3-ITE
Figure 3.9: Front plate MRI3-ITER

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 13
The LED RS, Aand Tyellow light up yellow (MRI3-ITE)
The LED RS, IP and IQ light up yellow (MRI3-ITER).
All other LEDs are two-colored. LEDs left to the alphanumerical display light-up green during mea-
suring and red at alarm.
LEDs underneath the pushbutton <SELECT/RESET> light-up green during setting and inquiry of
the setting values printed left to the LEDs. They light-up red when the setting values printed at the
right to the LEDs are activated.
The LED labeled with the letters LR is a light while the fault recorder is being adjusted.

Woodward Manual MRI3-ITER GB
14 DOK-TD-MRI3 ITERE Rev.A
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 suppressed by an analogue RC 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 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.
4.2 Digital circuits
The essential part of the MRI3-ITE relay is a powerful microcontroller. All of the operations, from
the analogue digital conversion to the relay trip decision, are carried out by the microcontroller digi-
tally. 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 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 suppress high frequency harmonics
and DC components caused by fault-induced transients or other system disturbances. The calcu-
lated actual current values are compared with the relay settings.
In case, the time for which a current was above the preset pickup value, exceeds the trip delay or
the thermal capacity is reached, an alarm signal will be given. Dependent on their adjustment the
output relays will also be 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 micro-processor is supervised by a built-in
"watchdog" timer. In case of a failure the watchdog timer re-sets the microprocessor and gives an
alarm signal, via the output relay "self supervision".
Figure 4.1: Block diagram

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 15
4.3 Thermal replica
4.3.1 Definitions
Basic current IB:
Set limiting value of the overload current at which the relay must not trip. This, in general, is the
maximally permissible operating current in consideration of additional influencing quantities on the
heating (e.g. heat dissipation by transformer oil or air convection).
The settings of the overload characteristics refer to this basic current.
Time constant k:
Constant to be multiplied by the basic current in order to determine the current that may be higher
than IB.
Instruction for motor protection: k = 1...1.2
MRI3-ITE(R) default value: k = 0.5
Remark:
For the calculation of the temperature equivalent, only the basic current has to be taken into ac-
count: IB2 ~ .
The constant k is used to determine the pickup value
(IBk) and to calculate the temperature according to which the object to be protected reaches its
tripping value after expiry of a long time (Trip = k2 100%).
Adjustment of the nominal current with IB(e.g. 1 IN) and selection of an overload factor k
(e.g. 1.2). From this, a pickup value of 1.2 INand a tripping value of 144% will result.
Thermal time constant :
It indicates the time until the temperature of the electrical equipment to be protected reaches 63%
of the stationary operating temperature. (data sheet of the electrical equipment or practical
values). Thumb rule: With the current I being constant, approx. 63% of the maximal temperature
will be reached when t =. After expiry of a time t = 5 the maximal temperature is almost reached
(99%).
The time constant for warming up and that for cooling down may be different!
Tripping characteristic with preload:
Characteristic with complete memory function, taking into account the thermal effect of the current
before occurrence of the overload in the thermal replica of the electrical item to be protected.
Figure 4.2: Thermal time constant 

Woodward Manual MRI3-ITER GB
16 DOK-TD-MRI3 ITERE Rev.A
4.4 Algorithm
Based on the defined thermal model, one can de-duce that an energy Q is stored in the electrical
equipment.
After expiry of a long time and with a constant cur-rent load, a stationary condition will be achieved
in which the temperature of the electrical equipment does not increase anymore. The heat supplied
for a unit of time is equal to that released by cooling down (steady energy balance).
Q
released = Qsupplied
The supplied thermal energy as well as the temperature of the electrical equipment in stationary
condition are in proportion to the square of the phase current (e.g. ohmic losses and iron losses in
the transformer).
Q I² or I²
Since the pickup value in the MRI3-ITE is deter-mined by IB, the following relation is effective:
n k² (IBk)²
For this purpose, the temperature T that really prevails in the electrical equipment needs to be
known. This temperature (in%) is described in the thermal replica through the temperature equiv-
alent k IB. When being loaded with the maximum permissible operating current B in stationary
condition, the electrical equipment reaches the maximum allowed operating temperature B. For
this load, the temperature equivalent is defined as k2100%.
󰇛%󰇜I
󰇛KlB󰇜·100%
I.e.: At a load with I = 0.9 x (k IB) and k IB= 1.2, and according to the before indicated definition,
the temperature reaches 81% of the maximum permissible operating temperature. For an
electrical equipment that - after initial load - will be loaded beyond the admissible operating current
(I > k•IB), the following temperature curve will result:
Figure 4.3: Warming up of an electrical item

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 17
The thermal equivalent ( T = ) is described by an exponential function.
for (> 0):
(t‘)= 0+(max - 0) (1-󰆓
)
after transposition:
(t)= max+(0 - max)·󰆓

If (t’)k2·100% the alarm or trip element is activated.
The temperature after dt can be calculated as follows:
1=max+(0- max) · 

After 2 times dt:
2=max+(0-max)·

or
2=max+(1-max) · 

general:
n=max+(n-1-max) · 

Thus, a recursion formula was established from which in order to calculate the thermal equivalent
n:
The last value n-1,
the stationary final value max for the actual current,
the adjusted time constant ,
and the time since the last calculation dt must be known.
Analogous, for the temperature equivalent with max the following formula is applied:
󰇛t󰆒󰇜I
󰇛k·IB󰇜·100%󰇧I 󰇛k·lB󰇜·100%󰇨·e󰆒

with I = highest measured phase current.
In each new calculation step n, the momentary temperature equivalent is determined as follows:

󰇛·󰇜·100%󰇧 I 󰇛k·IB󰇜·100%󰇨·

with In: Highest measured phase current in
calculation step n
dt: Time interval between the individual
calculation steps
n-1: Temperature equivalent of the
preceding calculation step

Woodward Manual MRI3-ITER GB
18 DOK-TD-MRI3 ITERE Rev.A
The temperature equivalent n-1 has not been calculated after start of the protection program (con-
nection of auxiliary voltage), therefore, the temperature state of the electrical item to be protected is
expected to be cold.
If, however, the electrical equipment has been initially loaded, it will take approximately 3 x
warming up, (at constant load) until the thermal equivalent equals the real state.
Different time constants:
After switching off the electrical equipment (In = 0) temperature will decrease and tend towards n
= 0 (environmental temperature).
e.g.: cooling down = 2 warming up
Depending on the comparison between the last measured current and the actual current the
cooling down or warming up constant will be applied for calculation.
In In-1 warming up
In < In-1 cooling down
If the relay is supplied by the mains to be protected, i.e. if the relay is not supplied to auxiliary vol-
tage after tripping of the mains c.b., the following has to be considered:
After return of the supply voltage, it is assumed that the electric item is in cold condition. In this
case this assumption does not comply with the reality. Therefore an external supply voltage should
be applied.
The tripping criterion for the alarm or tripping element of the thermal characteristic is:
Trip > k2·100%
The effective values of the measured phase currents are detected by calculating the root out of the
integral of a period’s momentary current squares. Calculation of the thermal equivalent is always
based on the highest of the three phase currents.

Manual MRI3-ITER GB Woodward
DOK-TD-MRI3 ITERE Rev.A 19
4.5 Earth fault protection
4.5.1 Generator stator earth fault protection
With the generator neutral point earthed as shown in Figure 4.4 the MRI3-ITER 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 4.4: Generator stator earth fault protection
4.5.2 System earth fault protection
With the generator neutral point earthed as shown in Figure 4.5, the MRI3-ITER 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 4.5: System earth fault protection

Woodward Manual MRI3-ITER GB
20 DOK-TD-MRI3 ITERE Rev.A
4.6 Earth-fault directional feature (ER-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 relay to measure according to sin or cos me-
thods, 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 trans-formers in a Holmgreen circuit. However, maximum sensitivity is achieved if the
MRI3-ITER protective device is connected to a ring core C. T. (see Figure 3.3).
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.
Adjustment
possibility Application Voltage transformer connections Measured voltage at
earth fault
Correction
factor for
residual
voltage
„3pha“
3-phase voltage
transformer con-
nected to terminals
A3, A5, A7, A2 3 x UN= 3 x
U1N
K = 1 / 3
„e-n“
e-n winding
connected to
terminals A3, A2
UN= 3 x U1N K = 1 / 3
„1:1“
Neutral-point voltage
(= residual voltage)
terminals A3, A2
U1N = UNE K = 1
Table 4.1: Connection of voltage transformers