ABB Substation Automation Products and Systems
1MRS750616-MUM
Issued: 07.07.99
Version: A
Checked: H.S.
Approved: L.N.
REJ 527
Directional or Non-Directional
Earth-Fault Relay
Technical Reference Manual
Data subject to change without prior notice
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Contents
1. Introduction ...........................................................................................5
1.1. About this manual .........................................................................5
1.2. The use of the relay ......................................................................5
1.3. Features ........................................................................................5
1.4. Guarantee .....................................................................................6
2. Safety information .................................................................................7
3. Instructions ...........................................................................................8
3.1. Application .....................................................................................8
3.2. Requirements ................................................................................8
3.3. Configuration .................................................................................9
4. Technical description ..........................................................................10
4.1. Functional description .................................................................10
4.1.1. Product functions ................................................................10
4.1.1.1. Schema of product functions .......................................10
4.1.1.2. Earth-fault current, zero-sequence voltage and
intermittent earth-faults ................................................10
4.1.1.3. Inputs ...........................................................................11
4.1.1.4. Outputs ........................................................................11
4.1.1.5. Circuit-breaker failure protection .................................11
4.1.1.6. Disturbance recorder ...................................................11
4.1.1.7. MMI module .................................................................11
4.1.1.8. Self-supervision ...........................................................12
4.1.2. Configuration ......................................................................12
4.1.3. Protection ............................................................................13
4.1.3.1. Block diagram ..............................................................13
4.1.3.2. Directional or non-directional earth-fault current unit ..13
4.1.3.3. Zero-sequence voltage unit .........................................17
4.1.3.4. Protection against intermittent earth-faults ..................18
4.1.3.5. Time/current characteristics ........................................19
4.1.3.6. Settings .......................................................................23
4.1.3.7. Technical data of protection functions .........................31
4.1.4. Monitoring ...........................................................................33
4.1.5. Self-supervision (IRF) .........................................................33
4.1.6. I/O test ................................................................................34
4.1.7. Disturbance recorder ..........................................................34
4.1.7.1. Function .......................................................................34
4.1.7.2. Recorder data ..............................................................34
4.1.7.3. Control and indication of recorder status .....................34
4.1.7.4. Triggering ....................................................................35
4.1.7.5. Settings and unloading ................................................35
4.1.7.6. Event code ..................................................................36
4.1.8. Recorded data ....................................................................36
4.1.9. External serial communication ............................................37
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4.1.9.1. Communication ports ..................................................37
4.1.9.2. Event codes ................................................................38
4.1.9.3. Remote transfer data ..................................................40
4.1.10.Relay parameterization ......................................................48
4.2. Design description ......................................................................48
4.2.1. Input / output connections ..................................................48
4.2.2. Serial communication connections .....................................51
4.2.3. Technical data ....................................................................52
5. Ordering information ..........................................................................58
6. References .........................................................................................59
7. Index ..................................................................................................60
8. Glossary .............................................................................................62
9. Check lists ..........................................................................................63
10.Customer feedback ............................................................................66
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1. Introduction
1.1. About this manual
This manual is intended to provide the user with thorough information on the relay
REJ 527 and its applications. The focus in the manual is on technical description of
the relay.
Instructions for using the Man-Machine Interface (MMI) are found in separate
“Operator’s Manual” and for installation in “Installation Manual”.
1.2. The use of the relay
The directional or non-directional earth-fault relay REJ 527 is intended to be used
for earth-fault protection and supervision in distribution substations. It can also be
used for protection of generators, motors and transformers. Generally the relay
measures the zero-sequence voltage, earth-fault current and phase angle of the
system.
The protection relay REJ 527 is based on a microprocessor environment. A self-
supervision system monitors continuously the operation of the relay.
The MMI includes an LCD display which makes the local use of the relay safe and
easy.
Local control of the protection relay can be carried out with a portable computer
connected to the front connector and remote control via the rear connector connected
to the distribution automation system through the serial interface and fibre-optic bus.
1.3. Features
• Directional or non-directional low-set earth-fault current stage I
0
> with definite-
time or inverse definite minimum time (IDMT) characteristic
• Directional or non-directional high-set earth-fault current stage I
0
>> with
definite-time characteristic
• Deblocking zero-sequence voltage stage U
0b
>
• The two earth-fault current stages configurable to operate alternatively as two
voltage stages: a three-stage voltage monitoring operation possible
• Intermittent earth-fault protection
• Circuit-breaker failure protection (CBFP)
• Disturbance recorder
• Two accurate measuring inputs
• Galvanically isolated binary input with a wide input voltage range
• All settings can be modified with a personal computer
• Settings are stored into non-volatile memory and remain even in case of power
supply failure
• Two normally open power output contacts
• Two change-over type signal output contacts
• Output contact functions freely configurable for desired operation
• Optical PC-connector for two-way data communication (front)
• RS-485 connector (rear) for system communication
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• Continuous self-supervision of hardware and software. At a permanent fault all
stages and outputs are blocked.
• Rated frequency user-selectable 50/60 Hz
• MMI with an alphanumeric LCD and manoeuvring buttons
• User-selectable password protection for MMI
• Display of primary current and voltage values as well as phase angle values
1.4. Guarantee
Please inquire the guarantee of your nearest ABB representative.
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2. Safety information
Dangerous voltages can occur on the connectors, even though the auxiliary voltage
is disconnected.
National and local electrical safety regulations must always be followed.
The frame of the protection relay has to be carefully earthed.
Current transformer has to be short-circuited before disconnecting the relay from it.
Only a competent electrician is allowed to carry out the electrical installation.
!
!
!
!
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3. Instructions
3.1. Application
The directional earth-fault relay REJ 527 is a secondary relay that is connected to
the voltage and current transformers of an object to be protected. It is designed for
earth-fault protection and supervision of distribution substations. Other application
areas are protection of generators, motors and transformers.
The relay comprises a zero-sequence voltage unit and an earth-fault current unit. The
voltage unit includes a low-set stage U
0b
> whereas the earth-fault current unit has
two stages, a low-set I
0
> and a high-set I
0
>> stage. The earth-fault current unit may
also be programmed to operate as voltage stages, a low-set U
0
> and a high-set U
0
>>
stage.
The earth-fault current and zero-sequence voltage stages of the relay continuously
measure the zero-sequence voltage, earth-fault current and phase angle of the
system. On detection of a fault the relay starts, trips the circuit breaker, provides
alarms, records fault data etc., in accordance with the application and the configured
relay functions.
The low-set earth-fault current stage can be given a definite-time or an inverse-time
characteristic whereas the high-set earth-fault current stage and the voltage stage
feature the definite-time characteristic alone. The operation of the earth-fault current
and voltage stages can be blocked by means of an external control signal.
The protection functions are independent of each other and have their own setting
groups and data recording. The voltage and current functions use conventional
transformer measurement.
Output contact matrix allows any start or trip signal from the protection stages to be
routed to the desired output contact.
3.2. Requirements
When the protection relay is operating under conditions specified below (see also
“Technical data”), the relay is practically maintenance-free. The relay includes no
parts or components subject to abnormal physical or electrical wear under normal
operating conditions.
Environmental conditions
• Specified ambient service temperature range -10...+55 °C
• Temperature influence on the operating values of the relay
within the specified ambient service temperature range 0.1% / °C
• Transport and storage temperature range -40...+70 °C
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3.3. Configuration
Setting and connection example
The appropriate configuration of the output contact matrix enables using the start
signals of the earth-fault current and voltage units as contact functions. The start
signals can be used for blocking co-operating protection relays, for signalling and
for initiating autoreclosing.
Fig. 3.3.-1 represents the relay with the default configuration: all trips are routed to
operate the circuit breaker.
Fig. 3.3.-1 Connection diagram of the directional earth-fault relay
L1
L2
L3
Optical
PC-interface
PC
Spa Bus
100V
1 A
0.2 A
PO1
IO
PO2
+ +
IRF
+
+
-
-
+
+
BI
REJ 527
0
I
IRF
+ -
U
aux
I/O
START
TRIP
START
TRIP
1
2
3
SGB1
SGB1
SGB1
INDICATORS RESET
RELAYS RESET
MEMORIZED VALUES RESET
∼
∼
Io>>
SGR1
SGR2
SGR3
SGR4
X
3
X
3
2
X
2
X
1
X
1
X
X
4
X
4
X
4
X
3
2
X
1
X
SGR5
SGR6
START
TRIP
5 6
3 4
13 14 15
1 2
17 18
1 2 3 4 6
SGB1
SGB1
SGB1
5
6
7
Blocking of stage Io>>
Blocking of stage Io>
Blocking of stage Uob>
10 11 12
7 8 9
SO1
X2.1
X2.1
X2.1
SO2
X2.1
X2.1
X2.1
X2.1
X1.1
1MKC950001-1
RER 103
Tx
Rx
Io>
Uob>
P1
P2
S2
S1
A
N
da
dn
ConD527
X=Default value
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4. Technical description
4.1. Functional description
4.1.1. Product functions
4.1.1.1. Schema of product functions
Fig. 4.1.1.1.-1 Product functions
4.1.1.2. Earth-fault current, zero-sequence voltage and intermittent
earth-faults
Refer to sections:
• 4.1.3.2. Directional or non-directional earth-fault current unit
• 4.1.3.3. Zero-sequence voltage unit
• 4.1.3.4. Protection against intermittent earth-faults
50 N
Io
PrF5_7
Uo
51 N
59 N
67 N
62 BF
EARTH-FAULT PROTECTION WITH
DEFINITE- OR INVERSE-TIME
CHARACTERISTIC, LOW-SET STAGE
EARTH-FAULT PROTECTION WITH
INSTANTANEOUS OR DEFINITE-TIME
CHARACTERISTIC, HIGH-SET STAGE
PO1
PO2
SO1
SO2
IRF
ZERO-SEQUENCE VOLTAGE
ELEMENT
CIRCUIT-BREAKER FAILURE
PROTECTION
REMOTE RESET, REMOTE SETTING CONTROL OR
BLOCKING INPUT FOR THE DIFFERENT PROTECTION
STAGES
SERIAL COMMUNICATION
DIRECTIONAL EARTH-FAULT
ELEMENT
OPTICAL
PC-INTERFACE
BINARY INPUT BI
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4.1.1.3. Inputs
The relay includes two energizing inputs and one external binary input controlled by
an external voltage. The function of the binary input is determined with selector
switches of the protection relay.
For more details of the inputs, refer to section 4.2.1. Input / output connections and
tables 9, 32 and 36.
4.1.1.4. Outputs
The relay is provided with two power outputs (PO1 and PO2) and two signal outputs
(SO1 and SO2). Switchgroups SGR1...6 are used for routing the start and trip signals
of any protection stage to the desired signal or power output.
4.1.1.5. Circuit-breaker failure protection
The relay features a circuit-breaker failure protection (CBFP) unit. The CBFP unit
generates a trip signal via output PO2 after the set operate time 0.10 s...1.00 s if the
fault has not been cleared by that time.
Normally, the CBFP unit controls the upstream circuit breaker. It can also be used
for tripping via redundant trip circuits of the same circuit breaker if the circuit
breaker is provided with two trip coils. The circuit-breaker failure protection unit is
activated with a switch of switchgroup SGF.
4.1.1.6. Disturbance recorder
The relay includes an internal disturbance recorder, which records momentary
measured values, external BI signal and states of the internal protection stages. The
disturbance recorder can be set to be triggered on operation of stages or on an
external BI signal, either on the falling or rising trigger edge.
4.1.1.7. MMI module
The MMI of the relay is equipped with six push-buttons and an alphanumeric LCD
for 2 x 16 characters. The push-buttons are used for navigating in the menu structure
and for adjusting set values.
An MMI password protects all user-changeable values from being changed by an
unauthorised person. The default value for the MMI password is “999”. With the
default value the password is not active and it is not required for altering parameter
values. For further information, refer to “Operator’s Manual”.
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4.1.1.8. Self-supervision
The self-supervision system of the relay handles run-time fault situations and
informs the user about an existing fault. When the self-supervision system detects a
permanent internal relay fault, the ready indication LED starts blinking. At the same
time the IRF relay that is normally picked up drops off and a fault code appears on
the display. During an internal fault all other output contacts are blocked.
Fig. 4.1.1.8.-1 Internal fault
The fault code is a number that identifies the fault type. (For fault codes, refer to
section “Self-supervision, IRF” in “Operator’s Manual”.)
Fault codes can indicate:
• No response on output contact test.
• Faulty program memory, work memory or parameter memory.
• Internal reference voltage error.
4.1.2. Configuration
The figure below illustrates how the start, trip and binary input signals can be
configured so that the required protection functions are obtained.
Fig. 4.1.2.-1 Signal diagram of the directional earth-fault relay
The functions of the blocking and start signals are selected with the switches of
switchgroups SGF, SGB and SGR, found in the menu group “Settings” of the
protection relay. The functions of these switches are explained in detail in the
corresponding SG_ -tables.
Faultc
C
E
INTERNAL FAULT
FAULT CODE : 56
STARTREADY TRIP
+ ++
IRF
I/O
START
TRIP
START
TRIP
1
2
3
SGB1
SGB1
SGB1
INDICATORS RESET
RELAYS RESET
Io>>
SGR1
SGR2
SGR3
SGR4
3
3
3
3
2
2
2
2
1
1
1
1
4
4
4
4
4
4
3
3
2
2
1
1
SGR5
SGR6
START
TRIP
5 6
3 4
13 14 15
17 18
SGB1
SGB1
SGB1
5
6
7
Blocking of stage Io>>
Blocking of stage Io>
Blocking of stage Uob>
10 11 12
7 8 9
X2.1
Io>
Uob>
MEMORIZED VALUES RESET
SGF1...SGF5
Uo
Io
BI
IRF
SO2
SO1 PO2
PO1
SDiag5_7
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4.1.3. Protection
4.1.3.1. Block diagram
Fig. 4.1.3.1.-1 Block diagram of the directional earth-fault relay REJ 527
4.1.3.2. Directional or non-directional earth-fault current unit
The directional earth-fault current unit of the relay REJ 527 comprises two earth-
fault current stages, a low-set stage I
0
> and a high-set stage I
0
>> that can be
configured as either directional or non-directional. For the directional stages there
are two alternative operation characteristics: 1) directional earth-fault with basic
angle and 2) directional earth-fault with sin(ϕ) or cos(ϕ) characteristics.
1) The operation of the directional earth-fault unit with basic angle is based on
measuring the earth-fault current I
0
and the zero-sequence voltage U
0
and further the
phase angle ϕ between the voltage and current. The earth-fault stage starts if the
following three criteria are fulfilled at the same time:
• The earth-fault current I
0
exceeds the set starting level of the earth-fault stage.
The earth-fault unit has two earth-fault current stages I
0
> and I
0
>>.
• The zero-sequence voltage U
0
exceeds the set starting level. The unit has one
starting level, U
0b
>, serving both stages in deblocking mode.
• The phase angle ϕ between the voltage and current falls within the operation
sector ϕ ±∆ϕ.
The basic angle ϕ of the network is -90° for isolated neutral networks and 0° for
resonant earthed networks, earthed over an arc suppression coil (Petersen coil) with
or without a parallel resistor. The operation sector is selectable to ∆ϕ = ±80° or ±88°,
both with the addition of a wider operation sector.
SGF1/5
1
1
C
to>>
1
C
START
TRIP
Uob>
Io>
Io>>
tb>
to>
SGR2/x
SGR1/x
SGR5/x
SGR6/x
SGR4/x
SGR3/x
tb>
70 ms
to>,k
70 ms
to>>
60 ms
0.12 * Io>
1.5 * Io>
1.25 * Io>
2 * Io>>
SGF2/1
Io>>
60 ms
SGB1/1
SGB1/2
SGB1/3
SGB1/5
SGB1/6
SGB1/7
SGF2/3
SGF2/7
SGF3/1
SGF3/3
SGF2/8
SGB1/4
SGB1/8
Uob
Io
BI
Uob>
Uo>
Io>
Uo>>
BlDREJ5_7
&
&
&
0.50% x Un
0.48% x In
ϕb/Ιϕ
ϕ
0.1 ... 1s
SGF1/1
C
5 s
PO1
1
SO1
SO2
4
3
2
1
1
C
5 s
PO2
SGF1/2
&
RESET INDICATORS AND LATCHED OUTPUT RELAYS
RESET INDICATORS, LATCHED OUTPUT RELAYS AND REGISTERS
RESET INDICATORS
SETTINGS (Group 1 / Group 2)
BASIC ANGLE CONTROL or Iϕ characteristica (sin(ϕ) or cos(ϕ))
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When an earth-fault stage starts, a starting signal is generated and simultaneously the
display on the front panel indicates starting. If the above mentioned criteria are
fulfilled long enough to exceed the set operate time, the stage that started initiates a
tripping signal. At the same time the operation indicator on the front panel is lit. The
red operation indicator remains lit although the protection stage resets. The direction
towards the fault spot is determined by means of the angle between the voltage and
current. The basic angle ϕ
b
can be set between -90° and 0°. When the basic angle ϕ
b
is 0°, the negative quadrant of the operation sector can be extended with ϕ
a
. (See Fig.
4.1.3.2.-1) The wider operation sector ϕ
a
is settable to 0...90°.
In Fig. 4.1.3.2.-1 ... Fig. 4.1.3.2.-3 examples of the operation characteristic with the
basic angle.
Fig. 4.1.3.2.-1 Operation characteristic of the directional earth-fault protection
unit when the basic angle
ϕ
b
= 0
°
, operation sector
∆ϕ
=
±
80° and
the wider operation sector
ϕ
a
=40°
Fig. 4.1.3.2.-2 Operation characteristics when the basic angle ϕ
b
= 0°, operation
sector ∆ϕ=±80° and the wider operation sector ϕ
a
=40°.
OPERATION
AREA
Io>
OPERATION
AREA
5
-80° -60° -40° -20°
0° 20° 40° 60° 80° 100°-100°
1
2
3
4
6
NON-OPERATION AREA
ϕb=0°
∆ϕ=80°
Io
In
-120°-140°
ϕa=40°
Ba_0_deg
Negative
quadrant
Positive
quadrant
OPERATION SECTOR
ϕ
b=0°
∆ϕ=80°
Uo
Io
ϕ
∆ϕ
Io>
LEAD
LAG
ϕa=40°
Ba_0_degrees
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Fig. 4.1.3.2.-3 Operation characteristics when the basic angle
ϕ
b
= -90
°
2) The operation of the directional earth-fault unit with sin(ϕ) or cos(ϕ)
characteristics is based on measuring the earth-fault current I
0
and the zero-sequence
voltage U
0
and further the phase angle ϕ between the voltage and current. The sinus
or cosinus value for the phase angle is calculated and then multiplied by the earth-
fault current. This will give the directional earth-fault current Iϕ
as a result. The
earth-fault stage starts if the following three criteria are fulfilled at the same time:
• The directional earth-fault current Iϕ exceeds the set starting level of the earth-
fault stage. The earth-fault unit has two earth-fault current stages I
0
> and I
0
>>.
• The zero-sequence voltage U
0
exceeds the set starting level. The unit has one
starting level, U
0b
>, serving both stages in deblocking mode.
• The phase angle ϕ between the voltage and current falls within the operation
sector of the angle correction factor ϕ
c
=2…7°.
When an earth-fault stage starts, a starting signal is generated and simultaneously the
display on the front panel indicates starting. If the above mentioned criteria are
fulfilled long enough to exceed the set operate time, the stage that started initiates a
tripping signal. At the same time the operation indicator on the front panel is lit. The
red operation indicator remains lit even if the protection stage resets. The direction
towards the fault spot is determined by means of the angle between the voltage and
current. The directional earth-fault characteristic sin(ϕ) corresponds to the earth-
fault protection with the basic angle -90° and cos(ϕ) to the earth-fault protection
with the basic angle 0°.
In Fig. 4.1.3.2.-4 and Fig. 4.1.3.2.-5 examples of the operation characteristics sin(ϕ)
and cos(ϕ).
Uo
Io
ϕ
∆ϕ
OPERATION SECTOR
ϕ
b=-90°
∆ϕ=80°
Io>
LEAD
LAG
Ba_-90_degrees
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Fig. 4.1.3.2.-4 Operation characteristic sin(
ϕ
)
Fig. 4.1.3.2.-5 Operation characteristic cos(ϕ)
The operation directions, forward or reverse, for the directional earth-fault stages
can be selected independently of each other. The directional stages may also be
configured separately as non-directional protection stages.
When the earth-fault current exceeds the set start current of the low-set stage I
0
>, the
earth-fault unit starts delivering a start signal after a preset ~ 70 ms start time. When
the set operate time at definite-time operation or the calculated operate time at
inverse-time operation elapses, the earth-fault unit operates. In the same way, the
high-set stage I
0
>> of the earth-fault unit starts delivering a start signal after a preset
ϕ
Io
Uo
Io>(>)
ϕc=2..7°
ϕc=2..7°
Sin_fi_char
ϕ
Io
Uo
Io>(>)
ϕc=2..7°ϕc=2..7°
Cos_fi_char
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~ 60 ms start time when the set start current is exceeded. When the set operate time
elapses, the earth-fault unit operates.
The low-set stage of the earth-fault unit may be given a definite-time or an inverse
definite minimum time (IDMT) characteristic. When the IDMT characteristic is
chosen, six time/current curve groups are available. Four of the groups comply with
the standards IEC 60255 and BS 142, and are called “normal inverse”, “very
inverse”, “extremely inverse” and “long time inverse”. The two additional inverse-
time curve groups are called “RI-” and “RD-curves”.
The inverse-time function of stage I
0
> can be inhibited when stage I
0
>> is started.
In this case, the operate time is determined by stage I
0
>>.
If not needed, the stage I
0
>> can be set out of operation completely. This state is
indicated by three dashes “---” on the LCD and by “999” when the set start current
value is read via serial communication.
The set start current value I
0
>>/I
n
of stage I
0
>> can be automatically doubled in a
start situation, i.e. when the object to be protected is connected to a network. Thus a
set start current value below the connection inrush current level may be selected for
the stage I
0
>>. A start situation is defined as a situation where the phase current rises
from a value below 12 % x I
0
> to a value above 150 % x I
0
> in less than 60 ms. The
start situation ends when the current falls below 125 % x I
0
>.
4.1.3.3. Zero-sequence voltage unit
The two current stages I
0
> and I
0
>> can be replaced by two additional voltage
stages, making the unit a three-stage zero-sequence voltage module. All the three
stages measure the same voltage but can have separate settings both for sensitivity
and operate time. The signalling and trip relays can also be selected separately for
all the three stages.
When the zero-sequence voltage exceeds the start voltage value set for the low-set
stage U
0
>, the voltage unit starts delivering a start signal after a preset ~ 70 ms start
time. When the set operate time at definite-time operation elapses, the voltage unit
operates. In the same way, the high-set stage U
0
>> of the voltage unit starts
delivering a start signal after a preset ~ 60 ms start time, when the set start voltage
is exceeded. When the set operate time elapses, the unit operates.
The low-set and high-set stages of the zero-sequence voltage unit operate on the
basis of the definite-time characteristic.
The high-set stage U
0
>> may be set out of operation by means of the switch SGF2/
3. When the stage is out of operation, three dashes “---” on the display and “999” in
communication via the serial bus indicate that the operation value is infinite.
ABB Substation Automation
Products and Systems
Technical Reference ManualREJ 527
18 1MRS750616-MUM
4.1.3.4. Protection against intermittent earth-faults
A typical example of an intermittent earth-fault would be one in an insulated cable
where the insulation has a crack and water leaks into the cable and causes an earth-
fault. The earth-fault dries up the crack in the cable, extinguishing the fault, but after
a short time water leaks back through the crack and the earth-fault reappears. The
process repeats giving a succession of fault current pulses.
Fig. 4.1.3.4.-1 Intermittent fault
When the reset time of the overcurrent relay is less than the interval between the
fault current pulses, the relay will be continually reset and not be able to integrate up
to the trip level. Having the reset time set to give as long a delay as possible, but less
than one that would interfere with normal operation of the protection and control
system, will help to eliminate some less common health and safety problems.
Fig. 4.1.3.4.-2 Settable resetting time
The reset delay is settable to values 80, 100, 500 and 1000 ms via the switchgroup
SGF5. If the resetting time is set to 100 ms or above, the earth-fault stage I
0
>
operates as an intermittent earth-fault stage.
Momentary peak
value of neutral
current Io
Momentary
value of
neutral
voltage Uo
Fundamental
amplitude of Io
In
t
e
r
m
2
Set value
Trip level
≥100ms
≥100ms
Resettime
1MRS750616-MUM 19
REJ 527Technical Reference Manual
ABB Substation Automation
Products and Systems
4.1.3.5. Time/current characteristics
The low-set earth-fault current stage I
0
> can be given a definite-time or an inverse
definite minimum time operation characteristic. The settings of switches SGF4/1...6
determine the operation mode of stage I
0
>. Refer to section “Settings” beginning
from page 23. At the IDMT characteristic, the operate time of the stage is a function
of the current: the higher the current, the shorter the operate time. Six time/current
curve groups are available. Four of these comply with the standards IEC 60255 and
BS 142 and two curve groups, RI and RD, are special type curve groups according
to ABB praxis.
Characteristics according to IEC 60255 and BS 142
The relationship between time and current is in accordance with the standards IEC
60255-3 and BS 142, and can be expressed as follows:
where t = operate time
k = time multiplier
I
0
= phase current value
I
0
> = set current value.
The standard BS 142.1966 defines the normal current range to be 2...20 times the
setting value. In addition, the relay has to start at the latest when the current exceeds
the setting value 1.3 times if the time/current characteristic is normal inverse, very
inverse or extremely inverse. For the long-time inverse characteristic the normal
current range is specified to be 2...7 times the setting, and the relay is to start when
the current exceeds the setting value 1.1 times.
Table 1: The values of constants α and β.
Time/current curve group
αβ
Normal inverse 0.02 0.14
Very inverse 1.0 13.5
Extremely inverse 2.0 80.0
Long-time inverse 1.0 120
ts[]
k β×
Io
Io>
---------
α
1–
---------------------------=
ABB Substation Automation
Products and Systems
Technical Reference ManualREJ 527
20 1MRS750616-MUM
E = accuracy in per cent; - = not specified
In the normal current range, specified above, the inverse-time stages of the
directional or non-directional earth-fault relay fulfil the tolerance requirements of
class 5 at all degrees of inversity.
The time/current characteristics according to the IEC and BS standards are
illustrated in Fig. 4.1.3.5.-1...Fig. 4.1.3.5.-2.
RI-type characteristic
The RI-type characteristic is a special characteristic that is principally used for
obtaining time grading with mechanical relays. The characteristic can be expressed
mathematically:
where t = operate time in seconds
k = time multiplier
I
0
= phase current
I
0
> = set start current.
The RI-type characteristic is illustrated in Fig. 4.1.3.5.-3.
Table 2: The operate time tolerances specified by the standard
I
0
/I
0
> Normal Very Extremely Long time
2 2,22E 2,34E 2,44E 2,34E
5 1,13E 1,26E 1,48E 1,26E
7---1,00E
10 1,01E 1,01E 1,02E -
20 1,00E 1,00E 1,00E -
ts[]
k
0.339 0.236–
Io>
Io
---------
×
-------------------------------------------------=
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