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15.10 NUMERICAL BUSBAR PROTECTION
SCHEMES
The application of numerical relay technology to busbar
protection has lagged behind that of other protection
functions. Static technology is still usual for such
schemes, but numerical technology is now readily
available. The very latest developments in the
technology are included, such as extensive use of a data
bus to link the various units involved, and fault tolerance
against loss of a particular link by providing multiple
communications paths. The development process hasbeen very rigorous, because the requirements for busbar
protection in respect of immunity to maloperation are
very high.
The philosophy adopted is one of distributed processing of
the measured values, as shown in Figure 15.20. Feeders
each have their own processing unit, which collects
together information on the state of the feeder (currents,
voltages, CB and isolator status, etc.) and communicates
it over high-speed fibre-optic data links to a central unit.
For large substations, more than one central unit may be
used, while in the case of small installations, all of theunits can be co-located, leading to the appearance of a
traditional centralised architecture.
For simple feeders, interface units at a bay may be used
with the data transmitted to a single centrally
located peripheral unit. The central unit performs the
calculations required for the protection functions.
Available protection functions are:
a. protection
b. backup overcurrent protection
c. breaker failure
d. dead zone protection
In addition, monitoring functions such as CB and isolator
monitoring, disturbance recording and transformersupervision are provided.
Because of the distributed topology used,
synchronisation of the measurements taken by theperipheral units is of vital importance. A high stability
numerically-controlled oscillator is fitted in each of the
central and peripheral units, with time synchronisation
between them. In the event of loss of thesynchronisation signal, the high stability of the oscillatorin the affected feeder unit(s) enables processing of the
incoming data to continue without significant errors
until synchronisation can be restored.
The peripheral units have responsibility for collecting the
required data, such as voltages and currents, and
processing it into digital form for onwards transmissionto the central unit. Modelling of the CT response is
included, to eliminate errors caused by effects such as CTsaturation. Disturbance recording for the monitored
feeder is implemented, for later download as required.
Because each peripheral unit is concerned only with anindividual feeder, the protection algorithms must reside
in the central unit.
The differential protection algorithm can be much more
sophisticated than with earlier technology, due to
improvements in processing power. In addition tocalculating the sum of the measured currents, the
algorithm can also evaluate differences betweensuccessive current samples, since a large change above a
threshold may indicate a fault the threshold being
chosen such that normal load changes, apart from inrushconditions do not exceed the threshold. The same
15
BusbarProt
ection
N e t w o r k P r o t e c t i o n & A u t o m a t i o n G u i d e 2 5 1
Figure 15.20: Architecture for numerical protection scheme
Personal
Computer
PU
CT
CBPU CB
CT
PU CB
CT
Feeder 1 Feeder 2
CU
Central Unit
PU
Fibre optic link
System Communication Network
PU: Peripheral Unit
CU: Central Unit
CB
CT
Chap15-232-253 17/06/02 9:54 Page 251
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considerations can also be applied to the phase angles ofcurrents, and incremental changes in them.
One advantage gained from the use of numericaltechnology is the ability to easily re-configure theprotection to cater for changes in configuration of thesubstation. For example, addition of an extra feeder
involves the addition of an extra peripheral unit, thefibre-optic connection to the central unit and entry viathe MMI of the new configuration into the central unit.Figure 15.21 illustrates the latest numerical technologyemployed.
15.10.1 Reliability Considerations
In considering the introduction of numerical busbarprotection schemes, users have been concerned withreliability issues such as security and availability.Conventional high impedance schemes have been one of
the main protection schemes used for busbar protection.The basic measuring element is simple in concept andhas few components. Calculation of stability limits andother setting parameters is straightforward and schemeperformance can be predicted without the need forcostly testing. Practically, high impedance schemes haveproved to be a very reliable form of protection.
In contrast, modern numerical schemes are morecomplex with a much greater range of facilities and amuch high component count. Based on low impedancebias techniques, and with a greater range of facilities toset, setting calculations can also be more complex.
However, studies of the comparative reliability of
conventional high impedance schemes and modernnumerical schemes have shown that assessing relativereliability is not quite so simple as it might appear. Thenumerical scheme has two advantages over its oldercounterpart:
a. there is a reduction in the number of externalcomponents such as switching and other auxiliaryrelays, many of the functions of which areperformed internally within the softwarealgorithms
b. numerical schemes include sophisticatedmonitoring features which provide alarm facilities
if the scheme is faulty. In certain cases, simulationof the scheme functions can be performed on linefrom the CT inputs through to the tripping outputsand thus scheme functions can be checked on aregular basis to ensure a full operational mode isavailable at all times
Reliability analyses using fault tree analysis methodshave examined issues of dependability (e.g. the ability tooperate when required) and security (e.g. the ability notto provide spurious/indiscriminate operation). Theseanalyses have shown that:
a. dependability of numerical schemes is better thanconventional high impedance schemes
b. security of numerical and conventional highimpedance schemes are comparable
In addition, an important feature of numerical schemesis the in-built monitoring system. This considerablyimproves the potential availability of numerical schemescompared to conventional schemes as faults within theequipment and its operational state can be detected andalarmed. With the conventional scheme, failure to re-instate the scheme correctly after maintenance may notbe detected until the scheme is required to operate. Inthis situation, its effective availability is zero until it isdetected and repaired.
15.11 REFERENCES
15.1 The Behaviour of Current Transformers subjectedto Transient Asymmetric Currents and theEffects on Associated Protective Relays. J.W.Hodgkiss. CIGRE Paper Number 329, Session15-25 June 1960.
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N e t w o r k P r o t e c t i o n & A u t o m a t i o n G u i d e 2 5 2
Figure 15.21: Busbar protection relay using thelatest numerical technology (MiCOM P740 range)
BusbarProt
ection
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The MiCOM P740 numerical busbar protection
scheme provides complete protection for all
types of extra / ultra high voltage busbar
configurations.
Built on a number of innovative techniques,
including CT saturation detection and dynamic
topology processing algorithms, the P740 offers
a unique combination of security, speed and
sensitivity.
With a typical operating time of 15ms, the P740
protection is one of the fastest in its class and
meets the most stringent requirements of extra /
ultra high voltage transmission systems.
The substation replica processing algorithms
ensure that P740 adapts to the dynamically
changing topology of the busbar.
The MiCOM P740 busbar differential protectionscheme can be engineered to provide a
centralized or a distributed architecture. It also
supports easy maintenance, operation and future
expansion of the busbar.
Customer benefits
Fast fault trip(typically 15ms)
Adaptable to any busbarconfiguration.
Can operate with differenttypes of CT.
Fibre optic cable used forcommunication betweenCentral and Peripheral Units:- Ensures high
communication speed- Eliminates insulation
problems
AREVA T&D
MiCOM P740Numerical Busbar Protection
PROTECTION
MiCOM P741 in 80TE
MiCOM P743 in 60TE
MiCOM P742 in 40TE
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APPLICATION
The MiCOM P740 numerical busbar protection scheme
has been designed to protect a wide range of busbar
configurations. The modular scheme comprises of three
relays:
Central Unit - P741
Peripheral Unit - P742 / P743
These units, interconnected using optic fibre cables
together with the topology configurator software allow
application to all types of busbar configurations.
The Central Unit co-ordinates the scheme, receiving
signals from all the peripheral units associated with the
protected busbars and acting on these signals, initiating
a buszone protection trip when necessary. A single
Central Unit can accommodate upto,
8 Zones
28 Peripheral Units
One Peripheral Unit is associated with each
CT location, usually one per incomer/feeder and one
or two for each bus coupler/bus section, depending on
number of CT (1 or 2). The Peripheral Units acquire
the analogue signals from the associated CT and the
binary signals from the auxiliary contacts of circuit
breakers and isolators.The Peripheral Units also
incorporate the main circuit breaker failure logic
together with backup protection.
The difference between the P742 and P743 is in the
number of I/O that each can accommodate. The P743
allows for increased I/O, this is particularly useful in
double busbar applications. Especially where single
pole breakers and transfer busbar are employed, in
these applications the I/O requirements are large in
comparison to those required for a single busbar
application where a P742 may be more suitable.
2>3
Complete flexibility to suitany busbar configuration
P740 scheme
applied for protecting
double busbar with transfer bus
BB1
Central UnitOptical fibre Peripheral UnitsPeripheral Units
BB2
BB3
BB4
TransferBus
2 P742 or2 P743
P742 P743 P741 P742P743
PROTECTION
FUNCTIONS
OVERVIEW P74 P74 P743
87BB / P Phase segregated biased current - -differential high speed busbar protection
87BB / N Sensitive earth fault bias current controlled - -busbar protection
87 CZ Check zone element (supervision) - -50 / 51 / P Phase overcurrent protection (2 stages) - 50 / 51 / N Earth overcurrent protection (2 stages) - 50ST Dead zone protection (short zone between CTs and CBs) - -CTS Current transformer supervision 50BF Breaker failure protection (LBB) ISL Isolator discrepancy alarm -
Fibre optic signalling channel Digital inputs 8 16 24
Output relays 8 8 21
Front communication port (RS232) Rear communication port (RS485) Time synchronisation port (IRIG-B) * option - -
* Refer data sheet for model selection
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MANAGEMENT FUNCTIONS
In addition to the protection and control elements, the
P740 scheme provides a wide range of measurement,
monitoring, post fault analysis and self-diagnostic
features:
Circuit breaker control
Trip circuit supervision (using PSL)
On-line measurement
Plant status monitoring 4 alternative setting groups
Programmable scheme logic (PSL)
Sequence of event recording (SOE)
Comprehensive disturbance recording (waveform
capture)
User configurable LEDs
Local and remote communication ports
Time synchronisation
Fully customisable menu texts
Multi level password protection
Test facilities
Power-up diagnostics and continuous self-monitoring
of relay.
User friendly setting and analysis software
Speed, Sensitive & Secure:P740 the ultimate in busbar protection
X
/
/
/ /
Fault records
Measurements
PSL
Local
Communication
Remote
comm. port
Busbar protection scheme
Peripheral Unit P742 / P743
LEDsBinaryInput / output
Self monitoring
50/
51/P
50/
51/N
50ST
Disturbance
Record
Fibre optic
signaling
channel
50BF CTS
Fault records
Measurements
PSL
Local
Communication
Remote
comm. port
Busbar protection schemeCentral Unit P741
LEDsBinaryInput / output
Self monitoring
87BB
/ P
87BB
/ N 87CZ
Disturbance
Record
Fibre optic
signaling
channel
50BF CTS
ISL
FUNCTIONAL OVERVIEW
(Description of ANSI code nos. see Protection Function Overview)
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The P740 employs biased differential algorithms, in
which the differential current is compared with a bias
current. This characteristic ensures stability of the
protection for external fault even with differing CT
tolerances and errors which otherwise could lead to
spurious operation.
To increase the security of the differential protection,
the biased differential element is supervised by a
global check zone element. This ensures stability
even under erroneous status of the auxiliary contact of
plant isolators and circuit breakers.
The MiCOM P740 also employs an innovative, ultra
high-speed, secure CT saturation detection
algorithm. This ensures stability when CTs become
saturated, particularly under external fault conditions.
This algorithm combine a simulation of the flux built up
in the core of the CTs with a recursive consistence
variation control.This technique can detect CT
saturation in less than 2ms.
4>5
i (t)bias
I > 2Di3 in
i2i1
I > 1D
Ispe
rcenta
gebias
-k=20t
o90%
Tripping
Area
Restrain
area
i (t)diff nodeDifferential current : = + + i n1 2 iii 3 + ....... +
i (t)diffOperating current : = = i
i (t)diff
i (t)bias i 1 i 2 i 3 i nRestraining current : =+ + + ....... + = i
i (t)diff node
Universal on-line topology processing
Bias differential characteristics
CT saturation detection
To ensure adaptability of the relay to any type of
busbar configuration the P740 is built with a universal
topology processing algorithm. This algorithm
determines the optimum tripping zone on-line based
on the status of the plant isolator and breakers.
This ensures that minimum part of the busbar is
isolated for any fault in it.
BUSBAR DIFFERENTIAL PROTECTION
The primary protection element of the P740 scheme is
the phase segregated biased current differential
protection. The technique is based on the numerical
application of Kirchoff's Law for the selective detection
and ultra high-speed isolation of a faulty section of the
busbar.
The analysis is carried out in the Central Unit (CU)
which communicates with the Peripheral Unit (PU) to
get the current flowing in individual circuits and to
implement the tripping of circuits as decided by it.
This reliable, high speed communication is achieved
via a direct optical connection utilising a 2.5 Mbps
data rate.
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DUAL CHARACTERISTICS
To provide stability for severe through faults and at the
same time detect low current internal faults, the P740
is equipped with dual characteristics. One phase
segregated differential protection and another
sensitive earth current differential protection.
MULTIPLE TRIPPING CRITERIA
The MiCOM P740 maintains the highest level of
stability, under all conditions including a hardware
failure and incoherent signals applied from external
plant equipment or generated by power system.
Any tripping order must therefore be made conditional
on the simultaneous occurrence of 5 or 6 criteria:
> Magnitude criteria; confirmation of two simultaneous
thresholds per zone:
Exceeding the bias slope characteristic (k)
Exceeding differential operating current threshold
(ID>2).
> Exceeding the supervision threshold (ID>1).
> Signal quality criteria:
No CT saturation detected
Current variation detected on at least two
Peripheral Units
> Time or angular criterion.
The measurement elements on 2 samples taken at
1200 Hz. A first sample for the initial measurement
and a second sample for tr ip confirmation.
> Check zone supervision.
The zone element(s) are only permitted to trip if the
order is confirmed by the check zone element.
> Local criteria (optional)
The Peripheral Units can be set to only authorise
tripping if there is confirmation by local overcurrent
criteria.
DEAD ZONE OR BLIND SPOTPROTECTION
The current transformers surrounding the busbars
define the limits of the main zones. When the circuit
breaker is opened a dead zone or blind spot is created
between the CB and the associated CT. The P740
detects this condition automatically and provides
protection for this zone also.
CONTINUOUS SUPERVISION
OF CURRENT CIRCUITS
The P740 detects any abnormality in the current circuit
by continuously monitoring it. Under normal operating
conditions the differential current will be negligible. An
anomaly is detected by a threshold, ID>1, which can
be set to alarm from 1% of the primary basis current
(Ibp).
DIFFERENTIAL CURRENT SETTING
When switching operations are carried out in the
substation, incorrect topology replicas may occur. In
this case, a differential current appears. The
differential elements of the MiCOM P740 are allowed
to operate only if the differential current reaches a
threshold ID>2which is set above the highest load
current.
ADDITIONAL ULTRA HIGH SPEEDEXTERNAL FAULT BLOCKING
The ultra high-speed saturation detection is carried out
in each PU and can generate a control signal from the
moment of the first sample (0.4 ms).
Dual characteristics
PU1connectedto BB1
PU2 not connected to BB1= Activation
of Dead Zone protection
CB OpenCB Closed
Dead Zone
BB1
Intertrip contact
to other end
ID>2
Trip
ISID>1
idiff
Perce
ntage
bias-
k
IDN>2Restrain
Trip
IIDN>1
ibias
ibias
idiff
Percentage
bias- kN
SEF Block threshold
kNmin =0.2
BlockEnable
Restrain
SN
Dead zone protection
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6>7
Programmable scheme
logic editor (MiCOM S1)
PHASE OVERCURRENT ANDEARTH FAULT PROTECTION
Two independent stages each of phase overcurrent and
earth fault protection is provided in the Peripheral Units.
These elements provide backup protection for the
individual circuits.
The two stages can be programmed as:
> First stage can be programmed as definite time (DT)
delay or one of the nine inverse time (IDMT) curves
(IEC/UK and IEEE/US).
> Second stage can only be programmed as definite
time.
CIRCUIT BREAKER FAILUREPROTECTION (LBB)
The MiCOM P740 busbar protection scheme can work
in co-ordination with external breaker failure
protection relays. In this configuration, the receipt of an
external breaker failure information results in tripping of
all the adjacent circuit breakers, via the topological
recognition system knowing which breaker is connected
to which zone.
The P740 also offers an in-built integrated solution
for breaker failure protection. This requires all
Peripheral Units to receive a duplication of the trip
commands generated in their associated bay.
In general the Breaker Failure protection must be
executed on a per phase basis which involves the
possibility of receiving tripping orders on a per pole
basis.
CURRENT TRANSFORMERMISMATCH CORRECTION
The MiCOM P740 can correct mismatch between
current transformer ratios over a very wide range up
to 40. Its associated user interface provides a range
between 1 A and 30,000 A primary.
Since the current transformer ratings in a substation
may be of mixed ratios, the MiCOM P740 enables a
common base current to be defined, irrespective of
the feeder section concerned.
The settings on the Central Unit are all adjusted to this
common current, known as the primary base current (Ibp).
ISOLATION AND MAINTENANCEOPERATING MODE
For ease of operation or maintenance of the busbar
protection system, the Central Unit and the Peripheral
Units can receive specific commands designed to
allow system testing or other intervention without any
danger of unwanted tripping.
In the Central Unit, a centralized command to isolate
the busbars at two levels can be applied selectively
zone wise:
> Differential protection (87 BB) in monitoring mode
(measurements active and tripping deactivated).The
Breaker Failure protection remains operational.
> Differential protection (87 BB) and Circuit Breaker
Failure protection (50 BF) in monitoring mode.The
additional local protection functions (51, 51N, etc...)
remain operational.
A selective two-level command may be applied
selectively for each Peripheral Units:
> Maintenance of bay(s) for human intervention.
In this state, all I/O are deactivated.The busbarprotection is still in service, but the CB of the feeder
in service can not be tripped.
> Intervention on the equipment for maintenance and
testing.
PROGRAMMABLE SCHEME LOGIC
Powerful programmable scheme logic (PSL) allows the
user to customize the protection and control functions.
It is also used to programme the functionality of the
optically isolated inputs, relay outputs and LED
indications.The programmable scheme logic
comprises of gate logic and general purpose timers.
The gate logic includes OR, AND and majority gate
functions, with the ability to invert the inputs and
outputs, and provide feedback.The programmable
scheme logic is configured using the graphical MiCOM
S1 PC based support software.
PLANT STATUS
Checks and monitoring of the plant status can be
made, and an alarm raised for any discrepancy
conditions between the open and closed auxiliary
contacts of the isolators and circuit breakers.
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MEASUREMENTAND RECORDING FACILITIES
The P740 series relays are capable of measuring and
storing the values associated with a fault. All the
events, faults records and disturbance records are time
tagged to 1 ms using an internal real time clock. An
optional IRIG-B port is also provided for accurate time
synchronization. A lithium battery provides a back up
for the real time clock and all records in the event of
supply failure.
MEASUREMENTS
The measurements provided, which may be viewed in
primary or secondary values, can be accessed via
the back lit liquid crystal display. They are also
accessible via the communication ports. The following
instantaneous parameters can be viewed:
> Central unit (P741
Differential current Idiff / phase / zone
Bias current Ibias / phase / zone
Check zone Idiff / phase> Peripheral units (P742 & P743)
Phase currents IA IB IC
Neutral current IN
Sequence currents
Frequency
EVENT RECORDER
Up to 250 time tagged event records are stored in
battery backed memory, and can be extracted via the
communication port or be viewed on the front panel
display.
FAULT RECORDER
Records of the last 5 faults are stored in the
battery-backed memory of both the Central and
Peripheral Units.
Each fault record includes:
> Indication of the faulty zone (CU + PU)
> Protection element operated
> Active setting group
> Fault duration
> Currents and frequency (PU)
> Faulty zone differential and bias current (CU)
DISTURBANCE RECORDER
The Central and Peripheral units of the P740 have
independent disturbance recording facility. The
Peripheral Units can record 4 analogue and 32 digital
channels, whereas the Central unit stores 8 analogue
and 32 digital channels in addition to 1 time channel.
> Specific analogue channels Ibias / Idiff (CU)
IA, IB, IC, IN (PU)
> Maximum duration of one record and number of
records
1.2s per record and 8 records (CU)
up to 10.5s per record and minimum of
20 records (PU)
Disturbance records can be extracted from the relay
via the remote communications and saved in the
COMTRADE format. These records may be examined
using MiCOM S1 or any other standard COMTRADE
viewer.
Disturbance record viewed in MiCOM S1
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LOCAL AND REMOTECOMMUNICATIONS
Two communication ports are available as standard; a rear
port providing remote communications and a front port
providing local communications.
The front RS232 port has been designed for use with MiCOM
S1, which fully supports functions within the relay by providing
the ability to programme the settings off-line, configure the
programmable scheme logic, extract and view event,
disturbance and fault records, view the measurement
information dynamically and perform control functions (using
Courier protocol).
The default remote communications is Courier / K-bus and can
be converted to IEC60870-5-103.
DIAGNOSTICS
Automatic tests performed including power-on diagnostics andcontinuous self-monitoring ensures a high degree of reliability.
The results of the self-test functions are stored in battery
backed memory. Test features available on the user interface
provide examination of input quantities, states of the digital
inputs and relay outputs. A local monitor port provides digital
outputs, selected from a prescribed list of signals, including the
status of protection elements.
HARDWARE
All models within the MiCOM P740 series relays include:
> A back-lit liquid crystal display
> 12 LEDs
> Optional IRIG-B port (CU),
> RS232 (front port) & RS485 (rear port),
> Fibre optic connection from the CU to the PUs,
> Download/monitor port,> Battery (supervised),
> N/O and C/O watchdog contacts
> Supervised +48 V field voltage
> Dual rated CT inputs 1A/5A
> Universal opto inputs with progammable voltage threshold
The optically isolated inputs are independent and may be
powered from the +48V field voltage.
Our policy is one of continuous development. Accordinglythe design of our products may change at any time. Whilstevery effort is made to produce up to date literature, thisbrochure should only be regarded as a guide and isintended for information purposes only. Its contents do notconstitute an offer for sale or advise on the application ofany product referred to in it. We cannot be held responsiblefor any reliance on any decisions taken on its contentswithout specific advice.
AUTOMATION-L3-P740-BR-05.05-1021-GB
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Tel.: +44 (0) 1785 250 070
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Device Track Record
>> Low impedance biased differential busbar protection, MBCZ,
launched in 1988 and over 800 cubicles sold
>> Over 200 DIFB, medium impedance biased differential busbar
protection scheme delivered since its launch in 1992.
>> Medium impedance biased differential busbar protection with linear current
combination, DIFB CL, launched in 1996. Over 70 cubicles delivered.
>> Since the launch of the P740, over 50 systems have been delivered.
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Customer benefits This architecture can
accommodate the mostcomplex substation layouts
and different CT classesand manufacturers.
The use of fibre optics forcommunication betweenPeripheral Units and theCentral Unit gives thefollowing advantages:
- High communicationspeed
- Eliminates insulationproblems
Fast fault clearance(Typical tripping time 15 ms).
>
T&DEnergy Automation & Information
MiCOM P740
Numerical Busbar Protection
>> The consequences of a faulton the busbars of a powertransmission or distributionnetwork substation may be veryserious. Poor quality of supply toconsumers and damage to theelectrical equipment are veryreal threats.
ALSTOM has developed a newand fully numerical busbarprotection. The primary
objectives are to provide totalprotection stability under normaloperating conditions and for allexternal faults, whilst reactingquickly to internal faults. Thisprotection scheme is theMiCOM P740.
The MiCOM P740 provideshigh-speed protection ( Distributed architecture (up to 1.000 m
of optical fibre) or in a centralised cubicle.
> Topological configuration can
accommodate up to 8 zones.
> Advanced topological analysis using
operational research algorithms
(registered patent).
> Trip supervision by "check zone"
element for security.
> Low CT requirements allow the core
to be shared with existing protection.> Innovative algorithms for CT
saturation detection
(registered patent).
The minimum permitted saturation
time is 2 ms for stability.
> Bias characteristics to maintain
stability during transient CT responses
in presence of a significant DC
component.
> Security against accidental open
circuit of CTs by the use of delta
algorithms.
> Phase segregation with a separateelement for sensitive earth fault
detection (high impedance earthed
networks).
> Automatic control of the sensitive
earth fault element by phase elements.
> User-friendly interface for operation
and commissioning staff including
two levels of maintenance.
Our products>
> >
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Main protection functions
> Architecture
The architecture of the numerical
differential busbar protection is builtaround a P741 Central Unit (CU) whichgathers and processes all the analoguemeasurements from the P742 and P743Peripheral Units (PU) via direct fibreoptic connections.It is possible to protect:
8 zones.
32 Peripheral Units per Central Unit.
> Protection
> Central Unit (P741)
Busbar bias differential protection. Check Zone protection
Breaker Fail protection
(general 3 poles trip).
> Peripheral Units (P742/3)
Dead zone protection (short zone
between CTs and circuit-breakers).
Non directional Overcurrent
protection.
- Phase fault (2 stages).
- Earth fault (2 stages).
Breaker Fail protection
(single or three pole retrip).
Busbar protection
The operation of the MiCOM P740 isbased on the numerical application ofKirchoff's Law for the selective detectionand ultra high-speed isolation of afaulty section of a busbar.
> Universal topologicalprocessing algorithms
The MiCOM P740 uses new universalalgorithms based on operational
research which create, in real time,architectures of up to 8 zones.
> Stabilisation againstCT saturation
One of the most important objectives ofa differential busbar protection is toensure stability when CTs becomesaturated, particularly under externalfault conditions.In order to avoid this risk ofmaloperation, the MiCOM P740 usesinnovative ultra high-speed algorithmsbased on signal consistence variationmodel (registered patent).
> Bias characteristic
The operation of the MiCOM P740 isbased on an algorithm with acharacteristic (see figure 2) in which the
differential current is compared with abias value.The purpose of this characteristic is toensure the stability of the protection
when there is an external fault, differingCT tolerances and errors whichotherwise would lead to spuriousdetection of an in-zone fault.
> Global supervision by
check zone element
One of the most frequent causes of themaloperation of busbar protectionschemes is an error in actual plantstatus. This leads to the production of adifferential current.
2
Models available
Features P741 P742 P743
CentralUnit
PeripheralUnit
Peripheral
Unit87BB/P
87BB/N
87CZ
50/51/P
50/51/N
CTS
50BF
8 Opto Universal Inputs, 8 Output relays(MiCOM 16case, 80 TE)
16 Opto Universal Inputs, 8 Output relays(MiCOM 8case, 40 TE)
24 Opto Universal Inputs, 21 Output relays
(MiCOM 12case, 60 TE)
Phase segregated currentdifferential busbar protection
Sensitive earth fault busbar protectionCheck zone element (Supervision)
Phase Overcurrent protection
Earth Overcurrent protection
Current transformers supervision
Breaker fail protectionLocal single orthree pole re-tripGeneral three poleback-trip
Fibre Optic signalling channels
Figure 1
Double Busbarwith transfer bus
BB1
CentralUnitOptical Fibre Peripheral UnitsPeripheral Units
BB2
BB3
BB4
TransferBus
2 P742or
P743
P742 P743 P741 P742P743
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However, if all currents of the wholesubstation are taken into account, theirsum will remain null if a fault is notpresent, irrespective of the error in plantstatus/position.Consequently, the tripping order for azone element is conditional on theoperation of a check zone element.The main advantage of this element isthe total insensitivity to defectiveauxiliary contacts.
> Dead zone or Blind spot
The current transformers surrounding thebusbars define the limits of the mainzones. When the circuit breaker isopened a dead zone or blind spot isautomatically created between the CBand the associated CT.
> Continuous supervision of thecurrent circuits by
measurement of thedifferential current value
Under normal operating conditions thedifferential current will be negligible. Ananomaly is detected by a threshold,ID>1, which can be set to alarm from1% of the primary basis current (Ibp).
> Differential current setting
When switching operations are carriedout in the substation, incorrect topologyreplicas may occur. In this case, adifferential current appears.The differential elements of the MiCOMP740 are allowed to operate only if thedifferential current reaches a thresholdID>2 which is set above the highest loadcurrent.
> Stabilisation of the protectionin the event of CT saturationfor external fault
One main quality of the MiCOM P740is its ability to detect CT saturation in
less than 2 ms.The signal processing algorithmsimplemented in the MiCOM P740combine a simulation of the flux built upin the core of the CTs with a recursiveconsistence variation control(registered patent).
> Additional ultra high speedexternal fault blocking
The ultra high-speed saturation detectionis carried out in each PU and cangenerate a control signal from themoment of the first sample (0.4 ms).
> Dual characteristics
The MiCOM P740 offers phase-segregated protection and a separateelement for earth fault detection.
> Multiple tripping criteria
The MiCOM P740 maintains the highestlevel of stability, under all conditionsincluding:
> A hardware failure
> Incoherence of signals applied from
external plant or generated by the
power system.
> Any tripping order must therefore be
made conditional on the simultaneous
occurrence of 5 or 6 criteria:
> Magnitude criteria; confirmation of
two simultaneous thresholds per zone:
Exceeding the bias slopecharacteristic (k)
Exceeding differential operating
current threshold (ID>2).
> Exceeding the supervision threshold
(ID>1).
> Signal quality criteria:
No CT saturation detected
Current variation detected on at
least two Peripheral Units
No discrepancy detected.
> Time or angular criterion.
The measurement elements on 2samples taken at 1200 Hz.
A first sample for the initial
measurement and a second sample
for trip confirmation.> Check zone supervision.
The zone element(s) are only
permitted to trip if the order is
confirmed by the check zone element.> Local criteria (optional)
The Peripheral Units can be set to
only authorise tripping if there isconfirmation by local overcurrent
criteria.
Additional protection
The following back-up protectionfunctions are implemented locally in thePeripheral Units (P742/P743).
> Phase and Earth Faultovercurrent protection either
Definite Time (DT) or IDMT(IEC/UK, IEEE/US curves)
Two independent stages are availablefor phase and earth:
> First stage (I>1 or IN>1) can be
programmed as Definite Time (DT)
delay or dependant on one of nine
inverse time (IDMT) curves
(IEC/UK and IEEE/US).
> Second stage (I>2 or IN>2) can only
be programmed as definite time.
> External Breaker Failureprotection from the busbarprotection system
The usual 50 BF relay is totallyindependent of the others and thecontrol connection with the busbarprotection system is hardwired. Receiptof an external 50BF information resultsin tripping of all the adjacent circuitbreakers, via the topological recognitionsystem knowing which breaker isconnected to which zone.
> Internal breaker failureprotection in the busbarprotection system
Some operators prefer an integratedsolution, which requires all PeripheralUnits to receive a duplication of the tripcommands generated in their associatedbay.In general the Breaker Failure protectionmust be executed on a per phase basis
which involves the possibility ofreceiving tripping orders on a per pole
basis.
i (t)bias
I > 2Di3 in
i2i1
I > 1DIs
perce
ntage
bias
-k=2
0to9
0%
TrippingArea
Restrainarea
i (t)diff nodeDifferential current : = + + i n1 2 iii 3+ ....... +i (t)diffOperating current : = = i
i (t)diff
i (t)bias i 1 i 2 i 3 i nRestraining current : = + + + ....... + = i
i (t)diff node
3
Figure 2
Biascharacteristic
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4
Matching CT Transformer ratios
> Balancing protection
The MiCOM P740 can correct mismatch
between current transformer ratios overa very wide range up to 40. Itsassociated user interface provides arange between 1 A and 30,000 Aprimary.
> Common base ratio
Since the current transformer ratings ina substation may be of mixed ratios, theMiCOM P740 enables a common basecurrent to be defined, irrespective of thefeeder section concerned. The settingson the CU are all adjusted to this
common current, known as the primarybasis current (Ibp).
Isolation and downgradedoperating mode
For ease of operation or maintenance ofthe busbar protection system, theCentral Unit and the Peripheral Unitscan receive specific commands designedto allow system testing or otherintervention without any danger of
unwanted tripping.
> Central Unit - CU (P741)
A central command to isolate thebusbars at two levels can be appliedselectively zone by zone.
> Differential protection (87 BB) in
monitoring mode (measurements
active and tripping deactivated).
The Breaker Failure protection
remains operational.
> Differential protection (87 BB) and
Circuit Breaker Failure protection
(50 BF) in monitoring mode. The
additional local protection functions
(51, 51N, etc...) remain operational.
> Peripheral Units - PU(P742 and P743)
A selective two-level command may beapplied selectively for each PU.
> Maintenance of bay(s) for human
intervention. In this state,
all I/O are deactivated.
The busbar protection is still in
service, but the CB of the feeder in
service can not be tripped.
> Intervention on the equipment for
maintenance and testing.
Control
> Circuit breaker control
The circuit breaker control is availablefrom the front panel user interface, orthe optically isolated inputs.
> Programmable scheme logic
Powerful Programmable Scheme Logic(PSL) allows the user to customise theprotection and control functions. It isalso used to program the functionality ofthe optically isolated inputs, relayoutputs and LED indications.The PSL uses up to 256 logic gates and8 timers and is configured using thegraphical MiCOM S1 PC basedsoftware as illustrated in Figure 3.
> Independent protection
settings groups
The settings are divided into twocategories: protection settings and
control and configuration settings. Foursettings groups are provided for theprotection settings to allow differentoperating conditions and adaptiverelaying.
Measurement and recording
facilities
The P740 series relays are capable ofmeasuring and storing the valuesassociated with a fault. All the events,faults records and disturbance records
are time tagged to 1 ms using aninternal real time clock. An IRIG-B portis also provided for accurate timesynchronisation.
A lithium battery provides a back up forthe real time clock and all records in theevent of supply failure.
> Measurements
The measurements provided, which maybe viewed in primary or secondary
values, can be accessed via the back litliquid crystal display. They are also
accessible via the communication ports.
> Instantaneous measurements
> Central unit (P741) Differential current
Idiff/phase/zone Bias Current
Ibias/phase/zone Check zone
Idiff/phase
> Peripheral units (P742 & P743) Phase currents IA IB IC
Neutral currentIN
Frequency f
Figure 3
Programmable Scheme Logic
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Post fault analysis
> Event recorder
Up to 250 time tagged event recordsare stored in battery backed memory,and can be extracted via thecommunication port or be viewed on thefront panel display.
> Fault recorder
Records of the last 5 faults are stored inthe battery-backed memory.
Each fault record includes: Indication of the faulted phase Indication of the faulted zone (CU) Protection element operated Active setting group Fault duration Currents and frequency (PU) Faulty zone differential and
bias current (CU)
> Disturbance Recorder
The internal disturbance recorder storeson non-volatile memory: 8 analogue channels
ibias/idiff (CU) iA, iB, iC, iN (PU)
32 digital channels 1 time channel Data is sampled 12 times a cycle 20 (PU) & 8 (CU) disturbance records Max. duration of each record for
PU: 10.5 s & CU: 600 ms All channels and trigger sources user
configured (PU)
Disturbance records can be extractedfrom the relay via the remotecommunications and saved in theCOMTRADE format.
These records may be examined usingMiCOM S1 or COMTRADE viewer.
Plant status
Checks and monitoring of the plantstatus can be made, and an alarmraised for any discrepancy conditionsbetween the open and closed auxiliarycontacts of the isolators and circuitbreakers.
Local communications port
All the relays are equipped with a localcommunications port on the front face.The PUs are also accessible from onecentral point via the protectioncommunication channel, i.e. via theP741 Central Unit.
The local communication port is
designed to be used with MiCOM S1. Itdeals with the local functions and allowsthe user to program bay settings and toconfigure the PSL. Extraction and
viewing of events, disturbance recordingand the fault records is also possible.
Supervision & diagnostics
Continuous self monitoring Continuous local supervision of
current transformers by zero-sequence current control
Continuous central supervision ofcurrent circuits by measurement of thedifferential current(circuitry fault detection)
Trip circuit supervision(using specific PSL)
Power-up diagnostics Test facilities
Diagnostics
Continous self-checking gives a high
degree of reliability. The results of theself-test functions are saved in thebattery-backed memory.The test features available on the userinterface provide the status of the inputquantities, the digital inputs, the relayoutputs and selected internal logic.
A local monitor port providing digitaloutputs, selected from a prescribed listof signals, including the status ofprotection elements may be used inconjunction with test equipment.
Hardware description
All models within the MiCOM P740series relays include: A back-lit liquid crystal display 12 LEDs Optional IRIG-B port (CU), RS232 Port, Fibre optic connection from
the CU to the PUs, Download/monitor port, Battery (supervised), N/O and C/O watchdog contacts Supervised +48 V field voltage
Dual rated CT inputs 1A/5A
The hardware variation between theMiCOM P740 series relay models are:
(1) Universal voltage range opto-inputs(2) N/O: Normally Open
C/O: Change Over
The opto inputs are independent, andmay be energised from any substationbattery voltage, or from the 48V-field
voltage.
User interface
The front panel user interface comprises:
(1) A 2 x 16 characters backlitLCD display(2) Four fixed LEDs(3) Eight user programmable LEDs(4) Menu navigation and data
entry keys(5) READ and CLEAR keys
to view alarms(6) An upper cover identifying
the product name.(7) A lower cover concealing the front
RS232 port & parallel port -download/monitoring port andbattery compartment.
(8) Facility for fitting a security
lead seal
5
P741 P742 P743
Relay
Outputs (2)
Opto
-inputs (1)8 16 24
6 N/O 6 N/O 15 N/O
2 C/O 2 C/O 6 C/O
12
3
4
5
6
78
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The user interface and menu text areavailable in English, French, German
and Spanish as standard. Labelssupplied with the device allow tocustomise the LEDs descriptions.
A user selectable default displayprovides measurement information,time/date, protection functions andplant reference information. The abilityto customise the menu text and alarmtext is also supported.
> Password Protection
Password protection may beindependently applied to the front userinterface, to the front communicationsport and to the rear communicationport. Two levels of password protectionare available providing access to thecontrols and settings respectively.
Software support
WindowsTM 98/ME/2000/NT compatible.MiCOM S1 software which comprises:
Settings editor Programmable Scheme Logic editor Menu text editor Display of fault diagnostics and
measurements Disturbance recorder viewer
Technical data
> Nominal Operating time
Typic 15 ms to energisation of CB tripcoil (including relay contact closure).
> Ratings
> Inputs
AC Current (In)
1 A / 5 A Dual rated
Frequency 50/60 Hz 5Hz
Auxiliary Voltage (Vx)
> Outputs
Field Voltage 48 Vdc
(current limit: 112 mA)> Optocoupled digital inputs
Maximum voltage input
(any setting): 300V dc
> Burdens
> P741
With 8 comms. boards
37 to 41 W
With 5 comms. boards
25 to 29 W
> P742: 16 to 23 W
> P743: 22 to 32 W
> Optical fibre connection
850nm, ST connectors Multi-mode fibre 62.5/125
Data rate: 2.5 Mbits
Maximum lenght: 1000 m
> Front communication port
Multi core Cable 15 m maxi.
Connector RS232 DTE
9 pins D-type Female
Protocol Courier
Isolation ELV for local access
> IRIG-B Port
Carrier signal
Amplitude modulated
Connection BNC
50 coaxial cable
> Download/monitor port
This is a 25 pin D-type female connector
located on the front user interface and is
specially designed for test purposes and
software download.
> Internal Battery
Battery type: AA, 3.6V
6
A = Clearance holesB = Mounting holes
23.25
159.00
10.30
168.0
0
177.00
Front view
Side view30.00
240.00Incl. wiring
Secondary cover (when fitted)
116.55 142.45
155.40 129.50305.50
A B A B B A
A B B AB A
12 off holes Dia. 3.4
303.50
309.60
157.5 max
177.0(4U)
483 (19 rack)
Sealingstrip
All dimensions in mm
CC CA
Operating range (V)
24 - 48 19 - 65 -
48 - 110 37 - 150 24 - 110
110 - 250 87 - 300 80 - 265
Nominal
(V) DC
>
Figure 4 Case size MiCOM P741 (80TE)
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7
7
Central Unit (CU)
Vx aux rating
Communication boards
Hardware options
1
24 - 48Vdc
48 - 125Vdc (30 - 100Vac)
110 - 250Vdc (100 - 240Vac)
1 communication board (up to 4 peripheral units)2 communication boards (up to 8 peripheral units)
Standard version 1IRIG-B input 2
3 communication boards (up to 12 peripheral units)4 communication boards (up to 16 peripheral units)
5 communication boards (up to 20 peripheral units)6 communication boards (up to 24 peripheral units)7 communication boards (up to 28 peripheral units)8 communication boards (up to 32 peripheral units)
1
2
3
1
MiCOM P 4
P741:
23
4
5678
A 1A 0 0* **
Central Unit,8 opto inputs, 8 outputs,Size 16" case (80 TE)
Information required with order
Peripheral Units (PU)
Vx aux rating
In rating
2
24 - 48Vdc
48 - 125V dc (30 - 100V ac)
110 - 250Vdc (100 - 240Vac)
1
2
3
Peripheral Unit,16 opto inputs, 8 outputs,Size 8" case (40 TE)
Peripheral Unit,24 opto inputs, 21 outputs,Size 12" case (60 TE)
3
P742:
P743:
1 & 5 A - 1 1 0 V 1
Without analogue inputs 0
7MiCOM P 4 A 1 * *0A1
23.30 155.40
181.30202.00
10.35
159.00 168.00
8 off holes Dia. 3.4
A B B A
A B B A
Flush mounting panel
Note: If mounting plateis required use flushmounting cut out dimensions
200.00
All dimensions in mm
Front view
177.00
206.00 30.00Side view
240.00Incl. wiring
Secondary cover (when fitted)
157.5 max
177.0(4U)
483 (19"rack)
Sealing strip
Panel cut-out detailA = Clearance holesB = Mounting holes
A = Clearance holesB = Mounting holes
23.25
159.00
10.30
168.0
0
177.00
Front view
Side view30.00
240.00Incl. wiring
Secondary cover (when fitted)
116.55 142.45
155.40 129.50305.50
A B A B B A
A B B AB A
12 off holes Dia. 3.4
303.50
309.60
157.5 max
177.0(4U)
483 (19 rack)
Sealingstrip
All dimensions in mm
> Case
The MiCOM relays are housed in aspecially designed case providing ahigh density of functionality within theproduct, a customisable user interface,and additional functions/informationconcealed by upper an lower covers.
Physical protection of the front paneluser interface and prevention of casualaccess is provided by an optionaltransparent front cover, which can befitted or omitted according to choicesince the front panel has been designed
to IP52 protection against dust andwater.
The case is suitable for either rack orpanel mounting as shown in figures4,5 and 6.
> P741 MiCOM 80TE
> P742 MiCOM 40TE
> P743 MiCOM 60TE
> Weight
P741(with 8 comms. boards):
7.6 kg
P741
(with 1 comms. board):
6.2 kg
P742
7.5 kg
P743
9.2 kg
>
Figure 5 Case size MiCOM P742 (40TE) Figure 6 Case size MiCOM P743 (60TE)
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ALSTOM Track Record -
Busbar protection
>> Low impedance biased differentialbusbar protection (MBCZ)launched in 1988.Over 6.522 units delivered.
>> Over 211 medium impedancebiased differential busbarprotection (DIFB) delivered sincelaunching in 1992.
>> Medium impedance biaseddifferential busbar protection withlinear current combination
(DIFB CL). Over 73 cubiclesdelivered since 1996.
Our policy is one of continuous development. Accordingly the design of our products may change at any time.Whilst every effort is made to produce up to date literature, this brochure should only be regarded as a guide and is intended for
information purposes only. Its contents do not constitute an offer for sale or advise on the application of any product referred to in it.We cannot be held responsible for any reliance on any decisions taken on its contents without specific advise.
South East Asia
Tel.: +65 67 49 07 77 - Fax: +65 68 41 95 55
Pacific
Tel.: +65 67 49 07 77 - Fax: +65 68 46 17 95China
Tel.: +86 10 64 10 62 88 - Fax: +86 10 64 10 62 64
India
Tel.: +91 11 26 44 99 07 - Fax: +91 11 26 44 94 47
North America
Tel.: +1 (484) 766-8100 - Fax: +1 (484) 766-8150
Central America
Tel.: +52 55 11 01 07 00 - Fax: +52 55 26 24 04 93
South America
Tel.: +55 11 30 69 08 01 - Fax: +55 11 30 69 07 93
France
Tel.: +33 1 40 89 66 00 - Fax: +33 1 40 89 67 19
British Isles
Tel.: +44 (0) 1785 27 41 08 - Fax: +44 (0) 1785 27 45 74
Northern Europe
Tel.: +49 69 66 32 11 51 - Fax: +49 69 66 32 21 54
Central Europe & Western Asia
Tel.: +48 22 850 96 00 - Fax: +48 22 654 55 90
Near & Middle East
Tel.: +971 6 556 3971 - Fax: +971 6 556 5133
Mediterranean, North & West Africa
Tel.: +33 1 41 49 20 00 - Fax: +33 1 41 49 24 23
Southern & Eastern Africa
Tel.: +27 11 82 05 111 - Fax: +27 11 82 05 220
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PAPERRTS
CTS
0V
RX
TX
SERIALPORT
8
9
7
4
6
5
3
2
CONNECTED
DATA READY
TO-T7
DO-D7
0V
RESETEXTERNAL
ACKNOWLEDGE
DOWNLOADCOMMAND
DATA
DOWNLOADTEST/
17
20,21,23,2411,12,15,13,
19,18,22,25
NOT
1 SK1
14
2-9
16
10
1
E16SCN
E18
SK2
E17
C9
OPTO 5 C10
OPTO 3
OPTO 4
OPTO 1
OPTO 2
C8
C7
C6
C5
C4
C3
C1
C2
A18
A16
A17
A15
A14
A12
A13
A10
A11
A7
A8
A9
A6
A5
C14
A4
A3
A2
A1
C17
C18
C16
C15
C12
C13
C11
CONNECTION
OPTO 16
COMMON
OPTO 15
OPTO 14
OPTO 13
OPTO 12
OPTO 11
OPTO 7
OPTO 10
OPTO 9
CONNECTIONCOMMON
OPTO 8
OPTO 6D8
D7
D10
D9
D12
D11
D13
D16
D18
D17
D14
D15
WATCHDOG
WATCHDOG
D2
D5
D6
D4
D3
E13
E14
D1
E12
E11
48V DC FIELDVOLTAGE OUT
-
-
+
+
+
-
E10
E9
E8
E2
E7
E1
COMMUNICATIONFIBRE OPTIC
CURR DIFF
RX2
RX1
TX2
TX1
CASEEARTH
DIRECTION OF FORWARD CURRENT FLOW
NOTE 2.
C
B
AS2 S1
P2 P1
NI
B12
B11
B10
B9
1A
5A
1A
B5
CI
B8
B6
B7
BI
B4
B3
B2
5A
1A
5A
1A
PHASE ROTATION
A
C B
I A
B1 5A
AUX SUPPLYAC OR DC Vx
MiCOM P742 (PART)
MiCOM P742 (PART)
POWER SUPPLY VERSION 24-48V (NOMINAL) D .C. ONLY*
CONTACT
CONTACT
RELAY 8
RELAY 7
RELAY 6
RELAY 5
RELAY 4
TRIP A
TRIP B
TRIP C
EIA485/KBUS
PORT
Busbar protectionPeripheral UnitP742
C.T. SHORTING LINKS
50 OHM BNC CONNECTOR
PIN TERMINAL (P.C.B. TYPE)
9-WAY & 25-WAY FEMALE D-TYPE SOCKET ANSI31_7
(b)
1.
NOTES
(a)
2.C.T. CONNECTION S ARE SHOWN 1ACONNECTED AND ARE TYPICAL ONLY.
3. THIS RELAY SHOULD BE ASSIGNED TOANY TRIP TO ENSURE CORRECT
OPERATION OF THE PROTECTIVE RELAY.
4. OPTO INPUTS 1 & 2 MUST BE USED FORSETTING GROUP CHANGES IF THIS OPTION
IS SELECTED IN THE RELAY MENU.
Figure 7 System overview of the P742 relay