Chap15-232-253

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Page 251

Feeder 1

Feeder 2

CT

CT
PU

CB

PU

CB

CT
PU

CB

CT
CB

Fibre optic link

Personal
Computer

PU
Central Unit
CU

System Communication Network

PU: Peripheral Unit
CU: Central Unit
Figure 15.20: Architecture for numerical protection scheme

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 has
been 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 the
units 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

Network Protection & Automation Guide

d. dead zone protection

In addition, monitoring functions such as CB and isolator
monitoring, disturbance recording and transformer
supervision are provided.
Because of the distributed topology used,
synchronisation of the measurements taken by the
peripheral 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 the
synchronisation signal, the high stability of the oscillator
in 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 transmission
to the central unit. Modelling of the CT response is
included, to eliminate errors caused by effects such as CT
saturation. Disturbance recording for the monitored
feeder is implemented, for later download as required.
Because each peripheral unit is concerned only with an
individual 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 to
calculating the sum of the measured currents, the
algorithm can also evaluate differences between
successive current samples, since a large change above a
threshold may indicate a fault the threshold being
chosen such that normal load changes, apart from inrush
conditions do not exceed the threshold. The same

251

Busbar P rotection

1 5 . 10 N U M E R I C A L B U S B A R P R OT E C T I O N
SCHEMES

15

Chap15-232-253

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Page 252

considerations can also be applied to the phase angles of

currents, and incremental changes in them.
One advantage gained from the use of numerical
technology is the ability to easily re-configure the
protection to cater for changes in configuration of the
substation. For example, addition of an extra feeder
involves the addition of an extra peripheral unit, the
fibre-optic connection to the central unit and entry via
the MMI of the new configuration into the central unit.
Figure 15.21 illustrates the latest numerical technology
employed.

In contrast, modern numerical schemes are more

complex with a much greater range of facilities and a
much high component count. Based on low impedance
bias techniques, and with a greater range of facilities to
set, setting calculations can also be more complex.
However, studies of the comparative reliability of
conventional high impedance schemes and modern
numerical schemes have shown that assessing relative
reliability is not quite so simple as it might appear. The
numerical scheme has two advantages over its older
counterpart:
a. there is a reduction in the number of external
components such as switching and other auxiliary
relays, many of the functions of which are
performed internally within the software
algorithms

15.10.1 Reliability Considerations

In considering the introduction of numerical busbar
protection schemes, users have been concerned with
reliability 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 and
has few components. Calculation of stability limits and
other setting parameters is straightforward and scheme
performance can be predicted without the need for
costly testing. Practically, high impedance schemes have
proved to be a very reliable form of protection.

Reliability analyses using fault tree analysis methods

have examined issues of dependability (e.g. the ability to
operate when required) and security (e.g. the ability not
to provide spurious/indiscriminate operation). These
analyses have shown that:

Busbar P rotection

b. numerical schemes include sophisticated

monitoring features which provide alarm facilities
if the scheme is faulty. In certain cases, simulation
of the scheme functions can be performed on line
from the CT inputs through to the tripping outputs
and thus scheme functions can be checked on a
regular basis to ensure a full operational mode is
available at all times

a. dependability of numerical schemes is better than

conventional high impedance schemes
b. security of numerical and conventional high
impedance schemes are comparable
In addition, an important feature of numerical schemes
is the in-built monitoring system. This considerably
improves the potential availability of numerical schemes
compared to conventional schemes as faults within the
equipment and its operational state can be detected and
alarmed. With the conventional scheme, failure to reinstate the scheme correctly after maintenance may not
be detected until the scheme is required to operate. In
this situation, its effective availability is zero until it is
detected and repaired.

15

1 5 . 11 R E F E R E N C E S
15.1 The Behaviour of Current Transformers subjected
to Transient Asymmetric Currents and the
Effects on Associated Protective Relays. J.W.
Hodgkiss. CIGRE Paper Number 329, Session
15-25 June 1960.

Figure 15.21: Busbar protection relay using the

latest numerical technology (MiCOM P740 range)

252

Network Protection & Automation Guide

P R OT E C T I O N

MiCOM P740
Numerical Busbar Protection

The MiCOM P740 numerical busbar protection

scheme provides complete protection for all
types of extra / ultra high voltage busbar
configurations.

MiCOM P741 in 80TE

MiCOM P743 in 60TE

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.

MiCOM P742 in 40TE

Customer benefits
Fast fault trip
(typically 15ms)
Adaptable to any busbar
configuration.
Can operate with different
types of CT.
Fibre optic cable used for
communication between
Central and Peripheral Units:
- Ensures high
communication speed
- Eliminates insulation
problems

AREVA T&D

The MiCOM P740 busbar differential protection

scheme can be engineered to provide a
centralized or a distributed architecture. It also
supports easy maintenance, operation and future
expansion of the busbar.

APPLICATION

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 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 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.

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
BB1

BB3

BB2

BB4
P740 scheme
applied for protecting
double busbar with transfer bus

Transfer
Bus
2 P742 or
2 P743

P742

P743

Peripheral Units

Optical fibre

P741

P742

P743

Central Unit

Peripheral Units

PROTECTION FUNCTIONS OVERVIEW

P741

P742

P743

87 CZ

Phase segregated biased current

differential high speed busbar protection
Sensitive earth fault bias current controlled
busbar protection
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)

Current transformer supervision

50BF

Breaker failure protection (LBB)

CTS

87BB / P
87BB / N

ISL

Isolator discrepancy alarm

Fibre optic signalling channel

Digital inputs
Output relays
Front communication port (RS232)

8
8

16
8

24
21

option

Rear communication port (RS485)

Time synchronisation port (IRIG-B) *
* Refer data sheet for model selection

2>3

Complete flexibility to suit

any busbar configuration

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

FUNCTIONAL OVERVIEW

Fibre optic
signaling
channel

Remote
comm. port

Local
Communication

Fault records

Disturbance
Record

Measurements
Self monitoring

87BB
/N

87BB
/P

/
X

Binary
Input / output

Fibre optic
signaling
channel

50BF

87CZ

Remote
comm. port

CTS

LEDs

PSL

Local
Communication

50S T

Busbar protection scheme

Central Unit P741

Fault records

Disturbance
Record

Measurements

Self monitoring

50/
51/P

50/
51/N

Binary
Input / output

50BF

PSL

CTS

LEDs

ISL

Busbar protection scheme

Peripheral Unit P742 / P743

(Description of ANSI code nos. see Protection Function Overview)

Speed, Sensitive & Secure:

P740 the ultimate in busbar protection

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.

CT saturation detection

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.

Universal on-line topology processing

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.

Bias differential characteristics

i diff (t)

i1

o
0t

i2
i3

k
s-

in

Operating current :

i diff (t)

Restraining current :

i bias(t) = i 1

rc
pe

i2

90

=2

bia

Restrain
area

i bias (t)

2 +

i diff node (t)

e
tag

en

I D> 2
Is
I D> 1

Differential current : i diff node (t)= i 1 +

4>5

Tripping
Area

=
+

i3 + ....... + i n

i3

i
+ ....... +

in

DUAL CHARACTERISTICS

idiff
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.

Trip
rc
Pe

ID>2
IS
ID>1

Any tripping order must therefore be made conditional

on the simultaneous occurrence of 5 or 6 criteria:

ibias
Enable

Block

SEF Block threshold

idiff

Trip
bia s ntage
Perce

IDN >2
ISN
IDN >1

> 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 trip confirmation.

kN

Restrain

kNmin =0.2

ibias

> Magnitude criteria; confirmation of two simultaneous

thresholds per zone:
Exceeding the bias slope characteristic (k)
Exceeding differential operating current threshold
(ID>2).

-k

Restrain

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.

s
bia
ge
a
t
en

Dual characteristics

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

> 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.

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.

DEAD ZONE OR BLIND SPOT

PROTECTION
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.

ADDITIONAL ULTRA HIGH SPEED

EXTERNAL 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).

BB1

Dead zone protection

CB Closed

CB Open

Dead Zone

PU1
connected
to BB1

PU2 not connected to BB1

= Activation
of Dead Zone protection

Intertrip contact
to other end

PHASE OVERCURRENT AND

EARTH FAULT PROTECTION

ISOLATION AND MAINTENANCE

OPERATING MODE

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:

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.

> 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

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

time.

(measurements active and tripping deactivated). The

Breaker Failure protection remains operational.
CIRCUIT BREAKER FAILURE
PROTECTION (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 TRANSFORMER
MISMATCH 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).

Programmable scheme
logic editor (MiCOM S1)

6>7

> 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 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.

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.

MEASUREMENT
AND 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.

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)

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.

> 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

Device Track Record

LOCAL AND REMOTE
COMMUNICATIONS
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).

>> 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.

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),

DIAGNOSTICS
Automatic tests performed including power-on diagnostics and
continuous 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.

> 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.

AREVA T&D Worldwide Contact Centre:

http://www.areva-td.com/contactcentre/
Tel.: +44 (0) 1785 250 070

www.areva-td.com
www.areva-td.com/protectionrelays

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 advice.

AUTOMATION-L3-P740-BR-05.05-1021-GB - - AREVA - 2004. AREVA, the AREVA logo and any alternative version thereof are trademarks and service marks of AREVA. MiCOM is a registered trademark of AREVA. All
trade names or trademarks mentioned herein whether registered or not, are the property of their owners. - 389191982 RCS PARIS - Printed in France - SONOVISION-ITEP

The default remote communications is Courier / K-bus and can

be converted to IEC60870-5-103.

MiCOM P740

>

Our products

Numerical Busbar Protection

>

Customer benefits
This architecture can
accommodate the most
complex substation layouts
and different CT classes
and manufacturers.
The use of fibre optics for
communication between
Peripheral Units and the
Central Unit gives the
following advantages:
- High communication
speed
- Eliminates insulation
problems
Fast fault clearance
(Typical tripping time 15 ms).

>> The consequences of a fault

on the busbars of a power
transmission or distribution
network substation may be very
serious. Poor quality of supply to
consumers and damage to the
electrical equipment are very
real threats.

ALSTOM has developed a new

and fully numerical busbar
protection. The primary
objectives are to provide total
protection stability under normal
operating conditions and for all
external faults, whilst reacting
quickly to internal faults. This
protection scheme is the
MiCOM P740.
The MiCOM P740 provides
high-speed protection (<1 cycle)
which meets the requirements of
the most demanding
specifications for extra high
voltage transmission networks.
The MiCOM P740 differential
busbar protection protects
configurations up to 8 zones
and 32 feeders. Its architecture
may be centralised in one
cubicle, or distributed around the
substation.

>

>

Key features
> 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 separate
element 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.

T&D
Energy Automation & Information

BB1

BB3

BB2

BB4
Transfer
Bus
Figure 1

2 P742
or
P743
P742

P743

Peripheral Units

Optical Fibre

P741

Double Busbar
with transfer bus

Central
Unit

Main protection functions

P742

P743

Peripheral Units

> Universal topological

processing algorithms

> Architecture
The architecture of the numerical
differential busbar protection is built
around a P741 Central Unit (CU) which
gathers and processes all the analogue
measurements from the P742 and P743
Peripheral Units (PU) via direct fibre
optic 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

The MiCOM P740 uses new universal

algorithms based on operational
research which create, in real time,
architectures of up to 8 zones.
> Stabilisation against
CT saturation
One of the most important objectives of
a differential busbar protection is to
ensure stability when CTs become
saturated, particularly under external
fault conditions.
In order to avoid this risk of
maloperation, the MiCOM P740 uses
innovative ultra high-speed algorithms
based on signal consistence variation
model (registered patent).

Breaker Fail protection

(general 3 poles trip).

> Bias characteristic

The operation of the MiCOM P740 is
based on an algorithm with a
characteristic (see figure 2) in which the
differential current is compared with a
bias value.
The purpose of this characteristic is to
ensure the stability of the protection
when there is an external fault, differing
CT tolerances and errors which
otherwise would lead to spurious
detection of an in-zone fault.
> Global supervision by
check zone element
One of the most frequent causes of the
maloperation of busbar protection
schemes is an error in actual plant
status. This leads to the production of a
differential current.

Models available
> 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 is

based on the numerical application of
Kirchoff's Law for the selective detection
and ultra high-speed isolation of a
faulty section of a busbar.

Features
Central
Unit
Peripheral
Unit

8 Opto Universal Inputs, 8 Output relays

(MiCOM 16 case, 80 TE)
16 Opto Universal Inputs, 8 Output relays
(MiCOM 8 case, 40 TE)

P741 P742 P743

24 Opto Universal Inputs, 21 Output relays

(MiCOM 12 case, 60 TE)
Phase segregated current
differential busbar protection

87BB/N
87CZ

Sensitive earth fault busbar protection

Check zone element (Supervision)

50/51/P

Phase Overcurrent protection

50/51/N

Earth Overcurrent protection

CTS

Current transformers supervision

50BF

Breaker fail protection

Local single or

Peripheral
Unit
87BB/P

three pole re-trip

General three pole

back-trip

Fibre Optic signalling channels

However, if all currents of the whole

substation are taken into account, their
sum will remain null if a fault is not
present, irrespective of the error in plant
status/position.
Consequently, the tripping order for a
zone element is conditional on the
operation of a check zone element.
The main advantage of this element is
the total insensitivity to defective
auxiliary contacts.
> Dead zone or Blind spot
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
automatically created between the CB
and the associated CT.
> Continuous supervision of the
current circuits by
measurement of the
differential current value
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>2 which is set above the highest load
current.
> Stabilisation of the protection
in the event of CT saturation
for external fault
One main quality of the MiCOM P740
is its ability to detect CT saturation in
less than 2 ms.
The signal processing algorithms
implemented in the MiCOM P740
combine a simulation of the flux built up
in the core of the CTs with a recursive
consistence variation control
(registered patent).
> Additional ultra high speed
external 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).

i diff (t)

Tripping
Area

Figure 2
Bias
characteristic

i1

i2
i3

ias

eb

in

Differential current : idiff node (t) =

i1

Restraining current :

i bias (t) = i 1

i2

90

i bias (t)

i2

i diff (t) = idiff node (t)

+

pe

-k

to

Restrain
area

rce

ID > 2
Is
ID > 1

Operating current :

g
nta

0
=2

+ i3 + ....... + i n
=
+

i
i3

+ ....... +

in

> Dual characteristics

Additional protection

The MiCOM P740 offers phasesegregated protection and a separate

element for earth fault detection.

The following back-up protection

functions are implemented locally in the
Peripheral Units (P742/P743).

> Multiple tripping criteria

> Phase and Earth Fault

overcurrent protection either
Definite Time (DT) or IDMT
(IEC/UK, IEEE/US curves)

The MiCOM P740 maintains the highest

level of stability, under all conditions
including:
> 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 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
No discrepancy detected.
> 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 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 is
confirmation by local overcurrent
criteria.

Two independent stages are available

for 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 Failure
protection from the busbar
protection system
The usual 50 BF relay is totally
independent of the others and the
control connection with the busbar
protection system is hardwired. Receipt
of an external 50BF information results
in tripping of all the adjacent circuit
breakers, via the topological recognition
system knowing which breaker is
connected to which zone.
> Internal breaker failure
protection in the busbar
protection system
Some operators prefer an integrated
solution, which 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.

Figure 3
Programmable Scheme Logic

Matching CT Transformer ratios

> Balancing protection
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.
> Common base ratio
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 CU are all adjusted to this
common current, known as the primary
basis current (Ibp).

> 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 be
applied 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
Isolation and downgraded
operating 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.
> Central Unit - CU (P741)

A central command to isolate the

busbars at two levels can be applied
selectively zone by zone.
> Differential protection (87 BB) in
monitoring mode (measurements
active and tripping deactivated).
The Breaker Failure protection
remains operational.

> Circuit breaker control

The circuit breaker control is available
from the front panel user interface, or
the optically isolated inputs.
> Programmable scheme logic
Powerful Programmable Scheme Logic
(PSL) allows the user to customise the
protection and control functions. It is
also used to program the functionality of
the optically isolated inputs, relay
outputs and LED indications.
The PSL uses up to 256 logic gates and
8 timers and is configured using the
graphical MiCOM S1 PC based
software as illustrated in Figure 3.

> Independent protection

settings groups
The settings are divided into two
categories: protection settings and
control and configuration settings. Four
settings groups are provided for the
protection settings to allow different
operating conditions and adaptive
relaying.

Measurement and 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 IRIG-B port
is also provided for accurate time
synchronisation.
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.
> 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 current
IN
Frequency
f

Post fault analysis

Local communications port

> Event recorder

All the relays are equipped with a local

communications port on the front face.
The PUs are also accessible from one
central point via the protection
communication channel, i.e. via the
P741 Central Unit.

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.
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 stores
on 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)

The local communication port is

designed to be used with MiCOM S1. It
deals with the local functions and allows
the user to program bay settings and to
configure the PSL. Extraction and
viewing of events, disturbance recording
and the fault records is also possible.

The hardware variation between the

MiCOM P740 series relay models are:

Supervision & diagnostics

Continuous self monitoring
Continuous local supervision of
current transformers by zerosequence current control
Continuous central supervision of
current circuits by measurement of the
differential current
(circuitry fault detection)
Trip circuit supervision
(using specific PSL)
Power-up diagnostics
Test facilities

Diagnostics

P741

P743

Opto
-inputs (1)

Relay
Outputs (2)

6 N/O

6 N/O 15 N/O

2 C/O

2 C/O 6 C/O

16

24

(1) Universal voltage range opto-inputs

(2) N/O: Normally Open
C/O: Change Over

The opto inputs are independent, and

may be energised from any substation
battery voltage, or from the 48V-field
voltage.

User interface
6

These records may be examined using

MiCOM S1 or COMTRADE viewer.

Continous self-checking gives a high

degree of reliability. The results of the
self-test functions are saved in the
battery-backed memory.
The test features available on the user
interface provide the status of the input
quantities, the digital inputs, the relay
outputs and selected internal logic.
A local monitor port providing digital
outputs, selected from a prescribed list
of signals, including the status of
protection elements may be used in
conjunction with test equipment.

Plant status

Hardware description

(1)

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.

All models within the MiCOM P740

series 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

(2)
(3)
(4)

Disturbance records can be extracted

from the relay via the remote
communications and saved in the
COMTRADE format.

P742

5
7

The front panel user interface comprises:

(5)
(6)
(7)

(8)

A 2 x 16 characters backlit
LCD display
Four fixed LEDs
Eight user programmable LEDs
Menu navigation and data
entry keys
READ and CLEAR keys
to view alarms
An upper cover identifying
the product name.
A lower cover concealing the front
RS232 port & parallel port download/monitoring port and
battery compartment.
Facility for fitting a security
lead seal

116.55

23.25

142.45
A B

159.00
AB

10.30

B A

177.0
(4U)

BA

129.50
155.40
305.50
303.50

Sealing
strip

12 off holes Dia. 3.4

BA

168.00

AB

483 (19" rack)

A = Clearance holes
B = Mounting holes

>

All dimensions in mm

Secondary cover (when fitted)

240.00
Incl. wiring

Front view

157.5 max

177.00

309.60

30.00

Side view

Figure 4

The user interface and menu text are

available in English, French, German
and Spanish as standard. Labels
supplied with the device allow to
customise the LEDs descriptions.
A user selectable default display
provides measurement information,
time/date, protection functions and
plant reference information. The ability
to customise the menu text and alarm
text is also supported.

> Password Protection

Password protection may be
independently applied to the front user
interface, to the front communications
port and to the rear communication
port. Two levels of password protection
are available providing access to the
controls and settings respectively.

Software support
WindowsTM 98/ME/2000/NT compatible.
MiCOM S1 software which comprises:

Case size MiCOM P741 (80TE)

Technical data

> Optical fibre connection

> Nominal Operating time

Typic 15 ms to energisation of CB trip
coil (including relay contact closure).

Settings editor
Programmable Scheme Logic editor
Menu text editor
Display of fault diagnostics and
measurements
Disturbance recorder viewer

> Front communication port

> Inputs
AC Current (In)
1 A / 5 A Dual rated
Frequency 50/60 Hz 5Hz
Auxiliary Voltage (Vx)
Nominal

Operating range (V)

(V) DC

CC

24 - 48
48 - 110
110 - 250

19 - 65
37 - 150
87 - 300

Multi core Cable 15 m maxi.

Connector RS232 DTE
9 pins D-type Female
Protocol Courier
Isolation ELV for local access

CA

24 - 110
80 - 265

> Outputs
Field Voltage 48 Vdc
(current limit: 112 mA)
> Optocoupled digital inputs
Maximum voltage input
(any setting): 300V dc

> 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.

> P741
With 8 comms. boards
37 to 41 W
With 5 comms. boards
25 to 29 W

850nm, ST connectors
Multi-mode fibre 62.5/125
Data rate: 2.5 Mbits
Maximum lenght: 1000 m

> Ratings

> Burdens

> P742: 16 to 23 W
> P743: 22 to 32 W

> Internal Battery

Battery type:

AA, 3.6V

8 off holes Dia. 3.4

155.40
A B

159.00
AB

Sealing strip

177.0
(4U)

168.00

116.55

23.25

BA

AB

142.45
A B

BA

159.00

BA

181.30
202.00

10.35

B A

BA

483 (19" rack)

A = Clearance holes
B = Mounting holes

303.50

Note: If mounting plate

is required use flush
mounting cut out dimensions

177.0
(4U)

129.50
155.40
305.50

10.30

Flush mounting panel

Panel cut-out detail

A = Clearance holes
B = Mounting holes
200.00

AB

483 (19"rack)

Sealing
strip

12 off holes Dia. 3.4

168.00

23.30

>

All dimensions in mm

All dimensions in mm
Secondary cover (when fitted)
240.00
Incl. wiring

Front view

Secondary cover (when fitted)

240.00
Incl. wiring

Front view

157.5 max

177.00
157.5 max

177.00

309.60
206.00

Figure 5

Case size MiCOM P742 (40TE)

> Case

Side view

30.00

Side view

30.00

Figure 6

Case size MiCOM P743 (60TE)

Information required with order

The MiCOM relays are housed in a

specially designed case providing a
high density of functionality within the
product, a customisable user interface,
and additional functions/information
concealed by upper an lower covers.
Physical protection of the front panel
user interface and prevention of casual
access is provided by an optional
transparent front cover, which can be
fitted or omitted according to choice
since the front panel has been designed
to IP52 protection against dust and
water.
The case is suitable for either rack or
panel mounting as shown in figures
4,5 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

MiCOM P 7 4

Central Unit (CU)

1

P741: Central Unit,

8 opto inputs, 8 outputs,
Size 16" case (80 TE)

Vx aux rating
24 - 48V dc
48 - 125V dc
110 - 250V dc

1
2
3

(30 - 100V ac)

(100 - 240V ac)

Communication boards
1
2
3
4
5
6
7
8

communication
communication
communication
communication
communication
communication
communication
communication

board
boards
boards
boards
boards
boards
boards
boards

(up to
(up to
(up to
(up to
(up to
(up to
(up to
(up to

1
2

4 peripheral units)
8 peripheral units)
12 peripheral units)
16 peripheral units)
20 peripheral units)
24 peripheral units)
28 peripheral units)
32 peripheral units)

4
5
6
7
8

Hardware options
Standard version
IRIG-B input

1
2

MiCOM P 7 4

Peripheral Units (PU)

P742: Peripheral Unit,
16 opto inputs, 8 outputs,
Size 8" case (40 TE)

P743: Peripheral Unit,

24 opto inputs, 21 outputs,
Size 12" case (60 TE)

Vx aux rating
24 - 48V dc
48 - 125V dc
110 - 250V dc

(30 - 100V ac)

(100 - 240V ac)

1
2
3

In rating
Without analogue inputs
1 & 5 A - 110 V

0
1

P2

Busbar protection
Peripheral Unit
P742

P1
S2

S1
C
B
PHASE ROTATION

MiCOM P742 (PART)

E11
E13

EIA485/KBUS

MiCOM P742 (PART)

5A

IA

C12
B2

NOTE 2.

B3
B4

C13

1A

C14

5A

C15

IB

C16

B5

B6
B7

1A

C17

5A

C18

IC

A1
B8

B9

A2
1A

A3
A4
A5
A6

B10

IN

A7

5A

A8
A9

B11

B12

A10

1A

A11
A12
A13

OPTO 1

OPTO 2

OPTO 3

OPTO 4

+
+

OPTO 5

A14

C1

A15

C2

A16

C3

+
+
+

E18

D1
D3

OPTO 8

TEST/
DOWNLOAD

+
+
+
+
+
+
+
+

D5
TRIP C

D6
D7

SK2

RELAY 4

D8

10

D9
RELAY 5

D10

16

D11

DOWNLOAD
COMMAND

17

DO-D7

2-9

D14

TO-T7

11,12,15,13,
20,21,23,24

D15

RELAY 6

D12
D13

NOT
CONNECTED

RELAY 7

D16
D17

19,18,22,25

0V

OPTO 9

TRIP B

D4

EXTERNAL
RESET

OPTO 7

TRIP A

D2

DATA
ACKNOWLEDGE

COMMON
CONNECTION
-

A18

C5

E17

DATA READY

OPTO 6

RELAY 8

D18

14

OPTO 10

OPTO 11

OPTO 12

OPTO 13

SERIAL
PORT

TX

1
2

RX

SK1

4
5

0V

6
CTS

PAPER
RTS

8
9

OPTO 14

TX1

OPTO 15

OPTO 16

A17

C4

E16
SCN
C11

WATCHDOG
CONTACT

E14

PORT

B1

WATCHDOG
CONTACT

E12

COMMON
CONNECTION

FIBRE OPTIC
COMMUNICATION
CURR DIFF

RX1

TX2

RX2

E1
E2

C6
C7

E7

C8

E8

C9

E9

C10

E10

AC OR DC
AUX SUPPLY

Vx

+
+
-

48V DC FIELD
VOLTAGE OUT

CASE
EARTH

NOTES
1.
(a)

C.T. SHORTING LINKS

(b)

PIN TERMINAL (P.C.B. TYPE)

50 OHM BNC CONNECTOR

9-WAY & 25-WAY FEMALE D-TYPE SOCKET ANSI31_7

2.

C.T. CONNECTIONS ARE SHOWN 1A

CONNECTED AND ARE TYPICAL ONLY.

3.

THIS RELAY SHOULD BE ASSIGNED TO

ANY TRIP TO ENSURE CORRECT
OPERATION OF THE PROTECTIVE RELAY.

4.

OPTO INPUTS 1 & 2 MUST BE USED FOR

SETTING GROUP CHANGES IF THIS OPTION
IS SELECTED IN THE RELAY MENU.

POWER SUPPLY VERSION 24-48V (NOMINAL) D.C. ONLY

Figure 7

System overview of the P742 relay

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 95
China
Tel.: +86 10 64 10 62 88 - Fax: +86 10 64 10 62 64

ALSTOM Track Record -

India
Tel.: +91 11 26 44 99 07 - Fax: +91 11 26 44 94 47

>> Low impedance biased differential

busbar protection (MBCZ)
launched in 1988.
Over 6.522 units delivered.

Busbar protection

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

>> Over 211 medium impedance

biased differential busbar
protection (DIFB) delivered since
launching in 1992.

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

>> Medium impedance biased

differential busbar protection with
linear current combination
(DIFB CL). Over 73 cubicles
delivered since 1996.

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

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.

www.tde.alstom.com

T&D/BPROB/MiCOMP740/us/EAI/11.03/FR/4882- - ALSTOM - 2003. ALSTOM, the ALSTOM logo and their frameworks are trademarks and service trademarks applications of ALSTOM.
MiCOM is a registered trademark of ALSTOM. The other names mentioned, registered or not, are the property of their respective companies. 389191982 RCS PARIS - 11.03.006/Db - SONOVISION-ITEP

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