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
S C H E M E S
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
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
•
15
•Busbar P
rot
ect
ion
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 CB PU 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
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.
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.
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
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
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:
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
re-instate 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.
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.
•
15
•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 the
latest numerical technology (MiCOM P740 range)
Busbar P
rot
ect
ion
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 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.
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
MiCOM P740
Numerical Busbar Protection
P R OT E C T I O NMiCOM P741 in 80TE
MiCOM P743 in 60TE
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.
Complete flexibility to suit
any busbar configuration
P740 scheme applied for protecting double busbar with transfer bus
BB1
Central Unit
Optical fibre Peripheral Units
Peripheral Units BB2 BB3 BB4 Transfer Bus 2 P742 or 2 P743 P742 P743 P741 P743 P742
PROTECTION FFUNCTIONS OOVERVIEW P741 P742 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 -
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. portBusbar protection scheme Peripheral Unit P742 / P743 LEDs Binary Input / output Self monitoring 50/ 51/P 50/ 51/N 50S T Disturbance Record Fibre optic signaling channel 50BF CTS Fault records Measurements PSL Local Communication Remote comm. port
Busbar protection scheme Central Unit P741 LEDs Binary Input / output Self monitoring 87BB / P 87BB / N 87CZ Disturbance Record Fibre optic signaling channel 50BF CTS ISL FUNCTIONAL OVERVIEW
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.
i (t)
biasI > 2
Di
3i
ni
2i
1I > 1
DI
spercentage bias - k = 20 to 90%
Tripping
Area
Restrain
area
i (t)
diff node Differential current : = +i
1 +i
2i
3+ ... +i
ni (t)
diff Operating current : = = ii (t)
diffi (t)
biasi
1i
2i
3i
n Restraining current : = + + + ... + =i
i (t)
diff nodeΣ
Σ
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.
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 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.
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.
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 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).
Dual characteristics
PU1 connected to BB1
PU2 not connected to BB1 = Activation
of Dead Zone protection
CB Open CB Closed Dead Zone BB1 Intertrip contact to other end I D>2
Trip
IS ID>1i
diff Perce ntage bias - k IDN>2Restrain
Trip
I IDN>1i
biasi
biasi
diff Percentage bias - kN SEF Block thresholdkNmin=0.2 Block
Enable
Restrain
SN
Programmable scheme logic editor (MiCOM S1)
PHASE OVERCURRENT AND EARTH 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 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).
ISOLATION AND MAINTENANCE 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.
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 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.
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.
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).
The default remote communications is Courier / K-bus and can be converted to IEC60870-5-103.
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.
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. 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.
A U T OMA TION-L3-P740-BR-05.05-1021-GB - © - AREV A - 2004. AREV A, the AREV A logo and an y alter nativ e v
ersion thereof are tr
ademar ks and ser vice mar ks of AREV A. MiCOM is a registered tr ademar k of AREV A. All tr ade names or tr ademar
ks mentioned herein whether registered or not, are the proper
ty of their o wners . - 389191982 RCS P ARIS - Pr inted in F rance - SONO VISION-ITEP
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
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.
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).
>
T&D
Energy Automation & Information
MiCOM P740
Numerical Busbar Protection
>>
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.
Our products
>
Main protection functions > 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
• 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 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.
> Universal topological processing algorithms
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).
> 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. 2 Models available
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Features
P741 P742 P743
Central Unit Peripheral Unit Peripheral Unit 87BB/P 87BB/N 87CZ 50/51/P 50/51/N CTS 50BF8 Opto Universal Inputs, 8 Output relays (MiCOM 16” case, 80 TE)
16 Opto Universal Inputs, 8 Output relays (MiCOM 8” case, 40 TE)
24 Opto Universal Inputs, 21 Output relays (MiCOM 12” case, 60 TE)
Phase segregated current differential busbar protection Sensitive earth fault busbar protection Check zone element (Supervision) Phase Overcurrent protection Earth Overcurrent protection Current transformers supervision Breaker fail protection
Local single or three pole re-trip General three pole back-trip
Fibre Optic signalling channels •
•
Figure 1 Double Busbar with transfer bus BB1
Central Unit
Optical Fibre Peripheral Units Peripheral Units BB2 BB3 BB4 Transfer Bus 2 P742 or P743 P742 P743 P741 P743 P742
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,
I
D>1, which can be set to alarm from 1% of the primary basis current (I
bp).> 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
I
D>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).
> Dual characteristics
The MiCOM P740 offers phase-segregated protection and a separate element for earth fault detection.
> Multiple tripping criteria
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 (
I
D>2).> Exceeding the supervision threshold (
I
D>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.
Additional protection
The following back-up protection functions are implemented locally in the Peripheral Units (P742/P743).
> Phase and Earth Fault overcurrent protection either Definite Time (DT) or IDMT (IEC/UK, IEEE/US curves)
Two independent stages are available for phase and earth:
> First stage (
I
>1 orI
N>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 orI
N>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. i (t)bias I > 2 D
i
3i
ni
2i
1 I > 1 D I s percentage bias - k = 20 to 90% Tripping Area Restrain area i (t)diff node Differential current : = +i 1 +i 2 i 3 + ... + i n i (t)diff Operating current : = = ∑ i i (t)diff i (t)bias i 1 i 2 i 3 i n Restraining current : = + + + ... + = ∑ i i (t)diff node 3 Figure 2 Bias characteristic4
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 (
I
bp).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.
> 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
> 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
I
diff/phase/zone • Bias CurrentI
bias/phase/zone • Check zoneI
diff/phase> Peripheral units (P742 & P743) • Phase currents
I
AI
BI
C • Neutral currentI
N • Frequency f Figure 3Post fault analysis > 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.
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)
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 COMTRADE viewer.
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.
Local communications port
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.
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.
Supervision & diagnostics
• Continuous self monitoring
• Continuous local supervision of current transformers by zero-sequence 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
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.
Hardware description
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
The hardware variation between the MiCOM 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, and may be energised from any substation battery voltage, or from the 48V-field voltage.
User interface
The front panel user interface comprises: (1) A 2 x 16 characters backlit
LCD 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 and battery 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
1 2 3 4 5 6 7 8
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
WindowsTM98/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 trip coil (including relay contact closure).
> Ratings > Inputs • AC Current (
I
n) 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
Ω
coaxial cable > Download/monitor portThis 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: ½ AA, 3.6V
6 A = Clearance holes B = Mounting holes 23.25 159.00 10.30 168.00 177.00 Front view Side view 30.00 240.00 Incl. wiring
Secondary cover (when fitted) 116.55 142.45
155.40 129.50 305.50
A B A B B A
A B B A B A
12 off holes Dia. 3.4
303.50 309.60 157.5 max 177.0 (4U) 483 (19" rack) Sealing strip 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
>
7 7
Central Unit (CU)
Vx aux rating Communication boards Hardware options 1 24 - 48V dc 48 - 125V dc (30 - 100V ac) 110 - 250V dc (100 - 240V ac)
1 communication board (up to 4 peripheral units) 2 communication boards (up to 8 peripheral units)
Standard version 1
IRIG-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: 2 3 4 5 6 7 8 A 1 A 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 - 48V dc 48 - 125V dc (30 - 100V ac) 110 - 250V dc (100 - 240V ac) 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 - 110 V 1
Without analogue inputs 0
7 MiCOM P 4 1 A 0 A 1 * * 23.30 155.40 181.30 202.00 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 plate is required use flush mounting cut out dimensions 200.00 All dimensions in mm Front view 177.00 206.00 30.00 Side view 240.00 Incl. wiring Secondary cover (when fitted)
157.5 max 177.0
(4U)
483 (19"rack) Sealing strip
Panel cut-out detail A = Clearance holes B = Mounting holes A = Clearance holes B = Mounting holes 23.25 159.00 10.30 168.00 177.00 Front view Side view 30.00 240.00 Incl. wiring
Secondary cover (when fitted) 116.55 142.45
155.40 129.50 305.50
A B A B B A
A B B A B A
12 off holes Dia. 3.4
303.50 309.60 157.5 max 177.0 (4U) 483 (19" rack) Sealing strip All dimensions in mm > Case
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
>
T&D/BPROB/M
iCOMP740/us/EAI/11.03/FR/4882
-
© - ALSTOM - 2003. ALSTOM, the ALSTOM logo and their frameworks are trademarks and se
rvice trademarks applications of ALSTOM.
MiCOM is a registered trademark of ALSTOM. The other names mentioned, registered or not, are the prope
rty of their respective c
ompanies. 389191982 RCS PARIS - 1 1 .03 .0 06 / Db - SONOVISION-ITEP www.tde.alstom.com
ALSTOM Track Record - Busbar protection
>> Low impedance biased differential
busbar protection (MBCZ) launched in 1988. Over 6.522 units delivered.
>> Over 211 medium impedance
biased differential busbar protection (DIFB) delivered since launching in 1992.
>> Medium impedance biased
differential busbar protection with linear current combination (DIFB CL). Over 73 cubicles delivered 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 95 China 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 + -+ + -+ -+ -+ -+ + -+ -+ -+ -+ + -+ -+ -+ -* + -PAPER RTS CTS 0V RX TX SERIAL PORT 8 9 7 4 6 5 3 2 CONNECTED DATA READY TO-T7 DO-D7 0V RESET EXTERNAL ACKNOWLEDGE DOWNLOAD COMMAND DATA DOWNLOADTEST/ 17 20,21,23,24 11,12,15,13, 19,18,22,25 NOT 1 SK1 14 2-9 16 10 1 E16 SCN 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 CONNECTION COMMON OPTO 8 OPTO 6 D8 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 FIELD VOLTAGE OUT -+ + + -E10 E9 E8 E2 E7 E1 COMMUNICATIONFIBRE OPTIC
CURR DIFF RX2 RX1 TX2 TX1 CASE EARTH
DIRECTION OF FORWARD CURRENT FLOW
NOTE 2. C B A S2 S1 P2 P1 N I B12 B11 B10 B9 1A 5A 1A B5 C I B8 B6 B7 B I 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 protection Peripheral Unit P742 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. 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.
