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
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.
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)
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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
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.
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
BB4 P740 scheme applied for protecting double busbar with transfer bus
Transfer Bus 2 P742 or 2 P743
PROTECTION FUNCTIONS OVERVIEW
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)
Dead zone protection (short zone between CTs and CBs)
Current transformer supervision
Breaker failure protection (LBB)
• • •
• • • •
87BB / P 87BB / N
Isolator discrepancy alarm
Fibre optic signalling channel Digital inputs Output relays Front communication port (RS232)
• • • •
Rear communication port (RS485) Time synchronisation port (IRIG-B) * * Refer data sheet for model selection
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
Fibre optic signaling channel
Remote comm. port
Measurements Self monitoring
Binary Input / output
Fibre optic signaling channel
Remote comm. port
Busbar protection scheme Central Unit P741
Binary Input / output
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)
Operating current :
i diff (t)
Restraining current :
i bias(t) = i 1
i bias (t)
i diff node (t)
I D> 2 Is I D> 1
Differential current : i diff node (t)= i 1 +
i3 + ....... + i n Σ i3
i + ....... +
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:
SEF Block threshold
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.
> Magnitude criteria; confirmation of two simultaneous thresholds per zone: • Exceeding the bias slope characteristic (k) • Exceeding differential operating current threshold (ID>2).
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
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).
Dead zone protection
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
(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)
> 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
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.
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 (
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
BB4 Transfer Bus Figure 1
2 P742 or P743 P742
Double Busbar with transfer bus
Main protection functions
> 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
Sensitive earth fault busbar protection Check zone element (Supervision)
Phase Overcurrent protection
Earth Overcurrent protection
Current transformers supervision
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)
Figure 2 Bias characteristic
Differential current : idiff node (t) =
Restraining current :
i bias (t) = i 1
i bias (t)
i diff (t) = idiff node (t) +
ID > 2 Is ID > 1
Operating current :
+ i3 + ....... + i n = +
+ ....... +
> Dual characteristics
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
Opto -inputs (1)
Relay Outputs (2)
6 N/O 15 N/O
2 C/O 6 C/O
(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.
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.
The front panel user interface comprises:
(5) (6) (7)
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
142.45 A B
129.50 155.40 305.50 303.50
12 off holes Dia. 3.4 BA
483 (19" rack) A = Clearance holes B = Mounting holes
All dimensions in mm
Secondary cover (when fitted) 240.00 Incl. wiring
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)
> 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)
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
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 • 50Ω 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
> Burdens • • • •
• • • •
> P742: 16 to 23 W > P743: 22 to 32 W
> Internal Battery Battery type:
½ AA, 3.6V
8 off holes Dia. 3.4
155.40 A B
142.45 A B
483 (19" rack) A = Clearance holes B = Mounting holes
Note: If mounting plate is required use flush mounting cut out dimensions
129.50 155.40 305.50
Flush mounting panel Panel cut-out detail
A = Clearance holes B = Mounting holes 200.00
12 off holes Dia. 3.4 168.00
All dimensions in mm
All dimensions in mm Secondary cover (when fitted) 240.00 Incl. wiring
Secondary cover (when fitted) 240.00 Incl. wiring
177.00 157.5 max
Case size MiCOM P742 (40TE)
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
> 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
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
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
Busbar protection Peripheral Unit P742
S1 C B PHASE ROTATION
MiCOM P742 (PART) E11 E13
MiCOM P742 (PART) 5A
A3 A4 A5 A6
A11 A12 A13
+ + +
+ + + + + + + +
D5 TRIP C
D9 RELAY 5
COMMON CONNECTION -
E16 SCN C11
FIBRE OPTIC COMMUNICATION CURR DIFF
AC OR DC AUX SUPPLY
+ + -
48V DC FIELD VOLTAGE OUT
NOTES 1. (a)
C.T. SHORTING LINKS
PIN TERMINAL (P.C.B. TYPE)
50 OHM BNC CONNECTOR 9-WAY & 25-WAY FEMALE D-TYPE SOCKET ANSI31_7
C.T. CONNECTIONS ARE SHOWN 1A CONNECTED AND ARE TYPICAL ONLY.
THIS RELAY SHOULD BE ASSIGNED TO ANY TRIP TO ENSURE CORRECT OPERATION OF THE PROTECTIVE RELAY.
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
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.
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.
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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