Transmission & Distribution
Putting substations through their PACIS2 January 2005
The most recent version of Areva’s PACiS substation automation system, working with the new IEC protocol, allows an unprecedented degree of inter-device co-operation.
PACiS – protection, automation and control integrated solution – is what Areva calls its substation automation offering for installations found in settings as disparate as utilities, generation and industrial plants and infrastructures. The design and marketing philosophy is to provide the 'technology framework to constantly improve the substation standardisation level while keeping a high degree of flexibility finally aiming at optimising the total asset cost of ownership' – ie scalability and function integration driving cost reductions.
The capabilities and features of this new version include a degree of standardisation that goes beyound the purely communication protocols, to include a standard library of automation schemes, and standard patterns from which to design projects. The degree of scalability is shown in the range of references, from a small RTU to a series of substations and in the system’s applicability to a wide range of sites from utilities to infrastructure projects. Its new communication features owe much to the existencxe of IEC 61850. which is more than simply a protocol – it implies the capability of creating fast distributed automation and introduces a degree of formal data naming.
Its capability, based on experience with more than 1000 systems installed around the world, includes, say Areva, full security of operation, a systemised approach that increases the power of the whole to more than the sum of individual components and a practical approach to retrofitting where minimising outages is the paramount factor.
It integrates protection, monitoring, automation and control into one coherent system intended to minimise the cost of ownership of substation automation. Its evolution has been made possible largely by the existence of IEC 61850, a new universal system of inconnection protocols that speeds up the system and reduces costs by the elimination of interfaces.
Early projects have demonstrated the scalability of the system, notably a series of standard protection and control bays in the Belgium transmission network, centralised architecture (RTU) in a German distribution substation, distributed architecture, possibly fully redundant, in new Egyptian and Mexican transmission substations, retrofit projects in a transmission substation in the UK, supervision of an overall industrial plant in Quatar, and others. Its primary purpose is to enable progressive investment that is secure for the future expansion needs of the plant.
Driven by standardisation
An accelerated rate of standardisation, the great change currently being undergone by substation automation technology, is generally regarded as a major advance in its evolution, comparable to the introduction of distributed control technology 15 years ago. It is being driven by the development UCA2/IEC 61850, a standard arrived at by international consensus that greatly simplifies the communication between devices. The heart of it is a standardised system of naming and services that speeds up communication, among different devices made by different manufacturers, to a highly significant degree. Earlier standardisation protocols such as DNP3 and its equivalent in IEC60870 were too limited to work fully with digital technology.
Standardisation also helps in fostering local engineering close to the end user when needed, by replicating project management and engineering processes, and benefitting from the standard bay packages developed at different kinds of sites around the world.
PACiS is intended to offer a unified architectural framework for building multiple solutions tailored to the needs of the application. It allows progressive upgrading of the system design in term of functions, size and performance. The system can be physically centralised (sometimes referred as RTU, substation server, PLC) or fully distributed with a variable level of redundancy of each component. It can be tailored to a single substation, as usually found within utilities, or to a scheme for the various substations, together with generation sources and perhaps load shedding, as encountered in industrial or infrastructure applications. It might initially be restricted to simply monitoring various signals – and then be extended to encompass distributed automation over a widely spread control network.
The system is built around a 100 Mbps Ethernet network with a ring or star topology, again, possibly redundant. Switch technology avoids any collision as previously encountered on Ethernet architecture, and provides virtual network (VLAN) for improved performance. UCA2/IEC 61850 devices from Areva or third party can be integrated on client, server or peer-to-peer mode.
Legacy communication protocols such as DNP3, IEC 60870-5-103/101 or MODBUS are also available to connect legacy devices. This is intended in particular for retrofit application where existing IEDs can be re-used, or for progressively migrating an entire substation automation system.
Other data sources
A key feature is the ability to work with information coming from various sources, such as physical devices delivering pure electrical information (eg a 50/60 Hz current transformer) or connected by serial communication links, especially when re-using devices already installed in the field. Alternatively, the source can be one or more operators carrying out maintenance, operation or management of the process or the system itself. PACiS can manage several types of data – positions, controls, measurements, disturbance records, setting, etc. Depending on the source and type of communication network this information may be allocated a quality tag such as time, validity, etc. Each item of qualified data is uniquely referenced in the system configuration tool in order to ensure full consistency of the information, as well as allowing it to be re-used in various parts of the system. Performance though would be highly dependent on the choice of the protocol, including speed (300 bps to 100 Mbps), services (master-slave vs. client-server) or communication objects.
Monitoring & analysis
PACiS' base function includes the monitoring of any data collected by the system, either locally or remotely. Extremely compact monitoring can be achieved on an embedded graphical LCD, displaying single line diagrams, alarms, measurements and sequence of event lists, usually a cost-effective solution for small substations. More sophisticated monitoring is carried out via one or more PC screens, providing useful features such as busbar colouring for easier maintenance, advanced alarm screens and accurate fault localisation within the system. Other features include advanced reporting, dual language display, and disturbance record analysis.
Controls are initiated by the operator, locally or remotely, and multiple checks are performed before the issue of a control signal in order to make it fully secure. For instance, a check can be performed to determine whether a single control is effective at a time on the whole system or on a single device. Another example is the use of interlocks, which are arrived at by logic equations or are the result of a dynamic topological analysis coupled with expert rules. Interlocks are managed as close to the process as possible in order to give the best security of operation. Interlocking conditions are graphically displayed on the operator's screen in order to immediately identify the locking conditions (if any) and make the appropriate changes before issuing the order. Each manual control is part of a "select before operate" sequence, where several options can be chosen. This includes the use of a synchro-check (in coupling or closing mode), and the bypass of syncho-check or interlock conditions where a valid user's authorisation is given.
Distributed automation among different devices, whether in the same substation or at different sites, is likely to become one of the key changes in the future. New arbitrages between costs and dependability can be achieved through the use of fast Ethernet communication protocols (UCA2/1EC61850), which replace traditional wiring with no extra hardware and can carry more detailed data. Used as an automation platform it can provide standard design using a comprehensive IEC 61131-3 editor accessing most of the system data, event driven processing with inherent robustness for avalanche conditions, and fast (100 Mbps Ethernet) peer-to-peer communication between physical devices. There are also in-built libraries of automation modules including protections, feeder automatic recloser and voltage regulation of parallel transformers.
System configuration definition is an essential tool for the initial database design and also for the evolution of the system throughout its lifetime. Its purpose is to provide a consistent set of information references distributed within the various components of the system.
The system configuration editor (SCE) provides an extremely efficient way to create a database, owing mainly to its object-oriented approach. The use of polymorph libraries, combining electrical data, automation sequences and graphical representation, makes possible the simplification and strengthening of a design solution.
Importing or exporting XML files can further enhance data consistency with engineering tools from other systems or devices. Use of the UCA2/IEC 61850 standards naturally leads to the use of hierarchical and process-oriented data references. This is a key criterion for overall engineering cost reduction and interoperability. The SCE, says its maker, includes advanced utilities of this type allowing for example simple comparison between database versions, filtering of expert data for non-specialists, and a topological editor.
A typical PACiS solution is likely to integrate several intelligent electronic devices (IEDs), such as protection devices, measurement centres, bay controllers etc communicating with the rest of the system by one or more protocols. PACiS is compatible with Areva’s Micom range of substation computers, typically RTUs, bay controllers and protocol converters. Non-Areva IEDs have also been added to the family of compatible devices.
Seeing the future
Master-slave communication is the ‘legacy’ technology. It is generally based on slow speed lines, linking a substation with a remote control centre or a protection reiay with a substation computer. State-of-the-art communication technology however is based on client-server and peer-to-peer links. It relies on fast Ethernet networks and offers new perspectives in terms of distributed functions, performance and flexibility. Coupled with adequate engineering tools systems such as PACiS are capable of increasing substation standardisation levels, managing innovative automation schemes within or between substations and overseeing efficient data exchanges with other substation management systems.