For the start of the Millennium, Electricité de France (EDF) plans to have in place a completely overhauled national control centre (NCC) to guarantee the safe operation of France’s national grid and reduce generation and transmission costs.

EDF has therefore embarked on a massive development programme. The cornerstone of the initiative is the new NCC, ‘Système National de Conduite’ (SNC). This system will replace the existing control centre, SYSDIC, which has been in service since the early 1980s. The IT hardware which SYSDIC runs on is obsolete, and is unable to manage all 400 and 225 kV substations as well as the improvements in IT functionality required.

EDF’s new telecontrol network, currently being developed, will enable data exchanges between the NCC, regional control centres, power stations and EHV substations.

EDF has drawn up a progressive development strategy for the NCC, which falls into two main stages.

The priority of stage one, or SNC V1, is to increase the existing system’s capacity. Additional data collected from the thermal and hydroelectric plants will significantly improve real-time monitoring of the grid and its operating margins. It will also cater for the key national 225 kV substations.

EDF will also use this stage to integrate innovative functionality into the system and will result in more secure monitoring of the bulk power system thanks to a higher level of security analysis. These functions have already been trialled at the existing SYSDIC system in prototype form.

During the second stage, further new functionality will be added to the system, particularly in the area of security forecasting to within a few hours, ensuring that the system is more cost-effective. This will give the NCC operator access to powerful decision-making tools, providing improved real-time and short-term knowledge about the state of the bulk power system, so that corrective action can be taken to manage the balance between supply and demand, or adjustments can be made over the course of the day to units scheduling. Innovative functions in the system will be enhanced, for example, to enable real-time analysis of corrective actions or automatic investigation of topological solutions.

Importantly, the innovative functions will improve real-time analysis of the bulk power system:

  • An estimated status report will be issued every five minutes, giving a comprehensive picture of the current state as calculated from the available remotely monitored substations.

  • Subsequently, every quarter of an hour or on demand, a security analysis report simulates a list of trippings and examines the potential consequences. A wide variety of trippings can be simulated, ranging from the single to multiple lines or units trip and busbar tripping. Advanced man-machine interface enables the operator to visualize the results of these analyses.

    In addition, short-term security analysis functions have been added, enabling the operator to gradually build up corrective actions in response to trippings using any of the numerous interactive functions at his disposal. For example, by modifying the current situation of the network under consideration, the position of circuit breakers, the power of particular units, the consumption or exchanges with neighbouring countries can be changed. Analysis of these actions also feeds into the real-time security analysis for the system.

    Powerful solutions<

    The new NCC will process four times the current amount of data, enabling the control and monitoring of:

  • two hundred 400 kV substations and eight hundred and fifty 225 kV substations

  • almost five hundred 400 kV lines and one thousand six hundred 225 kV lines

  • 120 units connected to the 400 kV and 315 units to the 225 kV networks

    To achieve this, the system must be capable of receiving some 16 000 ATM and DTM every 10 s, with a total capacity of up to 55 000 SS and DS.

    To minimize risk and maintain timescales for the project, EDF decided to rely as far as possible on off-the shelf solutions, while also capitalizing on its in-house expertise in EMS.

    In the first stage of the project, a supplier is responsible for designing the system’s global architecture and developing the data acquisition, monitoring, supervision and displays functions. EDF itself is then responsible for the development of the EMS functions, to be integrated on the supplier’s platform via programming interfaces.

    In May 1996 EDF invited tenders for two contracts: a turnkey contract for specifying, developing, installing and implementing SNC V1, and a maintenance and upgrading contract for the system.

    The first contract covers the design of a global architecture for the system, capable of evolving to meet the functional targets set for the end of the second stage of the SNC’s development. It also includes the provision of equipment and the associated base software for four systems: the two independent CC systems (the on line/hot standby system and its emergency back-up system); the off-line database system; and the DB test system.

    The first contract also includes the development of the SCADA functions that will allow the existing system to be upgraded, and the development of programming interfaces which ensure that the system is able to cope with the implementation of the functions being developed by EDF. The supplier is also responsible for setting up the databases, as well as for providing engineering specifications giving EDF the appropriate guarantees in terms of the performance, reliability, management, quality and system security.

    In August 1997, EDF signed a contract with Sema Group for SNC V1. A partial in-service implementation – enabling the new EMS functions currently being tested to be made available to the national operator – is due for August 1999. This represents a key step in the progress of the project. The completed first version (SNC V1) will follow in August 2000. The second contract for maintenance and upgrading will be concluded before the end of the SNC V1 development contract.

    Modular design

    The SNC V1 development is based on Sema Group’s monitoring and control system, ADACS (Advanced Data processing And Control System), the result of experience gained in the development of more than 200 control systems currently in service or being installed.

    ADACS’ modular design and organizational flexibility enables use of the hardware and software architecture best suited to the customer’s requirements.

    ADACS consists of a basic set of distributed modules – each carrying out a well-defined function – and a software bus for communication between modules. This architecture ensures that existing functions are well separated and allows new functions to be easily added. It also simplifies portability and makes it easy to develop an architecture which matches the performance and capacity requirements of each application in terms of processing speed, number of input and outputs, number of variables, and so on.

    This modular architecture means that ADACS can be used to control large systems or small networks. A basic implementation can be limited to a single workstation running only those modules necessary for the required processing to be carried out. These modules will still communicate via the software bus, so that the application can be distributed to run on a larger number of machines at a later date. ADACS is a generic solution, capable of evolving with new requirements.


    Data organization in ADACS is based on the ‘object-type’ model. This gives a clear structure, and is well-suited to modelling entities in physical processes such as sensors, actuators and other hardware devices. The operator has a clear and well-controlled representation which can easily adapt to mirror changes in processes.

    The characteristics of the object-oriented approach also result in more efficient application development, as well as improvements both in the operation and further development of the system throughout its lifetime.

    This object-oriented approach has several advantages:

  • During the specification and design phases, both the client and the supplier can use the same simple language.

  • During development, data and process structuring and the use of object libraries saves development time.

  • In the implementation phase, data validity checked on one representation ensures its validity for all other representations. In addition, checking that an object is being correctly processed automatically covers all objects of the same type.

  • During the maintenance phase, a single modification in an object type is automatically reflected in all objects of the same type.

    For applications that require a high level of availability, the architectural elements are implemented in synchronized redundancy. Parallel operation of the two real-time processors means that if the master breaks down, the switch can be made immediately to the back-up machine without losing data or messages, or any operational down-time. This function – an integral part of ADACS – is transparent to the application itself, which carries out its tasks in complete continuity in the case of failure. A high throughput FDDI link is used for the synchronized operation of both processes.

    A subset of the real-time database is distributed on every workstation or server which needs it. Essential data and images are stored locally at each workstation and processing server, as it is not necessary to transfer them on the network on call. All the real-time variables required for display are available permanently in memory at each operator workstation. This allows information to be displayed and updated immediately.

    The local area network provides a reliable distribution protocol that supports high performance communications by avoiding network overload. This protocol can distribute one message to several machines instead of sending each target workstation or server a separate message.

    ADACS includes client/server technology which supports connections to other systems and enables off-the-shelf software packages to be connected to ADACS.

    A communication layer which uses the distributed computing environment (DCE) standard, linked to application programming interfaces (APIs), enables the development of distributed user applications. These APIs enable external applications to access real-time and archived data for read/write operations, synchronization and so on.

    The real-time server is connected to the ADACS software bus and incorporates a real-time process database. The archiving server, which is also connected to the ADACS software bus, is an extension of the ADACS archiving module.

    Taking advantage of this combination of features enabled Sema Group to create a highly competitive solution, well-suited to EDF’s requirements, particularly in terms of upward compatibility, standard functionality, the specific requirements of the SNC system and openness of the overall system.

    Standard functionality

    ADACS offers all the standard functions of a SCADA system, including network modelling – offering state-of-the-art graphical displays representing dynamic changes in network topology –and management of different alarm types. Load frequency control ensures the automatic regulation of units, sending a value corresponding to the increase or decrease required for frequency and exchanges control.

    ADACS also includes leading-edge techniques such as multiple re-sizeable windows with a ‘copy/paste’ option for transferring data from one function to another. DCE communication – an OSF standard – ensures a basic level of security for all client/server exchanges. The solution also utilises TCP-IP network management protocols.

    As with any renewal project, SNC V1 has to encompass a certain number of existing processes linked to the network’s current operational approach and equipment. In some cases, this involves adding processing functions not included in standard ADACS functionality.

    ADACS processes are encapsulated in independent modules which can be called from specific object types. In addition, new processing modules to meet particular requirements can be easily added without altering the ADACS structure in any way.

    ADACS’ open design facilitates communication with external applications and at various levels. The solution communicates with distributed systems via DCE. This open approach has enabled the construction of an information server, using FTP (File Transfer Protocol), giving the SNC access to EDF’s information systems.

    The success of such a major project obviously depends not only on the choice of a solution that meets these exacting technical requirements, but also on how the development contract is managed. The project organization established by Sema Group is designed to guarantee the requisite quality assurance and security standards at every level of the project and during each phase of its development.

    To ensure that the maintenance contract can continue to meet EDF’s requirements for upwards compatibility in SNC V1 in the most appropriate way, special emphasis has been placed on factors such as documentation, traceability, quality and security indicators, metrics, and the coverage of test programmes.

    Sema Group is highly experienced in the management of large-scale technical information projects. As well as electricity power system, ADACS is used in the control of many different industrial processes. The solution is at the heart of the command and control systems for the four 1475 MW nuclear units at Chooz and Civaux in France, as well as the two Ling Ao nuclear units being built by Framatome in China. In addition, ADACS is currently being used for water treatment, the centralized technical management of airport terminals, aluminium production, and a host of diverse applications worldwide.