Lisp at IATOS


Intelligent Aid To the Operator in an electrical Substation

IATOS is a knowledge based system designed to facilitate the execution of complex operations in an electrical substation. IATOS is an "intelligent" module, integrated in a classical digital control system.

IATOS is able to :

  • plan sequences of operations which lead the system to the target configuration while satisfying operational constraints ;
  • assist the operator in the execution of this sequence ;
  • adaptively react and re-plan in case of incidents or abnormal events.

Target users

IATOS is intended for supporting operators who are not particularly familiar with the substation to be operated.
It could also be used as a training tool for operators, generating operations or checking the operator actions and giving advice.

IATOS is in operation at the Angleur substation : a 80 MW-substation which supplies the city of Liège (Belgium).

How does it work ?

IATOS is a knowledge based system with a knowledge base, an interference engine and a user-interface.

The knowledge base is composed of two parts :

  • The factual knowledge, which consists of the (static) topological description of the substation, the (dynamic) switching states, the definition of standard target configurations, the list of constraints to be checked, etc. The facts are described in terms of graph theory (nodes, branches, branch costs, ...).
  • The procedural knowledge, which is made of several classes :
    • the rules detecting violations of constraints (interlocking constraints, functional constraints and constraints resulting from practice) ;
    • the rules giving basic switching sequences according to the initial state and the target configuration ;
    • the rules generating auxiliary switching sequences to avoid violations for each type of constraint.

The inference engine mainly consists of a recursive mechanism which gradually builds a complete, valid and optimal sequence, using the facts and the rules of the knowledge base.

IATOS is able to manage several types of constraints :

  • hard permanent constraints (constraints applicable to all states i.e. the temporary states during the execution of an operation and the final state) ;
  • hard stable constraints (constraints applicable to stable states, i.e. states at the end of an operation) ;
  • action constraints ;
  • soft stable constraints (constraints generally related to good practice rules specific to the substation and to the utility ; these constraints need not be absolutery respected) ;
  • functional constraints related to an operation : these constraints express the aim of an operation.

In order to avoid information duplication and to unify the man-machine-interface, IATOS is designed as a supplementary software tool to a classical digital control system which deals with data acquisition, control and other basic SCADA functions.

Main functions

The system covers all "realistic" operations (putting into service or out of service of bays, by-passing bays, changing busbar, clearing and restoration of a part or the whole substation, etc.) starting from normal and abnormal substation states. It is able to cope with most possible incidents during operation (circuit breaker tripping, blocked switch, etc.).

For the user, the advantages of operating with such a system are :

  • user friendliness allowing the intervention of occasional operators in the substation ;
  • automatisation of the working method ;
  • reduced risk of faulty operations ;
  • assistance in incidental situations.

Competitive advantages

Unlike predefined switching sequences presently available in digital control systems, IATOS generates switching sequences consistent with any initial substation state. Moreover, if an incident occurs during the sequence execution, IATOS assists the operator by re-planning the sequence to address the new situation.

Another advantage of IATOS is that it globally views the operation and uses a complete topological set of interlocking rules. IATOS is able to distinguish temporary states from stable states and apply different sets of constraints to each state category. Moreover, this global view of the operation allows the system to be aware of the objective of the operation, making it possible to implement fontional constraints. These kinds of functionnalities are not offered by classical digital control systems.

Finally, IATOS could also be used as a training tool.

Hardware and Software environment

IATOS runs on a dedicated computer. It jointly uses the control system database for access to static and dynamic data, and the control system interlocking module to check the generated switching sequences. IATOS interacts with the user through the control system peripheral devices (display and track-ball).

IATOS has been developed in LISP + CLOS, making extensive use of the object-oriented programming facilities.

The software runs under WINDOWS on a 32 MB RAM - Pentium based PC.

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Last update : 22/12/2000