A Petri Net model for electrical power systems operating procedures

The operation and the maintenance of electric power systems are governed by a set of procedures required to ensure that any intervention on the system will be performed under safe conditions, considering the inherent dangers coming from the presence of live conductors, parts and components. Although the main safety-related concepts like energy isolation, earthing, interlocking and lockout-tagout are consolidated in electric power system practice, their translation in the procedures preparation process requires a deep analysis of electric network operation and maintenance requirements, components properties and topological characteristics. A formalization of the general rules and methods adopted in the preparation, control and actuation of electrical procedures has been proposed utilizing a Petri Net (PN) model representing the system and its state changes in graphical and analytical form. This allows us to better understand the logic behind a procedure and to allow an immediate consistency check of the correctness of the procedures' operating sequences. The suggested methodology supports the design process and the preparation of working procedures covering a wide range of activities. This also gives assistance to the designer and to the operator through simple rules and a graphical aid. In addition it is useful for those non-automatic processes (electrical, mechanical, etc.) to allow an auto check of the Lockout-Tagout (LOTO) procedures. Using the concept of effects superposition, the method is applicable to larger systems having a complex topology. It can be proven that a designer can build large Petri net models starting with several basic modules, each of which describes an equipment function. A result of this process is that the designers better understand, the main concepts. These concepts include; concurrency, synchronization, mutual exclusion and sequential relations involved in the system control coming from the graphical representations of Petri nets. Another aspect is the possibility of carrying out an operational system performance analysis under different settings, getting useful results in the process of selecting the optimal configuration and the preparation of the correct procedure. Finally, the model can be used as an aid for automatic generation of real-time control programs using a Petri net-based simulation.