Hierarchical time-extended petri nets as a generic tool for power system restoration

Founias, NA; Hatziargyriou, ND; Valavanis, KP

dc.contributor.author	Founias, NA	en
dc.contributor.author	Hatziargyriou, ND	en
dc.contributor.author	Valavanis, KP	en
dc.date.accessioned	2014-03-01T01:12:58Z
dc.date.available	2014-03-01T01:12:58Z
dc.date.issued	1997	en
dc.identifier.issn	0885-8950	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/12302
dc.subject	Hierarchical timeextended petri nets	en
dc.subject	Power system restoration	en
dc.subject	Restoration planning	en
dc.subject.classification	Engineering, Electrical & Electronic	en
dc.subject.other	CONCURRENT SWITCHING SEQUENCES	en
dc.subject.other	SIMULATION	en
dc.title	Hierarchical time-extended petri nets as a generic tool for power system restoration	en
heal.type	journalArticle	en
heal.identifier.primary	10.1109/59.589712	en
heal.identifier.secondary	http://dx.doi.org/10.1109/59.589712	en
heal.language	English	en
heal.publicationDate	1997	en
heal.abstract	The features of the Power System Restoration (PSR) problem, i.e. its combinatorial nature, the use of knowledge from a broad range of sources and of different types along with the number of criteria to satisfy, make it a very difficult decision making process. This paper aims at proposing an innovative approach to provide support to system planners and operators when a blackout occurs and enable a qualitative analysis of the feasibility of the restoration procedures followed. The approach employs an extension of the model-based Petri Nets theory -Hierarchical Time-Extended Petri Nets, H-EPNs, a valuable graphical and mathematical modeling tool applicable to many areas. As a graphical tool, PNs can be used as a visual-communication aid similar to flow charts, block diagrams, and networks with the additional ability to simulate the dynamic and concurrent activities of systems utilising tokens. As a mathematical tool, it is possible to set up state equations, algebraic equations, and other mathematical models governing the behaviour of systems. System Restoration itself is a hierarchical problem. It embodies an inherent 'time hierarchy' associated with the determination and execution of the restorative control actions in the various stages of system reestablishment. The hierarchical modeling approach used by H-EPNs facilitates the re-energization of the system and leads to restoration plans which are better structured and easier to modify, while a better decision-making process can be achieved. For the formulation of the restoration strategies, the hierarchical modeling utilizing H-EPNs follows three phases: 1. top-down decomposition of the system into a set of component nets, 2. component net modeling, and 3. bottom-up synthesis of the system H-EPN model. The top-down decomposition is accomplished by a functional breakdown of the overall restoration process that eventually leads to a set of well defined operations common in diverse restoration strategies. In the final stage, after the H-EPN subnet for each generic restoration action has been validated, the resulting overall H-EPN power system model can be constructed by using bottom-up synthesis techniques. Indicatively, the suggested H-EPN model for the energize line subnet is demonstrated in Figure 1. The token in place p1 indicates entry into the subnet. The problems of transient voltage, sustained overvolt-age and charging current that may appear during energization of long lightly loaded transmission lines are checked within the H-EPN model with the aid of the decision places, p3, p6 and p9. If an operating constraint is violated, the model will suggest a modification to the plan in the form of a ""corrective action"", depending on the actual status of the system. The proposed H-EPN framework has been applied to investigate the blackstart procedures following the 1989 blackout of the Hellenic power system. A synthesis of the primitive restoration actions (subnets) has been performed. The places and the corresponding transitions of the model illustrate the restoration actions of unit blackstart, bus energization, line energization, load pickup and unit crank that take place during island reintegration. This is achieved through a cascade connection of the predefined subnets. H-EPN based platform can be used as a planning restoration tool for studying various scenarios It can be implemented as a decision support system for the power system operator in order to: i) help him choose among various ways of initiating the restoration ii) propose several alternative courses of action for a given system condition, iii) assist him in selecting intermediate restoration objectives, iv) alert him when dan-gerous situations arise, v) explain how the system arrived at these alternatives with schematic visualization, vi) evaluate the feasibility of alternative restoration strategies based on analytical tabulated data from off-line studies in conjunction with H-EPN structural properties, vii) display the applicable - pre-defmed restoration procedures. At the present stage, the developed H-EPN model can be used for PSR planning, in an off-line, stand-alone mode. The encoded reasoning in the H-EPN model is based on logical interrelations represented by multiple classes of places and transitions. The issue of path finding is addressed with predefined paths assumed to be available during system rebuilt These switching sequences are based on established practices. Ongoing work concerns the development of an integrated software environment which will make use of the specialized Petri Net software and at the same time will be able to interchange data and results from system simulation programs In this way a more accurate checking of the feasibility of the restoration actions will be possible. At its ultimate stage, H-EPN modeling could be viewed as an interactive assistant to the operator, being part of a sophisticated decision-support environment. (Figure Presented) Figure 1. H-EPN model for the ""Energize line"" subnet.	en
heal.publisher	IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC	en
heal.journalName	IEEE Power Engineering Review	en
dc.identifier.doi	10.1109/59.589712	en
dc.identifier.isi	ISI:A1997WW13000058	en
dc.identifier.volume	17	en
dc.identifier.issue	5	en
dc.identifier.spage	71	en
dc.identifier.epage	843	en