An Algorithm for Finding Minimal Load Interruption Costs

University essay from KTH/Elektriska energisystem

Author: Jan Lavenius; [2012]

Keywords: ;

Abstract: This thesis presents an algorithm for finding the minimal interruptioncost associated with the loads.Electric power systems are necessary to transfer electric energy fromproducers to consumers. The power system may lose stability as thesenonlinear systems are subject to contingencies. The loss of stabilitymay result in large costs for the society, by the loss of productivityand worsening standard of living. If the likelihood of instability is low,then it may be that it is not economically motivated to allocate costlyresources necessary to prevent this from happening. For some casesload shedding is the alternative with best economical performance, torestore the stability and ensure that delivery of power is not interrupted.With increasing amounts of renewables in a power system, the planningand scheduling of the electric power production will get more difficultto forecast and control. Therefore the system operators will needto be able to handle more diverse situations than before. Thus thereis a need to find computationally efficient methods to predict systemstability and the minimal load shedding needed.This report uses second-order approximations to the stability boundariesof the system, developed and calculated by Magnus Perninge andCamille Hamon to determine how much and where the load sheddingshould be done to shed the minimal amount of load that restores thestability of the system.Two cases, the IEEE 9-bus system and the IEEE 39-bus system,illustrates the proposed method and compares three different methodsused to determine the load shedding. The results show that the approximationscan be used to minimize the load shedding, and that theamount of load shed is significantly reduced. Time-domain simulationsof the system were necessary to ensure the stability of the system anddetermine of much margin that is needed to the approximations.The methods and approximations used in this report could in thefuture be applied to real power systems, a possible application is tocalculate the severity of contingencies and use the information to minimizethe total costs of the system when considering operation andinvestments. Another possible application is to design automatic loadshedding controllers using wide-area monitoring to increase the systemreliability.

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