RELIABILITY COST ASSESSMENT OF POWER TRANSMISSION NETWORKS IN THE ENVIRONMENT OF REREGULATED ELECTRICAL ENERGY MARKET

摘要

During the last two decades, there has been anincreased concern to justify economically the reliabilitylevel of power supply being provided by the powerutilities to their customers. In order to examine theeconomics of reliability in a power system, it isnecessary to estimate the reliability level and itsassociated costs and to determine the worth of powersupply to the customers with its associated financialvalue. Reliability worth can be expressed in terms of theexpected customer interruption cost. Electric powerutilities are also increasingly interested in spot pricingof electricity because of the intensified competition inenergy markets. The cost of providing electricity, ingeneral, varies with time, location, supply voltage,weather conditions and other system and customercharacteristics and the spot prices can achievesignificant gains in short-term efficiency.The components of spot pricing can be grouped intwo different categories known as marginal operatingcosts and marginal outage costs. The marginaloperating costs are generally defined as the fuel costsand line losses costs that are incurred in serving anincremental load demand as well as the maintenancecosts and the system security costs that can vary withusage. The marginal outage costs are defined as thecustomer outage costs related to both capacityshortages and network capacity constraints that areincurred in serving an incremental load demand. Both,system operating and customer interruption costsdepend on system states and on the type of customersbeing connected at each system load busbar.The objective of the paper is to describe an improvedand efficient computational methodology for evaluatingthe reliability worth of power transmission networksconsidering the time varying loads and the type ofcustomers being connected at each system load busbarand the various characteristics of interruptions thatwere discussed above. The developed methodology forthe evaluation of the marginal outage cost is based on aMonte - Carlo sequential simulation approach,considering the composite power generation andtransmission system. Additionally, a minimisation modelof the operating and interruption costs has beendeveloped applying the features of the linearprogramming method. The minimisation model is usedfor each hourly interval experiencing transmission lineoverloads and its intention is to alleviate them byrescheduling generation outputs to avoid loadcurtailment, if possible, or to minimise total loadcurtailment, if unavoidable. The basic features of thismethodology include the recognition of the appropriateinterruption costs for the different system busbars andthe consideration of the duration of systemcontingencies that may be occurred. The real designand operational features and practices applied in thereregulated electrical energy market are representedrealistically and efficiently. For this purpose, theappropriate simulation procedure takes into account theprinciples of a model that is under development in orderto be used in the reregulated electrical energy market inGreece. A set of appropriate reliability and cost indicesis calculated for each load-point of interest and theentire system under consideration. The developedcomputational methodology has been implementedefficiently into an interactive computer program thatwas written in FORTRAN. Various case studies wereconducted using the IEEE Reliability Test System. Thesestudies take into account the power interruption coststhat were estimated through a customer survey beingconducted recently in Greece.