Inderscience Publishers

Considering line status in the dispatch process to minimise transmission congestion cost and maximise system usage

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In competitive electricity markets, energy locational marginal prices (LMPs) are commonly used to allocate energy payments and transmission congestion charges and credits. In these markets, energy prices and transmission pricing are highly affected by transmission constraints, where a congested transmission is accompanied by congestion costs, lower system utilisation, and higher energy prices due to resorting to out-of-merit order as expensive generating units are dispatched to alleviate congestion. In this paper we propose to use planned line switching to minimise transmission congestion cost and increase system utilisation. Statuses of lines are treated as {0,1} integers and integrated with the traditional social welfare problem, where the proposed dispatch problem is expressed as a mixed-integer nonlinear programming (MINLP) problem. The model used for energy market in the paper involves both spot (pool) transactions and firm bilateral contracts. To compare different dispatch options, the paper presents some performance indices. The presented method is applied to a three-bus and an eight-bus test systems, where the results show that considering opening of some transmission lines may improve outcome of social-welfare problem, as reflected in reducing total congestion cost and improving system utilisation. The method uses a dc load flow model, which can be extended for a full ac load flow model.

Keywords: energy markets, locational marginal prices, restructuring, social welfare, line status, transmission congestion costs, system usage, electricity markets, planned line switching, load flow modelling

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