Study Of Power System Transmission Congestion And Its Associated Problems

As restructuring and deregulation deepen in the power industry, open access is gaining greater attention. The competitive environment incorporating open access poses the greatest challenge to power system operation. Open access implies that the opportunities to use the transmission system must be equally available to all buyers and sellers. More and more transactions are utilizing the transmission system in a deregulated environment. However, the capacity of the system is limited by physical constraints and reliability requirements. The violation of any of the various constraints of the system (line flow limits/thermal limits, voltage profile limits, stability limits, et al) causes a situation which is called as congestion. Especially, in systems having weak connections among areas, congestion problem frequently occurs due to overloading or due to voltage security requirements. Congestion management deals with the relief of congested transmission networks in modem deregulated electricity markets.Congestion segregates electricity market and weakens competition mechanism, which causes invalidation of optimization of generating resources in the whole network. Congestion also increases generating costs, and thus makes market less efficient. Although there are a lot of literatures discussing congestion, many problems about congestion management are still not well solved. This dissertation studies those unsolved problems associated with congestion management and proposes some effective strategies to solve them. Those novel strategies proposed are as follows:(1) Research on the transmission congestion due to static voltage security constraints has vital meaning for guaranteeing smooth competition in power market and enhancing efficiency in electric power systems. This paper focuses on topics relating to this kind of congestion. The on load tap changer of the transformer and switched shunts can play an important role in guaranteeing static voltage security. Those two methods with generating units redispatching have been introduced in this dissertation for congestion management to eliminate static voltage security constraints.(2) Conception of load elasticity is introduced in detail, and model of OPF considering biding of elastic load in two-sided auction market structure is discussed. A simple example is used to explain elastic load's effect on social welfare, merchandise surplus, nodal price and congestion cost.(3) The Merchandise surplus is deduced in detail for congestion, and the apportion means of this surplus is proposed. The cost of power will be increased under transmission congestion, and the increased part of the cost is the congestion cost. To allocate the congestion cost fairly is beneficial for relieving the congestion. The Aumann-Shapley pricing and Shapely value is illustrated in detail.(4) The definition of market power is presented from the view of economics and regulation. Market power is evaluated form market composing and market behavior in this dissertation. Some measures for restricting the market power in electricity market are proposed. Bidding strategies, such as withholding capacity and bidding at higher price, are analyzed. The impact of transmission congestion on the loctional marginal price (LMP) is studied in detail. Congestion will cause relative scarcity of generating capacities in the congested areas, so generation companies in those areas have locational market power.(5) When the network is congested, the LMP consists of three components: the marginal cost of generation at the system, the marginal cost of losses and the congestion cost. And the LMPs at all other buses of the network can be expressed as a weighted average of the LMPs at the two buses of the congested line. Two decomposed methods are proposed to calculate the effect weights, which are DC flow calculation method and imagine generator method. The economic meaning of Lagrange multiplier is illustrated and the relation between this multiplier and congestion charge is explained.(6) Based on inelastic loads, the social effects of...