Loss reduction by network switching
TL;DR: In this article, a linear programming (LP) problem formulation is used to model the switching operation in a power transmission network, where the objective function is expressed by the injected currents, taking into account that all nodes are constrained by constant active powers except for the slack node.
Abstract: Systematic and fast switching for the purposes of reducing losses in power transmission networks is treated as an optimization problem whereby switching is to be understood in a general and comprehensive way. Injected currents applied to a base network are used to model the switching operation. These currents are used as variables in a linear programming (LP) problem formulation. The objective function, i.e. the change in losses, can be expressed by the injected currents, taking into account that all nodes are constrained by constant active powers except for the slack node. The change of power of the slack node is the change in losses, which is obtained by a two-step approximation. Each single optimal switching operation is obtained by an LP-like operation followed by a load-flow update. The interaction between LP and AC load-flow leads to a sequence of optimal switching operations whereby losses are reduced to a minimum subject to the given constraints. >
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TL;DR: In this paper, the main challenges to the security constrained optimal power flow (SCOPF) computations are discussed, focusing mainly on: approaches to reduce the size of the problem by either efficiently identifying the binding contingencies and including only these contingencies in the SCOPF or by using approximate models for the post-contingency states, and the handling of discrete variables.
393 citations
TL;DR: In this paper, the authors analyze the N-1 reliable dc optimal dispatch with transmission switching and demonstrate that these networks can be operated to satisfy N 1 standards while cutting costs by incorporating transmission switching into the dispatch.
Abstract: In this paper, we analyze the N-1 reliable dc optimal dispatch with transmission switching The model is a mixed integer program (MIP) with binary variables representing the state of the transmission element (line or transformer) and the model can be used for planning and/or operations We then attempt to find solutions to this problem using the IEEE 118-bus and the RTS 96 system test cases The IEEE 118-bus test case is analyzed at varying load levels Using simple heuristics, we demonstrate that these networks can be operated to satisfy N-1 standards while cutting costs by incorporating transmission switching into the dispatch In some cases, the percent savings from transmission switching was higher with an N-1 DCOPF formulation than with a DCOPF formulation
377 citations
Cites background or methods from "Loss reduction by network switching..."
...It is also possible to have the losses decrease (see [6]), which is yet another possible benefit of transmission switching....
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...Transmission switching provides flexibility to the grid and may be used as a control method for problems including voltage stability, line overloading [3], [4], loss or cost reduction [5], [6], system security [7], or a combination of these [8]–[10]....
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TL;DR: This paper presents a co-optimization formulation of the generation unit commitment and transmission switching problem while ensuring N-1 reliability, and shows that the optimal topology of the network can vary from hour to hour.
Abstract: Currently, there is a national push for a smarter electric grid, one that is more controllable and flexible. The full control of transmission assets are not currently built into electric network optimization models. Optimal transmission switching is a straightforward way to leverage grid controllability: to make better use of the existing system and meet growing demand with existing infrastructure. Previous papers have shown that optimizing the network topology improves the dispatch of electrical networks. Such optimal topology dispatch can be categorized as a smart grid application where there is a co-optimization of both generators and transmission topology. In this paper we present a co-optimization formulation of the generation unit commitment and transmission switching problem while ensuring N-1 reliability. We show that the optimal topology of the network can vary from hour to hour. We also show that optimizing the topology can change the optimal unit commitment schedule. This problem is large and computationally complex even for medium sized systems. We present decomposition and computational approaches to solving this problem. Results are presented for the IEEE RTS 96 test case.
371 citations
Cites background from "Loss reduction by network switching..."
...If this were a lossy model, losses may increase or decrease, see [9], as a result of transmission switching....
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...Transmission switching has been explored as a control method for problems such as over or under voltage situations, line overloading [5]-[7], loss and/or cost reduction [8] [9], system security [10], or a combination of these [11]-[13]....
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25 Jul 2010
TL;DR: In this paper, the authors analyze the N-1 reliable DC optimal dispatch with transmission switching and demonstrate that these networks can be operated to satisfy N 1 standards while cutting costs by incorporating transmission switching into the dispatch.
Abstract: In this paper, we analyze the N-1 reliable DC optimal dispatch with transmission switching. The model is a mixed integer program (MIP) with binary variables representing the state of the transmission element (line or transformer) and the model can be used for planning and/or operations. We then attempt to find solutions to this problem using the IEEE 118-bus and the RTS 96 system test cases. The IEEE 118-bus test case is analyzed at varying load levels. Using simple heuristics, we demonstrate that these networks can be operated to satisfy N-1 standards while cutting costs by incorporating transmission switching into the dispatch. In some cases, the percent savings from transmission switching was higher with an N-1 DCOPF formulation than with a DCOPF formulation.
252 citations
Cites background or methods from "Loss reduction by network switching..."
...It is also possible to have the losses decrease (see [6]), which is yet another possible benefit of transmission switching....
[...]
...Transmission switching provides flexibility to the grid and may be used as a control method for problems including voltage stability, line overloading [3], [4], loss or cost reduction [5], [6], system security [7], or a combination of these [8]–[10]....
[...]
Book•
08 Oct 2008
TL;DR: Stochastic Security Analysis of Electrical Power Systems and Power System Transient Stability Analysis and Small-Signal Stability Analysis of Power Systems.
Abstract: Mathematical Model and Solution of Electric Network.- Load Flow Analysis.- Stochastic Security Analysis of Electrical Power Systems.- Power Flow Analysis in Market Environment.- HVDC and FACTS.- Mathematical Model of Synchronous Generator and Load.- Power System Transient Stability Analysis.- Small-Signal Stability Analysis of Power Systems.
248 citations
Cites background from "Loss reduction by network switching..."
...A fast relief of congestion may be possible by removing congested lines to prevent severe damages to system [84]....
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References
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TL;DR: In this paper, a current injection scheme is used to simulate the change in topology of a base network. But the injected currents are applied to the terminals of the elements of a socalled base network corresponding to those actually switched.
Abstract: Strategic switching can be achieved by a current injection scheme which simulates the change in topology. The injected currents are applied to the terminals of the elements of a socalled base network corresponding to those actually switched. This requires that the base network must contain all elements in the "in" state. The injected currents to be used as a compensation in the commonly employed system matrices (Y, Z) for the real change in topology can be taken as control variables in an optimization procedure for the switching problem. With the aid of a method similar to linear programming (LP) objective functions such as line current, short circuit current or even losses can be formulated. By means of a switching sequence consisting of elementary switching operations the desired objective function will be brought to its optimum value.
151 citations
TL;DR: In this article, a synthesis of methods is presented which combines security analysis and optimal power flow in order to achieve n-1 security, where the concepts of corrective switching are used to model outages.
Abstract: A synthesis of methods is presented which combines security analysis and optimal power flow in order to achieve n-1 security. The concepts of corrective switching are used to model outages, making it possible to generate constraints to be attached to the optimal power flow. A distinction is made between the secure state (conservative) and a state which is achieved by postcontingency rescheduling. Results for an 80-node system show the dispatch of control variables for the source states, the losses and the CPU-times. >
119 citations
TL;DR: In this paper, the authors developed a new formulation of distribution factors which is suitable for the analysis of the reactive power problem, which is based on the S-E (complex power - complex bus voltage) representation of a power network instead of the usual I-E(complex current-complex bus voltage).
Abstract: During recent years, problems associated with reactive power flow and bus voltages have acquired greater importance. The transmission capacity may sometimes be limited by reactive power considerations. In a few instances collapse of transmission network has been attributed to abnormal reactive power flow patterns. Some recent papers have addressed the question of improving the contingency study techniques for the reactive power flow problem. A commonly used method for contingency analysis is based upon the use of distribution factors. The distribution factor method of contingency analysis is very fast in its execution time, and for this reason is widely used in real time applications as well as planning studies. This technique is known to be particularly suited to the study of real power redistribution following an outage. It is not as accurate in dealing with problems of reactive power flow redistribution and accompanying effects on bus voltages. The inaccuracies are particularly significant when voltage controlled buses are present in the power system. The distribution factors are based on approximating active power injections by current injections under the assumption that voltage magnitudes throughout the system are kept constant. This is an unacceptable assumption for reactive power. This paper develops a new formulation of distribution factors which is suitable for the analysis of the reactive power problem. The new formulation is based on the S-E (complex power - complex bus voltage) representation of a power network instead of the usual I-E (complex current - complex bus voltage) formulation.
53 citations
TL;DR: A method is described for finding a better network configuration within a short time, despite the huge number of switching variants in real networks, based on a specific reduction of the variants and on the speedy analysis of variants.
28 citations