Emily Bartholomew Fisher

Optimal Transmission Switching

In this paper, we formulate the problem of finding an optimal generation dispatch and transmission topology to meet a specific inflexible load as a mixed integer program. Our model is a mixed-integer linear program because it employs binary variables to represent the state of the equipment and linear relationships to describe the physical system. We find that on the standard 118-bus IEEE test case a savings of 25% in system dispatch cost can be achieved.

Co-Optimization of Generation Unit Commitment and Transmission Switching With N-1 Reliability

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.

Optimal Transmission Switching With Contingency Analysis

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.

Optimal Transmission Switching—Sensitivity Analysis and Extensions

In this paper, we continue to analyze optimal dispatch of generation and transmission topology to meet load as a mixed integer program (MIP) with binary variables representing the state of the transmission element (line or transformer). Previous research showed a 25% savings by dispatching the IEEE 118-bus test case. This paper is an extension of that work. It presents how changing the topology affects nodal prices, load payment, generation revenues, cost, and rents, congestion rents, and flowgate prices. Results indicate that changing the topology to cut costs typically results in lower load payments and higher generation rents for this network. Computational issues are also discussed.

Smart Flexible Just-in-Time Transmission and Flowgate Bidding

There is currently a national push to create a smarter grid. Currently, the full control of transmission assets is not built in network optimization models. With more sophisticated modeling of transmission assets, it is possible to better utilize the current infrastructure to improve the social welfare. Co-optimizing the generation with the network topology has been shown to reduce the total dispatch cost. In this paper, we propose the concept of just-in-time transmission. This concept is predicated on the fact that transmission that is a detriment to network efficiency can be kept offline when not needed and, with the proper smart grid/advanced technology, can be switched back into service once there is a disturbance. We determine which lines to have offline based on the optimal transmission switching model previously proposed. A secondary topic of this paper focuses on flowgate bidding. Approved by the Federal Energy Regulatory Commission and implemented within the SPP and NYISO networks, flowgate bidding is defined as allowing a lines flow to exceed its rated capacity for a short period of time for a set penalty, i.e., price. We demonstrate the effectiveness of these models by testing them on large-scale ISO network models.

Understanding Bulk Power Reliability: The Importance of Good Data and a Critical Review of Existing Sources

Bulk power system reliability is of critical importance to the electricity sector. Complete and accurate information on events affecting the bulk power system is essential for assessing trends and efforts to maintain or improve reliability. Yet, current sources of this information were not designed with these uses in mind. They were designed, instead, to support real-time emergency notification to industry and government first-responders. This paper reviews information currently collected by both industry and government sources for this purpose and assesses factors that might affect their usefulness in supporting the academic literature that has relied upon them to draw conclusions about the reliability of the US electric power system.

Co-optimization of generation unit commitment and transmission switching with N-1 reliability

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.

A nodal pricing analysis of the future German electricity market

The electricity market in Germany is likely to undergo several significant structural changes over the years to come. Here one may think of Germanys ambitious renewable agenda, the disputed decommissioning of nuclear facilities, but also unbundling of TSOs as enforced by European regulation. This study is a scenario-based analysis of the impact of different realizations of known investment plans for transmission and generation capacity on the future German power market while accounting for internal congestion. For this analysis the static equilibrium model of the European electricity market COMPETES is deployed, including a 10-node representation of the German high-voltage grid. Results for the multi-node analysis indicate that price divergence and congestion are likely to arise in the German market as renewable additions affecting mainly the North of Germany, the debated decommissioning of nuclear facilities in the South, and the expected decommissioning of coal-fired facilities in Western Germany appear to render current investment plans for transmission capacity insufficient. The current system of single-zone pricing for the German market may therewith be compromised. However, transmission additions would not benefit all market parties, with producers in exporting regions and consumers in importing regions being the main beneficiaries. Vertical unbundling of German power companies could increase the incentive for constructing transmission lines if generation capacity would cause Germany to be a net-importing country. In case Germany remains a net-exporting country, the effects of vertical unbundling on cross-border capacity are less clearcut.

Optimal transmission switching with contingency analysis

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.

Spot markets for reactive power

There is concern that the present structure of reactive power compensation in competitive power markets may not encourage efficient or adequate investment in or operation of reactive power assets. New ways must be explored to promote appropriate investment and operation of reactive power capability in a way that bolsters system security as well as economic trade. In this paper I argue that spot markets for reactive power, in conjunction with forward markets, are an important component of a successful strategy to achieve this by (1) improving real-time efficiency, (2) facilitating open access to transmission, and (3) supporting long-term contracts. I also propose a particular spot market design and characteristics of the resulting nodal settlement. Because transmission assets can produce and consume reactive power, in some cases to a high degree and with fine controllability, they are involved as active participants in this proposed spot market, and both the capacity and electrical characteristics are valued.