Flexible Network Topologies and The Smart Grid in Electric Power Systems

Open Access
Barrows, Clayton Paul
Graduate Program:
Energy and Mineral Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
November 30, 2012
Committee Members:
  • Seth Adam Blumsack, Dissertation Advisor
  • Reka Z Albert, Committee Member
  • Andrew Nathan Kleit, Committee Member
  • Luis Ayala, Committee Member
  • Paul Hines, Committee Member
  • Power System Analysis
  • Optimization
  • Electricity Markets
  • Complex Network Science
Recently, the demands placed on the electrical transmission system have increased disproportionally relative to the investments made in the system. As a result, the system has become increasingly constrained, hindering the ability of the transmission system to facilitate competition among generators. New transmission can fix this problem, but is difficult to construct due to political, environment and financial concerns. Topological reconfigurations of the transmission system could improve the efficiency of power system operations and represents a particularly valuable application of the smart grid. However, in practice the topology reconfiguration problem is difficult to solve. Reconfiguration of the transmission network can be accomplished through topology optimization. The act of temporarily removing transmission lines from service, known as “transmission switching”, can relieve transmission congestion and enable the re-dispatch of lower cost generators. Optimal Transmission Switching (OTS) co-optimizes the generator dispatch and the network topology and has been shown to minimize costs when applied to test systems. When considering every line in the network as switchable, the problem scales such that 2#-lines distinct network topologies must be considered. Real systems often contain tens of thousands of transmission lines. The size and complexity of OTS has limited optimal solutions to small test systems and linearized DC power flow models. A Marginal Analysis of OTS investigates the predictors of the probability with which each transmission line is optimally switched and the contribution of each line to cost savings. The analysis leads to two conclusions. First, the majority of cost savings can be achieved through switching a small subset of lines. And second, the effects of transmission switching are relatively localized. These conclusions lead to the development of two strategies to reduce the computational complexity of the OTS problem. Network partitioning methods are used to iv generate sub-networks where the OTS problem can be solved in parallel and then aggregated to form a complete system solution. Additionally, a candidate switchable line screen based on the Line Outage Distribution Factors is presented to identify a superset of switchable lines. Thus far in the evolution of transmission topology and generation dispatch co-optimization problems, optimal solutions have been obtained using a linearized de-coupled power flow model. While this model is useful for many approximations, it fails to describe reactive power flows and voltage magnitudes; two critical parameters when considering the feasibility of a generation dispatch. However, topology optimization presents an intractable problem when implemented in the nonlinear and non-convex AC power flow model. The discrepancies between the AC and linearized DC power flow models have created speculation that the cost savings generated by optimizing transmission topology in the DC network may not translate into cost savings in the AC network. Using a method developed to achieve feasible OTS solutions in both the AC and linearized DC power flow models, cost savings are achieved and enhanced in the topologically reconfigured AC power flow model.