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# Optimal Transmission Switching (OTS)

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The Optimal Transmission Switching deals with changing the transmission network topology by system operator in order to improve voltage profiles, increase transfer capacity and reducing the market power. The change in topology can be done by one or combination of the following actions:

• Deliberate outage of some specific transmission lines
• Adding phase shifters (these devices can change the angle difference between two connected buses)
• Adding  Flexible Alternating Current Transmission System (FACTS) devices (these devices can increase/decrease the impedance of two connected buses in the system)
• Adding reactive series impedance (these devices can increase the impedance of two connected buses in the system)

The idea of topology dispatch was first introduced in [1] and demonstrated how it can provide the electricity market with greater efficiency and competition. They were using deliberate outage of lines in the system.
This idea was further developed in [2] by not only considering the normal operation but also the n-1 contingencies. They added the variable topology into security constrained OPF. In [3], the impact of transmission switching on financial transmission rights (FTR) has been investigated. The unit commitment problem constrained by transmission system is solved in [4]. The application of FACTS devices in transmission topology dispatch has been investigated in [5]. The proposed algorithm is LP and can be applied to large scale transmission systems.

[1] R. P. O'Neill, R. Baldick, U. Helman, M. H. Rothkopf and W. Stewart, "Dispatchable transmission in RTO markets," in IEEE Transactions on Power Systems, vol. 20, no. 1, pp. 171-179, Feb. 2005.
[2] N-1 DCOPF formulation: Hedman, Kory W., et al. "Optimal transmission switching with contingency analysis." Power Systems, IEEE Transactions on 24.3 (2009): 1577-1586.

Optimization Methods

MIP:
[3] W. Hedman, S. S. Oren, and R. P. O’Neill, “Optimal transmission switching: economic efficiency and market implications,” Journal of Regulatory Economics, vol. 40, no. 2, pp. 111-140, Oct. 2011.
[4] W. Hedman, M. C. Ferris, R. P. O’Neill, E. B. Fisher, and S. S. Oren, “Co-optimization of generation unit commitment and transmission switching with N-1 reliability,” IEEE Transactions on Power Systems, vol. 25, no. 2, pp. 1052-1063, May 2010.
[5] M. Sahraei-Ardakani; K. W. Hedman, "A Fast LP Approach for Enhanced Utilization of Variable Impedance Based FACTS Devices," in IEEE Transactions on Power Systems , vol.PP, no.99, pp.1-10

MIP cplex:
[6] E. B. Fisher, R. P. O'Neill and M. C. Ferris, "Optimal Transmission Switching," in IEEE Transactions on Power Systems, vol. 23, no. 3, pp. 1346-1355, Aug. 2008.

Decomposition Methods:
[7] Villumsen, Jonas Christoffer, and Andy B. Philpott. "Column generation for transmission switching of electricity networks with unit commitment." Lecture Notes in Engineering and Computer Science 2189 (2011): 1440-1443.
[8] Villumsen, Jonas Christoffer, Geir Bronmo, and Andy B. Philpott. "Line capacity expansion and transmission switching in power systems with large-scale wind power." Power Systems, IEEE Transactions on 28.2 (2013): 731-739.

MINLP:
[9] Coffrin, C., Hijazi, H. L., Lehmann, K., Van Hentenryck, P. "Primal and dual bounds for optimal transmission switching." Power Systems Computation Conference (PSCC), 2014. IEEE, 2014.

Technology
Smartwires company provides incremental line impedance control, which when aggregated across the line, can change power flows and cause:
Congestion/Uplift Reduction
Phase Balancing
Grid Resiliency
smartwire: http://www.smartwires.com/
They are using plexus to find the optimal location of the impedance in the system using LPs

Software:
- PowerTools by Hijazi
http://hhijazi.github.io/PowerTools/

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