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##### The Concept of Topology Control Using Line Switching

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**The Concept of Topology Control Using Line Switching**ShmuelOren Earl J. Isaac Professor University of California at Berkeley**Overview**• Overview of RATC • Topology Control’s Impact on the Feasible Set of Dispatch Solutions • Industry Practices of Topology Control • RATC Solutions • Topology Control and Reliability • Previous Topology Control Research: Economic Savings**National Directives**• Federal Energy Regulatory Commission (FERC) Order 890 • Improve the economic operations of the electric transmission grid • Energy Policy Act of 2005 • Sec.1223.a.5 of the US Energy Policy Act of 2005 • “encourage… deployment of advanced transmission technologies” • “optimized transmission line configuration” • Energy Independence and Security Act of 2007 • Title 13, Smart Grid: • “increased use of … controls technology to improve reliability, stability, and efficiency of the grid” • “dynamic optimization of grid operations and resources”**Motivation for Topology Control**• Control of transmission not fully utilized today • Transmission assets are treated as static in the short term • Currently operators change transmission assets’ states on ad-hoc basis • Special Protection Schemes (SPSs) • Network redundancies • Required for reliability • Each redundancy not required for every operational state • Redundancies may cause dispatch inefficiency • Harness the flexibility of transmission assets for power flow control • Improvements in reliability • Co-optimize with generation to reduce costs • Loss minimization • Congestion management**Literature Review**Corrective switching • [Mazi, Wollenberg, Hesse 1986]: Corrective control of power systems flows • [Schnyder, Glavitsch 1990]: Security enhancement using an optimal switching power flow • [Shao, Vittal 2006]: Corrective switching algorithm for relieving overloads and voltage violations Switching to reduce losses • [Fliscounakis, Zaoui, et al. 2007]: Topology influence on loss reduction as a mixed integer linear program Switching to relieve congestion • [Granelli, Montagna, et al. 2006]: Optimal network reconfiguration for congestion management by deterministic and genetic algorithms Switching to ensure stability • [Perunicic, Ilic, Stankovic1988]: Short time stabilization of power systems vial line switching**Section 2: Topology Control’s Impact on the Feasible Set**of Dispatch Solutions**Topology Control and the Feasible Set of Dispatch Solutions**• Solution space for optimal power flow • Original feasible set: {0, 1, 2, 3} • Original optimal cost: $20,000(A=180MW,B=30MW,C=40MW) at {2} Original Feasible Set Gen B Optimal Solution 120MW 1 80MW 50MW 30MW 2 Gen A 3 0 180MW 150MW 200MW**Topology Control and the Feasible Set of Dispatch Solutions**• Feasible set with line A-B offline: {0, 4, 5, 6} • With topology control: feasible set: {0, 1, 7, 5, 6} • Non-convex set – causes difficulty to solve topology control problems • Open Line A-B, optimal cost: $15,000 (A=200MW, B=50MW) at {8} Gen B Feasible Set with Line A-1 Offline Optimal Solution with Topology Control 120MW 1 80MW 4 7 5 50MW 8 30MW 2 Gen A 3 0 6 180MW 150MW 200MW**Special Protection Schemes (Remedial Action Schemes)**• PJM (2010) Manual 3: Transmission Operations. http://www.pjm.com/markets-and-operations/compliance/nerc-standards/~/media/documents/manuals/m03.ashx • Sunnyside-Torrey 138 kV Operating Guide (AEP Operating Memo T029) • Historically, the Sunnyside-Torrey 138 kV overloads on the outage of the South Canton – Torrey 138 kV line. Opening the S.E. Canton 138 kV CB at Sunnyside will help to reduce the post-contingency flow on the Sunnyside-Torrey 138 kV line. • Page 107**Special Protection Schemes (Remedial Action Schemes)**• PJM (2010) Manual 3 • The 138 kV tieline L28201 from Zion to Lakeview (WEC) can be opened to relieve contingency overloads for the loss of either of the following two lines: • Zion Station 22 to Pleasant Prairie (WEC) 345 kV Red (L2221) • Zion Station 22 to Arcadian (WEC) 345 kV Blue (L2222) • Page 172 • 107_Dixon ‗L15621‘ 138 kV CB Operation (ComEd SPOG 3-21) • The L15621 138 kV circuit breaker at Dixon may be opened to reduce post-contingency loadings on the Nelson – Dixon (15508) 138 kV line for the loss of the Nelson – Dixon (15507) 138 kV line if the contingency occurs. • Page 173**Superstorm Sandy - PJM**• PJM lost 82 bulk electric facilities • 6 500kV facilities; 3 345kV facilities; 39 230kV facilities; 25 138kV facilities • Caused extremely high voltage on the system during low load levels • “We were dealing with extremely high voltage on the system but a switching plan was developed to help alleviate these conditions.” • Via Andy Ott, VP of PJM: several 500kV lines were switched out to mitigate over voltage concerns during these low load level periods**Topology Control for Congestion Management**• California ISO, Minimum Effective Threshold Report. [Online]. Page 4. Available: http://www.caiso.com/274c/274ce77df630.pdf. • Event causedsubstantial congestion in 115kV network in Sacramento Valley • “These constraints resulted from outages in the higher voltage transmission system running north-to-south through the Sacramento Valley; the ISO had multiple days around this time when this 115 kV transmission system had significant congestion costs due to the north-to-south flows, until the ISO was able to later identify a remedy of transmission circuit switching to relieve this congestion.” • Took 2 weeks to determine this switching solution**Manage Congestion in Germany to Mitigate Wind Intermittency**• F. Kuntz, “Congestion management in Germany – the impact of renewable generation on congestion management costs,” Available: http://idei.fr/doc/conf/eem/papers_2011/kunz.pdf. • Use of transmission switching to mitigate line overloads caused by intermittent resources**Current Industry Practices**• While there are current industry practices of topology control there is yet a systematic framework to optimize the network topology • Not a part of day-ahead operations • Not a part of hour-ahead operations • No real-time corrective switching optimization**New Challenges and Opportunities**• Challenge: Renewables, N-m Events and Malicious Attacks • New opportunities: • Advances in computational capabilities (hardware and software) • Aid the transition from preventive to corrective control**New Challenges: Renewables**• Renewables (wind and solar): • Variable & uncertain – frequently changing flow patterns • Require additional conventional generators to be committed in order to provide reserves • Complications: • Renewables are frequently remotely located • Congestion • Renewables not only require more reserves but require additional locational reserves**Current Solutions to Manage Renewables**• Dispatch more conventional, fossil-fuel based generation • Drawbacks: • Generators operate at inefficient levels • Generators are required to provide fast ramping services • Additional investment in generation to provide locational reserves • Emissions per MWh increase due to operating at inefficient levels and fast ramping • Defeats the economic and environmental benefits of renewables! • Increase demand response programs • Difficult to ensure consumers curtail load when needed • Percent of continued participation in these programs is not high**The RATC Solution**• Current approaches utilize two types of assets: • Generation and Demand • Current approaches neglect the utilization of the transmission grid • Topology control has primarily been out of reach due to computational complexity • Robust Adaptive Topology Control enables: • Modeling of transmission assets (lines and transformers) as a controllable asset • Topology control: • Re-directs flow of electric power by temporarily reconfiguring the topology • Use of circuit breakers – low hardware cost solution • Improves deliverability of reserves**New Challenges: N-m Contingencies & Malicious Attacks**• Cascading outages and malicious attacks: • Extreme social welfare losses due to lost load The RATC Solution: • Topology detection procedure – determines lines out of service without faults • Fast re-closure algorithm to minimize load shedding and bring the system back to steady-state**New Challenges: Paradigm Shift from Preventive to Corrective**• Primary method to ensure N-1 reliable operations is preventive approach The RATC Solution: • Fast algorithms to implement corrective switching • Enables topology control to be used to respond to N-1 events • Improves reliability and reduces operational costs**Generator Info**• Operational costs, startup costs, shutdown costs, min & max operating levels, ramp rates • N-1 is enforced • System must have adequate 10 minute spinning reserve online to respond to any contingency (line or generator)**Optimal Solutions & Impact on Reliability**• Optimal N-1 compliant solution with static topology: • Solution cannot handle loss of generators 3 and 4 • Optimal N-1 compliant solution with smart switching (line A-C open) • Solution can handle loss of generators 3 and 4**Section 6: Previous Topology Control Research: Economic**Savings