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Contingency (electrical grid)
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<h2 id="contingency-analysis">Contingency analysis</h2> <p>The contingency analysis application periodically runs on the computers at the operations centers providing suggestions to the operators based on the current state of the grid and the <i>contingency selection</i>.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The software provides answers to the "what if" scenarios in the form of "alarms": "Loss of component X will result in overload of Y by Z%".<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> By the 1990s analysis of a large interconnected system involved testing of many thousands of contingency events (millions if double contingencies were considered). An effect of each contingency requires performing a <a href="/facts/Power_flow/QbMNhIbM">power flow</a> calculation. Due to the rapid change of the state of a power system the run of the application shall complete in minutes (up to 30<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>) for the results to be useful.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Typically only selected contingencies, mostly single ones with some double ones are considered to speed up the process. The selection of contingencies is using engineering judgment to choose the ones most likely to cause problems.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <h3>Credible contingencies</h3> <p>The foreseen and analyzed contingencies are called <i>credible</i>. Examples of these are failures of:<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> <ul><li>a transmission line or <a href="/facts/Tie_line_(electrical_grid)/Qrr0LLgk">tie line</a> / <a href="/facts/HVDC_link/FDIob86A">HVDC link</a>;</li> <li>a generator;</li> <li>a transformer;</li> <li>a <a href="/facts/Variable_renewable_energy/kynTl1t2">variable renewable energy</a> cluster;</li> <li>a <a href="/facts/Voltage_compensation/PIJfGtzr">voltage compensation</a> device.</li></ul> <p>In continental Europe these contingencies are considered "normal", with "exceptional" credible contingencies being the failures of:<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <ul><li>a double circuit transmission line;</li> <li>two generators;</li> <li>a <a href="/facts/Bus_bar/Mdm9AF1S">bus bar</a>.</li></ul> <p>Non-credible (also called "out-of-range") contingencies are not used in planning, as they are rare and their effects are hard to predict, for example, failures of:<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <ul><li>an entire <a href="/facts/Electrical_substation/Iy8NeYzy">electrical substation</a>;</li> <li>a <a href="/facts/Transmission_tower/snFJ3do3">transmission tower</a> that carries more than two lines.</li></ul> <h2 id="n-x-contingency-planning">N-X contingency planning</h2> <p>Reliability of the energy supply usually requires that any single major unit failure leaves the system with enough resources to supply the current load. The system that satisfies this requirement is described as meeting the N-1 contingency criterion (N designates the number of pieces of equipment). The N-2 and N-3 contingency refers to planning for a simultaneous loss of, respectively, 2 or 3 major units; this is sometimes done for the critical area (e.g. <a href="/facts/Downtown/WvmTHvTE">downtown</a>).<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> The term "N-1 security assessment" is also used.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> </p><p>The N-1 requirement is used throughout the network, from generation to <a href="/facts/Electrical_substation/Iy8NeYzy">substations</a>. At the <a href="/facts/Power_distribution/F5NfTeWP">distribution</a> level, however, the planners frequently allow a more relaxed interpretation: a single failure should ensure uninterrupted delivery of power to almost all the customers at least at the "emergency level" (Range B of the ANSI C84.1<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a>), but a small section of the network that contains the original fault might require <i>manual switching</i> with a service interruption for about an hour.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> </p><p>The popularity of <i>contingency planning</i> is based on its advantages: </p> <ul><li>each of the N elements in the system is analyzed separately, limiting the amount of work to be done and simplifying the failure options (e.g., generator failure, short circuit);</li> <li>the process inherently provides a way to deal with the contingency if and when it will happen.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a></li></ul> <p>The N-1 contingency planning is typically sufficient for the systems with the usual ratio of peak load to capacity (below 70%). For a system with a substantially higher ratio, the N-1 planning will not deliver satisfactory reliability, and even N-2 and N-3 criteria might not be sufficient; therefore the <i>reliability-based planning</i> is used that considers the probabilities of the individual contingencies.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p><p>N-1-1 contingency is defined as a single fault followed by manual recovery procedures, with another fault occurring after the successful recovery from the first failure. Normal operating conditions are sometimes referred to as N-0.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> </p> <h2 id="seel-also">Seel also</h2> <ul><li><a href="/facts/Power_system_protection/gX2g5TNH">Power system protection</a></li></ul> <h2 id="sources">Sources</h2> <ul><li>Willis, H. Lee (1 March 2004). <a href="https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499">"Contingency-based planning criteria"</a>. <i>Power Distribution Planning Reference Book, Second Edition</i> (2 ed.). CRC Press. pp. 499–500. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-4200-3031-0.</li> <li>Wood, Allen J.; Wollenberg, Bruce F. (1984). <a href="https://books.google.com/books?id=dwRtAAAAIAAJ"><i>Power Generation, Operation, and Control</i></a>. John Wiley & Sons. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-471-09182-0. <a href="/facts/OCLC_(identifier)/Yqad8waq">OCLC</a> <a href="https://search.worldcat.org/oclc/1085785794">1085785794</a>.</li> <li>Pavella, Mania; Ernst, Damien; Ruiz-Vega, Daniel (6 December 2012). <a href="https://books.google.com/books?id=3hPpBwAAQBAJ&pg=PA6"><i>Transient Stability of Power Systems: A Unified Approach to Assessment and Control</i></a>. Springer Science & Business Media. pp. 6–. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-4615-4319-0. <a href="/facts/OCLC_(identifier)/Yqad8waq">OCLC</a> <a href="https://search.worldcat.org/oclc/44650996">44650996</a>.</li> <li>Balu, N.; Bertram, T.; Bose, A.; Brandwajn, V.; Cauley, G.; Curtice, D.; Fouad, A.; Fink, L.; Lauby, M.G.; Wollenberg, B.F.; Wrubel, J.N. (1992). <a href="https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf">"On-line power system security analysis"</a> (PDF). <i>Proceedings of the IEEE</i>. 80 (2): 262–282. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1109%2F5.123296">10.1109/5.123296</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/0018-9219">0018-9219</a>.</li> <li>Hadjsaid, Nouredine (19 December 2017). <a href="https://books.google.com/books?id=zrPMBQAAQBAJ&pg=SA24-PA1">"Security Analysis"</a>. In Leonard L. Grigsby (ed.). <i>Power System Stability and Control</i> (3 ed.). CRC Press. pp. 24-1 to 24-?. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-4398-8321-1.</li> <li>Heylen, Evelyn; De Boeck, Steven; Ovaere, Marten; Ergun, Hakan; Van Hertem, Dirk (26 January 2018). <a href="https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21">"Steady-State Security"</a>. <i>Dynamic Vulnerability Assessment and Intelligent Control for Sustainable Power Systems</i>. John Wiley & Sons, Ltd. pp. 21–40. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1002%2F9781119214984.ch2">10.1002/9781119214984.ch2</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-119-21495-3.</li> <li>Wang, Lei; Lin, Xi; Howell, Fred; Morison, Kip (2016). <a href="https://books.google.com/books?id=iBUWCgAAQBAJ&pg=PA268">"Dynamic Security Assessment"</a>. <i>Smart Grid Handbook, 3 Volume Set</i>. John Wiley & Sons, Ltd. pp. 265–287. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1002%2F9781118755471.sgd090">10.1002/9781118755471.sgd090</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-118-75548-8.</li> <li>IBRR (2016). "State Estimation and N-1 Security Assessment". <a href="https://documents.worldbank.org/curated/en/779591468187450158/pdf/103719-WP-P131558-PUBLIC-VN-Smart-Grid-Book-2-21-16.pdf"><i>Smart Grid to Enhance Power Transmission in Vietnam</i></a> (PDF). Washington, DC: International Bank for Reconstruction and Development/The World Bank. pp. 65–66.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>NERC (December 2, 2022). "Glossary of Terms Used in NERC Reliability Standards" (PDF). nerc.com. North American Electric Reliability Corporation. <a href="https://www.nerc.com/pa/Stand/Glossary%20of%20Terms/Glossary_of_Terms.pdf" target="_blank">https://www.nerc.com/pa/Stand/Glossary%20of%20Terms/Glossary_of_Terms.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Pavella, Ernst & Ruiz-Vega 2012, p. 6. - Pavella, Mania; Ernst, Damien; Ruiz-Vega, Daniel (6 December 2012). Transient Stability of Power Systems: A Unified Approach to Assessment and Control. Springer Science & Business Media. pp. 6–. ISBN 978-1-4615-4319-0. OCLC 44650996. <a href="https://books.google.com/books?id=3hPpBwAAQBAJ&pg=PA6" target="_blank">https://books.google.com/books?id=3hPpBwAAQBAJ&pg=PA6</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Balu et al. 1992, p. 268. - Balu, N.; Bertram, T.; Bose, A.; Brandwajn, V.; Cauley, G.; Curtice, D.; Fouad, A.; Fink, L.; Lauby, M.G.; Wollenberg, B.F.; Wrubel, J.N. (1992). "On-line power system security analysis" (PDF). Proceedings of the IEEE. 80 (2): 262–282. doi:10.1109/5.123296. ISSN 0018-9219. <a href="https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf" target="_blank">https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Heylen et al. 2018, p. 25. - Heylen, Evelyn; De Boeck, Steven; Ovaere, Marten; Ergun, Hakan; Van Hertem, Dirk (26 January 2018). "Steady-State Security". Dynamic Vulnerability Assessment and Intelligent Control for Sustainable Power Systems. John Wiley & Sons, Ltd. pp. 21–40. doi:10.1002/9781119214984.ch2. ISBN 978-1-119-21495-3. <a href="https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21" target="_blank">https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Wood & Wollenberg 1984, p. 357. - Wood, Allen J.; Wollenberg, Bruce F. (1984). Power Generation, Operation, and Control. John Wiley & Sons. ISBN 978-0-471-09182-0. OCLC 1085785794. <a href="https://books.google.com/books?id=dwRtAAAAIAAJ" target="_blank">https://books.google.com/books?id=dwRtAAAAIAAJ</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Pavella, Ernst & Ruiz-Vega 2012, p. 6. - Pavella, Mania; Ernst, Damien; Ruiz-Vega, Daniel (6 December 2012). Transient Stability of Power Systems: A Unified Approach to Assessment and Control. Springer Science & Business Media. pp. 6–. ISBN 978-1-4615-4319-0. OCLC 44650996. <a href="https://books.google.com/books?id=3hPpBwAAQBAJ&pg=PA6" target="_blank">https://books.google.com/books?id=3hPpBwAAQBAJ&pg=PA6</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Wood & Wollenberg 1984, p. 357. - Wood, Allen J.; Wollenberg, Bruce F. (1984). Power Generation, Operation, and Control. John Wiley & Sons. ISBN 978-0-471-09182-0. OCLC 1085785794. <a href="https://books.google.com/books?id=dwRtAAAAIAAJ" target="_blank">https://books.google.com/books?id=dwRtAAAAIAAJ</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Balu et al. 1992, p. 268. - Balu, N.; Bertram, T.; Bose, A.; Brandwajn, V.; Cauley, G.; Curtice, D.; Fouad, A.; Fink, L.; Lauby, M.G.; Wollenberg, B.F.; Wrubel, J.N. (1992). "On-line power system security analysis" (PDF). Proceedings of the IEEE. 80 (2): 262–282. doi:10.1109/5.123296. ISSN 0018-9219. <a href="https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf" target="_blank">https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Hadjsaid 2017, p. 24-3. - Hadjsaid, Nouredine (19 December 2017). "Security Analysis". In Leonard L. Grigsby (ed.). Power System Stability and Control (3 ed.). CRC Press. pp. 24-1 to 24-?. ISBN 978-1-4398-8321-1. <a href="https://books.google.com/books?id=zrPMBQAAQBAJ&pg=SA24-PA1" target="_blank">https://books.google.com/books?id=zrPMBQAAQBAJ&pg=SA24-PA1</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Balu et al. 1992, p. 269. - Balu, N.; Bertram, T.; Bose, A.; Brandwajn, V.; Cauley, G.; Curtice, D.; Fouad, A.; Fink, L.; Lauby, M.G.; Wollenberg, B.F.; Wrubel, J.N. (1992). "On-line power system security analysis" (PDF). Proceedings of the IEEE. 80 (2): 262–282. doi:10.1109/5.123296. ISSN 0018-9219. <a href="https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf" target="_blank">https://home.engineering.iastate.edu/~jdm/ee554/Security1992.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Hadjsaid 2017, p. 24-3. - Hadjsaid, Nouredine (19 December 2017). "Security Analysis". In Leonard L. Grigsby (ed.). Power System Stability and Control (3 ed.). CRC Press. pp. 24-1 to 24-?. ISBN 978-1-4398-8321-1. <a href="https://books.google.com/books?id=zrPMBQAAQBAJ&pg=SA24-PA1" target="_blank">https://books.google.com/books?id=zrPMBQAAQBAJ&pg=SA24-PA1</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Heylen et al. 2018, p. 25. - Heylen, Evelyn; De Boeck, Steven; Ovaere, Marten; Ergun, Hakan; Van Hertem, Dirk (26 January 2018). "Steady-State Security". Dynamic Vulnerability Assessment and Intelligent Control for Sustainable Power Systems. John Wiley & Sons, Ltd. pp. 21–40. doi:10.1002/9781119214984.ch2. ISBN 978-1-119-21495-3. <a href="https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21" target="_blank">https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Heylen et al. 2018, p. 25. - Heylen, Evelyn; De Boeck, Steven; Ovaere, Marten; Ergun, Hakan; Van Hertem, Dirk (26 January 2018). "Steady-State Security". Dynamic Vulnerability Assessment and Intelligent Control for Sustainable Power Systems. John Wiley & Sons, Ltd. pp. 21–40. doi:10.1002/9781119214984.ch2. ISBN 978-1-119-21495-3. <a href="https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21" target="_blank">https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Heylen et al. 2018, p. 25. - Heylen, Evelyn; De Boeck, Steven; Ovaere, Marten; Ergun, Hakan; Van Hertem, Dirk (26 January 2018). "Steady-State Security". Dynamic Vulnerability Assessment and Intelligent Control for Sustainable Power Systems. John Wiley & Sons, Ltd. pp. 21–40. doi:10.1002/9781119214984.ch2. ISBN 978-1-119-21495-3. <a href="https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21" target="_blank">https://books.google.com/books?id=YbVIDwAAQBAJ&pg=PA21</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Willis 2004, p. 499. - Willis, H. Lee (1 March 2004). "Contingency-based planning criteria". Power Distribution Planning Reference Book, Second Edition (2 ed.). CRC Press. pp. 499–500. ISBN 978-1-4200-3031-0. <a href="https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499" target="_blank">https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>IBRR 2016, pp. 65–66. - IBRR (2016). "State Estimation and N-1 Security Assessment". Smart Grid to Enhance Power Transmission in Vietnam (PDF). Washington, DC: International Bank for Reconstruction and Development/The World Bank. pp. 65–66. <a href="https://documents.worldbank.org/curated/en/779591468187450158/pdf/103719-WP-P131558-PUBLIC-VN-Smart-Grid-Book-2-21-16.pdf" target="_blank">https://documents.worldbank.org/curated/en/779591468187450158/pdf/103719-WP-P131558-PUBLIC-VN-Smart-Grid-Book-2-21-16.pdf</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>ANSI. "Table 1". American National Standard for Electric Power Systems and Equipment — Voltage Ratings (60 Hertz) (PDF). American National Standards Institute. <a href="https://durastudio.com/sites/default/files/ansi_c84-1-20xx_2016_revision_draft_2019-02-15.pdf" target="_blank">https://durastudio.com/sites/default/files/ansi_c84-1-20xx_2016_revision_draft_2019-02-15.pdf</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Willis 2004, p. 499. - Willis, H. Lee (1 March 2004). "Contingency-based planning criteria". Power Distribution Planning Reference Book, Second Edition (2 ed.). CRC Press. pp. 499–500. ISBN 978-1-4200-3031-0. <a href="https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499" target="_blank">https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Willis 2004, p. 499. - Willis, H. Lee (1 March 2004). "Contingency-based planning criteria". Power Distribution Planning Reference Book, Second Edition (2 ed.). CRC Press. pp. 499–500. ISBN 978-1-4200-3031-0. <a href="https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499" target="_blank">https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Willis 2004, p. 499. - Willis, H. Lee (1 March 2004). "Contingency-based planning criteria". Power Distribution Planning Reference Book, Second Edition (2 ed.). CRC Press. pp. 499–500. ISBN 978-1-4200-3031-0. <a href="https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499" target="_blank">https://books.google.com/books?id=9EShPwTRnoUC&pg=PA499</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Wang et al. 2016, p. 268. - Wang, Lei; Lin, Xi; Howell, Fred; Morison, Kip (2016). "Dynamic Security Assessment". Smart Grid Handbook, 3 Volume Set. John Wiley & Sons, Ltd. pp. 265–287. doi:10.1002/9781118755471.sgd090. ISBN 978-1-118-75548-8. <a href="https://books.google.com/books?id=iBUWCgAAQBAJ&pg=PA268" target="_blank">https://books.google.com/books?id=iBUWCgAAQBAJ&pg=PA268</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> </ol>