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Grid oscillation
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<h2 id="terminology">Terminology</h2> <p><a href="/facts/North_American_Electric_Reliability_Corporation/AtSDgddP">North American Electric Reliability Corporation</a> suggested the following classification for the grid oscillations:<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <ul><li>System (Natural): low-frequency changes in the <a href="/facts/Rotor_angle/6rBUuJkI">rotor angle</a> triggered by power <a href="/facts/Grid_balancing/ACUNKJHh">imbalance</a>: <ul><li>Local: oscillations of a generator caused by heavy load interacting with the generator control</li> <li>Intra-plant: oscillations between units within a power plant caused by unit control interactions and poor control settings</li> <li>Inter-area: oscillations between few coherent parts of the system due to weak inter-area <a href="/facts/Tie_line_(electrical_grid)/Qrr0LLgk">tie lines</a> (0.15–1.00 Hz)</li> <li>Torsional: relatively high (but still below <a href="/facts/Line_frequency/hd4jVcSk">line frequency</a>, "subsynchronous") due to resonance between transmission lines with high level of <a href="/facts/Voltage_compensation/PIJfGtzr">voltage compensation</a> and the mechanical resonances of <a href="/facts/Turbine_generator/5sATsUGX">turbine generators</a> (also known as subsynchronous resonance, 5.00–50.00 Hz)</li></ul></li> <li>Forced: oscillations due to externally injected forced, like faulty equipment.</li></ul> <h2 id="history">History</h2> <p>The oscillations are inherent in a synchronous electrical power system. Oversimplified, a synchronous generator behaves like a <a href="/facts/Pendulum/D2hQXwlI">pendulum</a>, with synchronizing torque playing the role of gravity by pulling the machine into synchronicity, and the inertia of the rotor causing the generator to overshoot the ideal synchronized <a href="/facts/Rotor_angle/6rBUuJkI">rotor angle</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> The oscillations were therefore immediately discovered once multiple generators were connected in parallel to increase power and reliability. At the time, the generators were close together, the oscillation frequencies were on the order of 1-2 Hz, and a <a href="/facts/Damper_winding/mtmv5qpc">damper winding</a> was added to the design in order to absorb the energy of oscillations.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>As the power systems grew in size, rapid <a href="/facts/Automatic_voltage_control/RWQATaje">automatic voltage control</a> was introduced. The fast feedback of these systems had a side effect of lower damping, so power system stabilizers (PSS) were added to damp the oscillations. In the 1950 and 1960, the electric power industry consolidated the grids into larger and larger ones for reliability and savings of scale. However, oscillations became a major issue, and some interconnections were actually abandoned until asynchronous means of connecting systems arrived in the form of <a href="/facts/HVDC/FDIob86A">HVDC</a> links.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h2 id="sources">Sources</h2> <ul><li>Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1"><i>Power System Oscillations: An Introduction to Oscillation Analysis and Control</i></a>. Springer Nature. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-3-031-80581-3. Retrieved 2025-04-29.</li> <li>NERC (September 2017). <a href="https://web.archive.org/web/20220605051040/https://www.nerc.com/comm/PC_Reliability_Guidelines_DL/Reliability_Guideline_-_Forced_Oscillations_-_2017-07-31_-_FINAL.pdf">"Reliability Guideline Forced Oscillation Monitoring & Mitigation"</a> (PDF). Archived from <a href="https://www.nerc.com/comm/PC_Reliability_Guidelines_DL/Reliability_Guideline_-_Forced_Oscillations_-_2017-07-31_-_FINAL.pdf">the original</a> (PDF) on 5 June 2022.</li> <li>Wang, Bin (May 13, 2021). <a href="https://www.nrel.gov/docs/fy21osti/79994.pdf"><i>Demystifying Power System Oscillations – Recent and Ongoing Efforts</i></a> (PDF). 2021 Joint Synchronized Information Subcommittee (JSIS) Meeting. Grid Planning and Analysis Center, <a href="/facts/National_Renewable_Energy_Laboratory/UMhnJKEC">National Renewable Energy Laboratory</a> (NREL).</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Rogers et al. 2025, pp. 1–2. - Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). Power System Oscillations: An Introduction to Oscillation Analysis and Control. Springer Nature. ISBN 978-3-031-80581-3. Retrieved 2025-04-29. <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1" target="_blank">https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Rogers et al. 2025, p. 2. - Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). Power System Oscillations: An Introduction to Oscillation Analysis and Control. Springer Nature. ISBN 978-3-031-80581-3. Retrieved 2025-04-29. <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1" target="_blank">https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Wang 2021, p. 2. - Wang, Bin (May 13, 2021). Demystifying Power System Oscillations – Recent and Ongoing Efforts (PDF). 2021 Joint Synchronized Information Subcommittee (JSIS) Meeting. Grid Planning and Analysis Center, National Renewable Energy Laboratory (NREL). <a href="https://www.nrel.gov/docs/fy21osti/79994.pdf" target="_blank">https://www.nrel.gov/docs/fy21osti/79994.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Rogers et al. 2025, pp. 2–3. - Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). Power System Oscillations: An Introduction to Oscillation Analysis and Control. Springer Nature. ISBN 978-3-031-80581-3. Retrieved 2025-04-29. <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1" target="_blank">https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>NERC 2017, pp. 5, 8. - NERC (September 2017). "Reliability Guideline Forced Oscillation Monitoring & Mitigation" (PDF). Archived from the original (PDF) on 5 June 2022. <a href="https://web.archive.org/web/20220605051040/https://www.nerc.com/comm/PC_Reliability_Guidelines_DL/Reliability_Guideline_-_Forced_Oscillations_-_2017-07-31_-_FINAL.pdf" target="_blank">https://web.archive.org/web/20220605051040/https://www.nerc.com/comm/PC_Reliability_Guidelines_DL/Reliability_Guideline_-_Forced_Oscillations_-_2017-07-31_-_FINAL.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Rogers et al. 2025, p. 1. - Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). Power System Oscillations: An Introduction to Oscillation Analysis and Control. Springer Nature. ISBN 978-3-031-80581-3. Retrieved 2025-04-29. <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1" target="_blank">https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Rogers et al. 2025, p. 2. - Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). Power System Oscillations: An Introduction to Oscillation Analysis and Control. Springer Nature. ISBN 978-3-031-80581-3. Retrieved 2025-04-29. <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1" target="_blank">https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Rogers et al. 2025, p. 2. - Rogers, Graham; Elliott, Ryan T.; Trudnowski, Daniel J.; Wilches-Bernal, Felipe; Osipov, Denis; Chow, Joe H. (2025-02-03). Power System Oscillations: An Introduction to Oscillation Analysis and Control. Springer Nature. ISBN 978-3-031-80581-3. Retrieved 2025-04-29. <a href="https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1" target="_blank">https://www.google.com/books/edition/Power_System_Oscillations/14BDEQAAQBAJ?hl=en&gbpv=1&pg=PA1</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> </ol>