Electricity Breakdown Essay

This article is about accidental power failures. For intentionally engineered ones, see rolling blackout.

A power outage (also called a power cut, a power blackout, power failure or a blackout) is a short-term or a long-term loss of the electric power to a particular area.

There are many causes of power failures in an electricity network. Examples of these causes include faults at power stations, damage to electric transmission lines, substations or other parts of the distribution system, a short circuit, or the overloading of electricity mains.

Power failures are particularly critical at sites where the environment and public safety are at risk. Institutions such as hospitals, sewage treatment plants, mines, shelters and the like will usually have backup power sources such as standby generators, which will automatically start up when electrical power is lost. Other critical systems, such as telecommunication, are also required to have emergency power. The battery room of a telephone exchange usually has arrays of lead–acid batteries for backup and also a socket for connecting a generator during extended periods of outage.

Types of power outage[edit]

Power outages are categorized into three different phenomena, relating to the duration and effect of the outage:

  • A permanent fault is a massive loss of power typically caused by a fault on a power line. Power is automatically restored once the fault is cleared.
  • A brownout is a drop in voltage in an electrical power supply. The term brownout comes from the dimming experienced by lighting when the voltage sags. Brownouts can cause poor performance of equipment or even incorrect operation.
  • A blackout is the total loss of power to an area and is the most severe form of power outage that can occur. Blackouts which result from or result in power stations tripping are particularly difficult to recover from quickly. Outages may last from a few minutes to a few weeks depending on the nature of the blackout and the configuration of the electrical network.

Protecting the power system from outages[edit]

In power supply networks, the power generation and the electrical load (demand) must be very close to equal every second to avoid overloading of network components, which can severely damage them. Protective relays and fuses are used to automatically detect overloads and to disconnect circuits at risk of damage.

Under certain conditions, a network component shutting down can cause current fluctuations in neighboring segments of the network leading to a cascading failure of a larger section of the network. This may range from a building, to a block, to an entire city, to an entire electrical grid.

Modern power systems are designed to be resistant to this sort of cascading failure, but it may be unavoidable (see below). Moreover, since there is no short-term economic benefit to preventing rare large-scale failures, researchers have expressed concern that there is a tendency to erode the resilience of the network over time, which is only corrected after a major failure occurs. In a 2003 publication, Carreras and co-authors claimed that reducing the likelihood of small outages only increases the likelihood of larger ones.[1] In that case, the short-term economic benefit of keeping the individual customer happy increases the likelihood of large-scale blackouts.

Protecting computer systems from power outages[edit]

Computer systems and other electronic devices containing logic circuitry are susceptible to data loss or hardware damage that can be caused by the sudden loss of power. These can include data networking equipment, video projectors, alarm systems as well as computers. To protect computer systems against this, the use of an uninterruptible power supply or 'UPS' can provide a constant flow of electricity if a primary power supply becomes unavailable for a short period of time. To protect against surges (events where voltages increase for a few seconds), which can damage hardware when power is restored, a special device called a surge protector that absorbs the excess voltage can be used.

Restoring power after a wide-area outage[edit]

Restoring power after a wide-area outage can be difficult, as power stations need to be brought back on-line. Normally, this is done with the help of power from the rest of the grid. In the total absence of grid power, a so-called black start needs to be performed to bootstrap the power grid into operation. The means of doing so will depend greatly on local circumstances and operational policies, but typically transmission utilities will establish localized 'power islands' which are then progressively coupled together. To maintain supply frequencies within tolerable limits during this process, demand must be reconnected at the same pace that generation is restored, requiring close coordination between power stations, transmission and distribution organizations.

Blackout inevitability and electric sustainability[edit]

Self-organized criticality[edit]

It has been argued on the basis of historical data[2] and computer modeling[3][4] that power grids are self-organized critical systems. These systems exhibit unavoidable[5] disturbances of all sizes, up to the size of the entire system. This phenomenon has been attributed to steadily increasing demand/load, the economics of running a power company, and the limits of modern engineering.[6] While blackout frequency has been shown to be reduced by operating it further from its critical point, it generally isn’t economically feasible, causing providers to increase the average load over time or upgrade less often resulting in the grid moving itself closer to its critical point. Conversely, a system past the critical point will experience too many blackouts leading to system-wide upgrades moving it back below the critical point. The term critical point of the system is used here in the sense of statistical physics and nonlinear dynamics, representing the point where a system undergoes a phase transition; in this case the transition from a steady reliable grid with few cascading failures to a very sporadic unreliable grid with common cascading failures. Near the critical point the relationship between blackout frequency and size follows a power-law distribution.[4][6]

Other leaders are dismissive of system theories that conclude that blackouts are inevitable, but do agree that the basic operation of the grid must be changed. The Electric Power Research Institute champions the use of smart grid features such as power control devices employing advanced sensors to coordinate the grid[7]. Others advocate greater use of electronically controlled high-voltage direct current (HVDC) firebreaks to prevent disturbances from cascading across AC lines in a wide area grid.[8]

Cascading failure becomes much more common close to this critical point. The power-law relationship is seen in both historical data and model systems.[6] The practice of operating these systems much closer to their maximum capacity leads to magnified effects of random, unavoidable disturbances due to aging, weather, human interaction etc. While near the critical point, these failures have a greater effect on the surrounding components due to individual components carrying a larger load. This results in the larger load from the failing component having to be redistributed in larger quantities across the system, making it more likely for additional components not directly affected by the disturbance to fail, igniting costly and dangerous cascading failures.[6] These initial disturbances causing blackouts are all the more unexpected and unavoidable due to actions of the power suppliers to prevent obvious disturbances (cutting back trees, separating lines in windy areas, replacing aging components etc.). The complexity of most power grids often makes the initial cause of a blackout extremely hard to identify.

Further information: Self-organized criticality control

OPA model[edit]

In 2002, researchers at Oak Ridge National Laboratory (ORNL), Power System Engineering Research Center of the University of Wisconsin (PSerc),[9] and the University of Alaska Fairbanks proposed a mathematical model for the behavior of electrical distribution systems.[10][11] This model has become known as the OPA model, a reference to the names of the authors' institutions. OPA is a cascading failure model. Other cascading failure models include Manchester, Hidden failure, CASCADE, and Branching.[12]

Mitigation of power outage frequency[edit]

The effects of trying to mitigate cascading failures near the critical point in an economically feasible fashion are often shown to not be beneficial and often even detrimental. Four mitigation methods have been tested using the OPA blackout model:[1]

  • Increase critical number of failures causing cascading blackouts – Shown to decrease the frequency of smaller blackouts but increase that of larger blackouts.
  • Increase individual power line max load – Shown to increase the frequency of smaller blackouts and decrease that of larger blackouts.
  • Combination of increasing critical number and max load of lines – Shown to have no significant effect on either size of blackout. The resulting minor reduction in the frequency of blackouts is projected to not be worth the cost of the implementation.
  • Increase the excess power available to the grid – Shown to decrease the frequency of smaller blackouts but increase that of larger blackouts.

In addition to the finding of each mitigation strategy having a cost-benefit relationship with regards to frequency of small and large blackouts, the total number of blackout events was not significantly reduced by any of the above-mentioned mitigation measures.[1]

A complex network-based model to control large cascading failures (blackouts) using local information only was proposed by A. E. Motter.[13]

One of the proposed solutions proposed to reduce the impact of power outage was introduced by M. Saleh.[14]

Key performance indicators[edit]

Utilities are measured on three specific performance measures:

See also[edit]

References[edit]

  1. ^ abcCarreras, B. A.; Lynch, V. E.; Newman, D. E.; Dobson, I. (2003). "Blackout mitigation assessment in power transmission systems". 36th Hawaii International Conference on System Sciences. Hawaii. 
  2. ^IEEE Computer Society Conference Publishing Services
  3. ^Microsoft Word – HICSS2002-paper2
  4. ^ abH. Hoffmann and D. W. Payton (2014). "Suppressing cascades in a self-organized-critical model with non-contiguous spread of failures"(PDF). Chaos, Solitons and Fractals. 67: 87–93. doi:10.1016/j.chaos.2014.06.011. 
  5. ^http://eceserv0.ece.wisc.edu/~dobson/PAPERS/carrerasHICSS00.pdf
  6. ^ abcdDobson et al. Complex systems analysis of series of blackouts: Cascading failure, critical points, and self-organization. Chaos 17, 2007.
  7. ^Saleh, M. S.; Althaibani, A.; Esa, Y.; Mhandi, Y.; Mohamed, A. A. (October 2015). "Impact of clustering microgrids on their stability and resilience during blackouts". 2015 International Conference on Smart Grid and Clean Energy Technologies (ICSGCE): 195–200. doi:10.1109/ICSGCE.2015.7454295. ISBN 978-1-4673-8732-3. 
  8. ^Peter Fairley (August 2004). "The Unruly Power Grid". IEEE Spectrum. Institute of Electrical and Electronics Engineers. 41 (8): 22. doi:10.1109/MSPEC.2004.1318179. Retrieved 2012-06-24. 
  9. ^"Power Systems Engineering Research Center". Board of Regents of the University of Wisconsin System. 2014. Retrieved 2015-06-23. 
  10. ^Carreras, B. A.; Lynch, V. E.; Dobson, I.; Newman, D. E. (2002). "Critical points and transitions in an electric power transmission model for cascading failure blackouts"(PDF). Chaos: an Interdisciplinary Journal of Nonlinear Science. 12 (4): 985. doi:10.1063/1.1505810. ISSN 1054-1500. 
  11. ^Dobson, I.; Carreras, B.A.; Lynch, V.E.; Newman, D.E. (2001). "Proceedings of the 34th Annual Hawaii International Conference on System Sciences": 710. doi:10.1109/HICSS.2001.926274. ISBN 0-7695-0981-9. 
  12. ^Nedic, Dusko P.; Dobson, Ian; Kirschen, Daniel S.; Carreras, Benjamin A.; Lynch, Vickie E. (2006). "Criticality in a cascading failure blackout model". International Journal of Electrical Power & Energy Systems. 28 (9): 627. doi:10.1016/j.ijepes.2006.03.006. 
  13. ^Motter, Adilson E. (2004). "Cascade Control and Defense in Complex Networks". Physical Review Letters. 93 (9). doi:10.1103/PhysRevLett.93.098701. 
  14. ^Saleh, M. S.; Althaibani, A.; Esa, Y.; Mhandi, Y.; Mohamed, A. A. (October 2015). "Impact of clustering microgrids on their stability and resilience during blackouts". 2015 International Conference on Smart Grid and Clean Energy Technologies (ICSGCE): 195–200. doi:10.1109/ICSGCE.2015.7454295. ISBN 978-1-4673-8732-3. 

External links[edit]

Tree limbs creating a short circuit in electrical lines during a storm. This typically results in a power outage in the area supplied by these lines

Viewpoint: Power to the Electrons

  • Georg Korn, ELI Beamlines, Institute of Physics of the Academy of Science, Czech Republic, 182 21 Prague 8, Czech Republic

Physics 7, 125

A laser-driven particle accelerator, delivering a beam of electrons with a record-breaking energy of 4.2 giga-electron-volts, could lead to compact x-ray lasers or high-energy colliders.

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Particle accelerators have had a profound impact on science and technology. They contributed to fundamental high-energy-physics experiments like those that revealed the Higgs boson, and are the basis of x-ray sources like synchrotrons and free-electron lasers—invaluable tools for materials sciences and biology. But their further development is hitting practical limits. Conventional schemes accelerate charged particles through the electric fields generated in radiofrequency (rf) cavities. Because of the electrical breakdown of such cavities, the accelerating field cannot exceed megavolts per meter (MV/m). This implies that future, higher-energy accelerators would have to be kilometers long and cost billions of dollars.

In the past decade, a possible alternative to conventional accelerator technologies has started to emerge. In a technique known as laser wakefield acceleration (LWFA), the interaction of short, intense laser pulses with a plasma can create accelerating electric fields of several hundred gigavolts per meter (GV/m). Within only few centimeters (cm) length, LWFA can generate beams of electrons with increasing energies, exceeding 1 giga-eletron-volts (GeV). Using a 9-cm-long plasma waveguide, the group of Wim Leemans at Lawrence Berkeley National Laboratory, California, has now demonstrated a scheme that delivers a high-quality electron beam with a record-breaking energy of [1]—in the same ballpark as the energy of the electrons running in many of today’s large-scale synchrotron facilities.

The LWFA technique, proposed 35 years ago by Dawson and Tajima [2], is based on the use of a short, intense laser pulse to induce density waves in a plasma. As the pulse propagates through the plasma, its electric field separates the plasma’s electrons from the ions. On the pulse trail, the displaced electrons feel an enormous electrostatic force pulling them back toward the heavier, barely moving, ions. This bubble of negative charges trails the laser pulse, moving through the plasma at about the speed of light and producing, in the laser pulse’s wake, a traveling longitudinal electric field that offers a steep acceleration gradient: for typical plasma electron densities (–), the resulting accelerating structure is only – long and can sustain fields of over , outperforming conventional acceleration structures based on superconducting rf cavities by 2–3 orders of magnitude [3]. Once electrons are injected in this plasma wakefield structure they can be accelerated to relativistic energies within very short distances.

The laser intensities needed for LWFA are extremely high, in the so-called relativistic regime (intensities above , which accelerate electrons to relativistic speeds). Laser plasma acceleration has thus been driven by technological advances that boosted laser peak and average power, together with stability, repetition rate (pulses emitted per second), and electrical efficiency. Such advances included the advent of diode-pumped solid-state lasers, which are more compact and efficient than flashlamp pumped lasers, and of chirped-pulse amplification (CPA) [4]—a technique in which ultrashort pulses are stretched out in time prior to amplification and compressed to the original duration after amplification. Recent LWFA experiments use CPA lasers with peak-powers in the 10-terawatt-to-petawatt range and pulse durations between tens and hundreds of femtoseconds, firing at a repetition rate of up to a few shots per second.

Several LWPA schemes have been successfully demonstrated that control, to different degrees, the plasma conditions, the electron bunch energy, and its energy spread. By optimizing electron injection mechanisms [5], researchers have been able to generate beams of extremely high quality, featuring a single well-defined energy of up to [6], small angular divergence and substantial charge in the electron bunches. Here, the authors realize a significant step forward in energy and efficiency. Using significantly less laser power than in the previous 2-GeV scheme, they accelerate electrons to the highest value obtained to date via lasers: .

The key to their success was the realization of a much longer interaction length than in previous demonstrations, thanks to a well-prepared guiding structure (see Fig. 1): a 9-cm-long capillary waveguide in which they used a pulsed electrical discharge, appropriately timed before the laser pulse, to preform a plasma channel. The team focused 40-fs laser pulses with 0.3-petawatt peak power into the capillary, to drive the self-injection regime (whereby cold electrons from the plasma are trapped and accelerated in the laser wake). The preformed plasma channel allowed fine control of the plasma density profile inside the waveguide (realizing a parabolic profile with smaller density in the center). Such guiding structure prevents diffractive breakup of the laser pulse, increasing the distance over which the laser intensity stays high. Maximum acceleration was achieved by careful optimization of experimental parameters. One of the key issues was finding optimum plasma conditions for guiding the laser pulse along the full length of the capillary: Guided by numerical modeling, the author chose an ideal plasma density of approximately [7]. Another essential optimization ingredient was the careful matching of the size of the laser focus to the preformed plasma channel.

The results of Leemans et al. can be regarded as a substantial advancement towards two grand goals of laser plasma acceleration sources. The first would be the realization of a linear electron-positron collider based on multiple LWFA stages. According to a recent proposal [8], a 1-tera-electron-volt (TeV) electron accelerator could be assembled with one hundred 10-GeV acceleration modules and combined with a similar 1-TeV positron accelerator to realize 2-TeV electron-positron collisions. Such a collider would be competitive with the International Linear Collider, a proposed facility based on conventional rf accelerators that, according to current designs, would have to be 30–50 kilometers long. In view of such a large-scale scheme, a major milestone posed by this work is the demonstrated efficiency increase, which substantially reduces the laser power needed to impart a given acceleration. Yet the development of such a collider will certainly take decades of hard work, as it requires substantial technological improvements both on the driving lasers and on the plasma-accelerator structures.

The second goal might be within closer reach. The demonstrated high-energy electron beam could be used to feed an x-ray free-electron laser (XFEL) that would fit into a university laboratory. In a FEL, high-energy electrons zigzag through a periodic arrangement of magnets, called an undulator, organizing themselves into microbunches that emit coherent, laserlike radiation. A laser-driven XFEL would be a very compact alternative (less than 30 m long [9]) to current kilometer-long XFELs like the LCLS or the European XFEL. Should tabletop XFELs become available, a vast number of applications, most notably the determination of the 3D structure of biomolecules [10], could be carried out by a much broader community of researchers, complementing large-scale facilities where beam time is expensive and scarce. Researchers have already demonstrated that laser-accelerated electrons, fed into undulators, can generate (incoherent) short pulse radiation at soft-x-ray wavelengths [11]. If the electrons can be made to emit x rays coherently, the device would turn into a FEL. It is reasonable to think that such a compact laser-driven XFEL could become a reality within the next decade.

Quite a few technological challenges remain. On the laser side, the increase of repetition rate would be useful for both FELs and accelerators to get sufficient photons and/or luminosity. Stability of the lasers will be key to get electron bunches that do not drift in position and energy. Diode-pumped solid-state lasers are key to this development, because they can better manage heating of the laser medium, and feature enhanced stability and electrical efficiency. Arrays of thousands of fiber lasers [12] could be a promising way to scale up the energy and bring the repetition rate well above 10 kilohertz. On the side of the plasma-accelerator stages, a better control of the electron energy spread they induce will be necessary for both FELs and colliders. But many of these obstacles will likely be overcome in coming years, in particular thanks to continuing advances in laser technology, which commercial and scientific applications drive at an extremely rapid pace.

References

  1. W. P. Leemans et al., “Multi-GeV Electron Beams from Capillary-Discharge-Guided Subpetawatt Laser Pulses in the Self-Trapping Regime,” Phys. Rev. Lett.113, 245002 (2014)
  2. T. Tajima and J. M. Dawson, “Laser Electron Accelerator,” Phys. Rev. Lett.43, 267 (1979)
  3. V. Malka et al., “Principles and Applications of Compact Laser-Plasma Accelerators,” Nature Phys.4, 447 (2008)
  4. D. Strickland and G. Mourou, “Compression of Amplified Chirped Optical Pulses,” Opt. Commun.56, 219 (1985)
  5. J. Faure et al., “Controlled Injection and Acceleration of Electrons in Plasma Wakefields by Colliding Laser Pulses,” Nature444, 737 (2006)
  6. X. Wang , et al. “Quasi-Monoenergetic Laser-Plasma Acceleration of Electrons to 2 GeV,” Nature Commun.4, 1988 (2013)
  7. In the present experiment, the beam’s top-hat spatial profile required higher density than that that would be needed for an ideal Gaussian profile
  8. W. P. Leemans and E. Esarey, “Laser-Driven Plasma-Wave Electron Accelerators,” Phys. Today62, No. 3, 44 (2009)
  9. See the ELI White Book, Science and Technology with High Intensity Lasers, edited by G. Mourou and G. Korn (http://www.eli-beams.eu/wp-content/uploads/2011/08/ELI-Book_neues_Logo-edited-web.pdf)
  10. M. Bergh, G. Huldt, N. Tîmneanu, F. R. Maia, and J. Hajdu, “Feasibility of Imaging Living Cells at Subnanometer Resolutions by Ultrafast X-Ray Diffraction,” Quart. Rev. Biophys.41, 181 (2008); R. Neutze, R. Wouts, D. van der Spoel, E. Weckert, and J. Hajdu, “Potential for Biomolecular Imaging with Femtosecond X-ray Pulses,” Nature406, 752 (2000)
  11. M. Fuchs et al., “Laser-Driven Soft-X-Ray Undulator Source,” Nature Phys.5, 826 (2009)
  12. G. Mourou, B. Brocklesby, T. Tajima, and J. Limpert, “The Future is Fibre Accelerators,” Nature Photon.7, 258 (2013)

About the Author

Georg Korn earned a Ph.D. in physics from the Institute for Optics and Spectroscopy, Academy of Sciences, Berlin, in 1983. After a postdoc at the Lebedev Physical Institute of the Russian Academy of Sciences, he worked at institutions such as the Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (Berlin), the Center for Ultrafast Optical Sciences University of Michigan, the University of California, San Diego, the Laboratoir d´Optique Appliquee (Palaiseau, France), the Max Planck Institute for Quantum Optics (Garching, Germany) as well as in the medical laser industry. He has carried out research on a wide range of topics in laser physics and technology, including lasers for fusion, laser-plasma interaction, laser-driven short-pulse x-ray generation, ultrafast and high-power lasers and lasers for material processing and vision correction. Since 2007 he has been the deputy coordinator of ELI (Extreme Light Infrastructure), a European high-power laser-facility project, and later became the chief scientist (2001) and the science and technology manager (2014) of the ELI Beamlines in Prague, Czech Republic. Georg Korn is a Fellow of the OSA and visiting professor at Osaka University.


Multi-GeV Electron Beams from Capillary-Discharge-Guided Subpetawatt Laser Pulses in the Self-Trapping Regime

W. P. Leemans, A. J. Gonsalves, H.-S. Mao, K. Nakamura, C. Benedetti, C. B. Schroeder, Cs. Tóth, J. Daniels, D. E. Mittelberger, S. S. Bulanov, J.-L. Vay, C. G. R. Geddes, and E. Esarey

Phys. Rev. Lett. 113, 245002 (2014)

Published December 8, 2014

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