[[Image:Crossed wires.JPG|thumb|right|300px|Tree limbs create a short circuit in electrical lines during a storm.]]
A '''power outage''' (Also ''power cut'', ''power failure'' or ''power loss'') is the loss of the [[electricity supply]] to an area.

The reasons for a power failure can for instance be a defect in a [[power station]], damage to a power line or other part of the distribution system, a [[short circuit]], or the overloading of electricity mains. While the developed countries enjoy a highly uninterrupted supply of electric power all the time, many developing countries have acute power shortage as compared to the demand. Countries such as [[Pakistan]] have several hours of daily power-cuts in almost all cities and villages except the metropolitan cities and the state capitals. Wealthier people in these countries may use a power-inverter or a diesel-run [[electric generator]] at their homes during the power-cut.

A power outage may be referred to as a [[blackout]] if power is lost completely, or as a [[brownout]] if the voltage level is below the normal minimum level specified for the system, or sometimes referred to as a short circuit when the loss of power occurs over a short time (usually [[second]]s).  Systems supplied with [[three-phase electric power]] also suffer brownouts if one or more phases are absent, at reduced voltage, or incorrectly phased.  Such malfunctions are particularly damaging to [[electric motor]]s. Some brownouts, called voltage reductions, are made intentionally to prevent a full power outage. 'Load shedding' is a common term for a controlled way of rotating available generation capacity between various districts or customers, thus avoiding total wide area blackouts.

Power failures are particularly critical for [[hospital]]s, since many [[life-critical system|life-critical]] medical devices and tasks require power. For this reason hospitals, just like many enterprises (notably [[colocation]] facilities and other [[datacenter]]s), have emergency power generators which are typically powered by diesel fuel and configured to start automatically, as soon as a power failure occurs. In most [[third world]] countries, power cuts go unnoticed by most citizens of upscale means, as maintaining an [[uninterruptible power supply]] is often considered an essential facility of a home.

Power outage may also be the cause of [[sanitary sewer overflow]], a condition of discharging raw sewage into the environment.  Other life-critical systems such as [[telecommunications]] are also required to have emergency power. Telephone exchange rooms usually have arrays of [[lead-acid batteries]] for backup and also a socket for connecting a [[diesel]] generator during extended periods of outage.

Power outages may also be caused by [[terrorism]] (attacking power plants or [[electricity pylon]]s) in developing countries. The [[Shining Path]] movement was the first to copy this tactic from [[Mao Zedong]].

== Protecting the power system from outages ==
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. In order to prevent this, parts of the system will automatically disconnect themselves from the rest of the system, or shut themselves down to avoid damage. This is analogous to the role of relays and [[Fuse (electrical)|fuse]]s in households.

Under certain conditions, a network component shutting down can cause current fluctuations in neighboring segments of the network, though this is unlikely, 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 the 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, some observers 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. It has been claimed that reducing the likelihood of small outages only increases the likelihood of larger ones. In that case, the short-term economic benefit of keeping the individual customer happy increases the likelihood of large-scale blackouts.

== Power Analytics ==
[[Power Analytics]] is the term used to describe the management of electrical power distribution, consumption, and preventative maintenance throughout a large organization’s facilities, particularly organizations with high electrical power requirements.  For such facilities, electrical power problems – including the worst-case scenario, a full power outage – could have a devastating serious impact. Additionally, it could jeopardize the health and safety of individuals within the facility or in the surrounding community.

Power Analytics use complex mathematical algorithms to detect variations within an organization’s power infrastructure (measurements such as voltage, current, power factor, etc.). Such variations could be early indications of longer-term power problems; when a Power Analytics system detects such variations, it will begin to diagnose the source of the variation, surrounding components, and then the complete electrical power infrastructure. Such systems will – after fully assessing the location and potential magnitude of the problem – predict when and where the potential problem will occur, as well as recommend the preventative maintenance required preempting the problem from occurring.

== Restoring power after a wide-area outage ==
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 absence of grid power, a so-called [[black start]] needs to be performed to [[bootstrap]] the power grid into operation.

{{seealso|Uninterruptible power supply}}

== Blackout unavoidabillity and electric sustainability ==
It has recently been argued on the basis of historical data<ref name="ref2002a">http://www.computer.org/proceedings/hicss/1435/volume2/14350063abs.htm</ref> and computer modelling<ref name="ref2002b">http://ffden-2.phys.uaf.edu/HICSS2002-paper2.pdf</ref> that [[power grid]]s are [[self-organized criticality|self-organized critical systems]]. These systems exhibit unavoidable<ref name="ref2000">http://eceserv0.ece.wisc.edu/~dobson/PAPERS/carrerasHICSS00.pdf</ref> disturbances of all sizes, up to the size of the entire system, and attempts to reduce the probability of small disturbances only increase the probability of large ones<ref name="ref2003">http://eetd.lbl.gov/certs/pdf/Dobson_4.pdf</ref>. This has immediate policy implications<ref name="ref2002a"/>. The following are the relevant quotations from the sources cited:

:''As expected from studies of general self-organised critical systems, ... apparently sensible efforts to reduce the risk of smaller blackouts can sometimes increase the risk of large blackouts'' <ref name="ref2003"/>

:''...the [[North American Electric Reliability Council|NERC]] blackout data suggests that the North American power system has been operating near criticality. ...It would be better to analyze this tradeoff between catastrophic blackout risk and loading instead of just waiting for the effects to manifest themselves in the North American power system!'' <ref name="ref2002a"/>

:''[The models'] PDF of the blackouts size has the same power dependence that have been found from the analysis of NERC data for the North American power grid over a period of 15 years.'' <ref name="ref2002b"/>

:''First and perhaps most striking is the intrinsic unavoidability of cascading events in such a system when driven near its operational limits.'' <ref name="ref2000"/>

==See also==
* [[List of power outages]]
* [[Renewable energy]]
* [[Rolling blackout]]

==References==
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==External links==
{{Wikinews|Category:Disasters and accidents}}
*[http://blackout.gmu.edu/home.html The Blackout History Project] documents two New York City blackouts
*[http://www.windows.ucar.edu/spaceweather/cold_start.html 3 Major Problems in Restoring Power After a Black Out] Space Weather
*A. E. Motter and Y.-C. Lai, [http://chaos1.la.asu.edu/~yclai/papers/PRE_02_ML_3.pdf ''Cascade-based attacks on complex networks,''] Physical Review E (Rapid Communications) 66, 065102 (2002)
* [http://www.ontariotenants.ca/electricity/hydro-news.phtml Ontario Electricity articles]
* [http://www.ontariotenants.ca/apartment_living/blackout.phtml Electricity Power Blackout and Outage tips]
* [http://www.timboucher.com/journal/2005/06/03/blackout-2003/ First-Hand Account of NYC's 2003 Blackout]
* [http://www.siemens.com/index.jsp?sdc_p=cflo1350919psu12  Siemens AG - Blackout Prevention]
* [http://en.wikinews.org/wiki/Europe_suffers_widespread_power_cuts Europe suffers widespread power cuts].

[[Category:Blackouts| ]]
[[Category:Failure]]

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