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A power outage (also called a power cut, a power out, a power blackout, a power failure, a power loss, or a blackout) is the loss of the
electrical power Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Electric power is usually produced by electric generators, but can also be suppli ...
network supply to an
end user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ultimately use a product. The end user stands in contrast to users who support or maintain the product, such as sysops, system administrators ...
. There are many causes of power failures in an electricity network. Examples of these causes include faults at
power stationPower Station or The Power Station may refer to: * Power station, a facility for the generation of electricity Music * The Power Station (band), a 1980s supergroup ** ''The Power Station'' (album), a 1985 album by The Power Station * Power Station ...
s, damage to
electric transmission lines Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a ''transmission network''. Thi ...
, or other parts of the
distributionDistribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a variabl ...
system, a
short circuit A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. ...
,
cascading failure An animation demonstrating how a single failure may result in other failures throughout a network. A cascading failure is a process in a system of interconnected parts in which the failure of one or few parts can trigger the failure of other parts a ...
,
fuse Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protect ...
or
circuit breaker A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a faul ...
operation. Power failures are particularly critical at sites where the environment and public safety are at risk. Institutions such as
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s,
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plants, and mines 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 Telecommunication is the transmission of information by various types of technologies over wire, radio, optical or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasi ...
, are also required to have emergency power. The
battery room A battery room is a room that houses batteries for backup or uninterruptible power systems. The rooms are found in telecommunication central offices, and provide standby power for computing equipment in datacenters. Batteries provide direct curren ...
of a telephone exchange usually has arrays of Lead–acid battery, lead–acid batteries for backup and also a socket for connecting a generator during extended periods of outage.

# Types of power outage

Power outages are categorized into three different phenomena, relating to the duration and effect of the outage: * A transient fault is a loss of power typically caused by a fault on a power line. Power is automatically restored once the fault is cleared. * A brownout (electricity), 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 stationPower Station or The Power Station may refer to: * Power station, a facility for the generation of electricity Music * The Power Station (band), a 1980s supergroup ** ''The Power Station'' (album), a 1985 album by The Power Station * Power Station ...
s 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. Rolling blackouts occur when demand for electricity exceeds supply, and allow some customers to receive power at the required voltage at the expense of other customers who get no power at all. They are a common occurrence in developing countries, and may be scheduled in advance or occur without warning. They have also occurred in developed countries, for example in the California electricity crisis of 2000–2001, when government deregulation destabilized the wholesale electricity market. Blackouts are also used as a public safety measure, such as to prevent a gas leak from catching fire (for example, power was cut to several towns in response to the Merrimack Valley gas explosions), or to prevent wildfires around poorly maintained transmission lines (such as during the 2019 California power shutoffs).

# Protecting the power system from outages

In grid (electricity), 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 Fuse (electrical), 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. In that case, the short-term economic benefit of keeping the individual customer happy increases the likelihood of large-scale blackouts. The United States Senate Committee on Energy and Natural Resources, Senate Committee on Energy and Natural Resources held a hearing in October 2018 to examine "black start", the process of restoring electricity after a system-wide power loss. The hearing's purpose was for Congress to learn about what the backup plans are in the electric utility industry in the case that the electric grid is damaged. Threats to the electrical grid include cyberattacks, solar storms, and severe weather, among others. For example, the "Northeast blackout of 2003, Northeast Blackout of 2003" was caused when overgrown trees touched high-voltage power lines. Around 55 million people in the U.S. and Canada lost power, and restoring it cost around \$6 billion.

# Protecting computer systems from power outages

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

Restoring power after a wide-area outage can be difficult, as power stations need to be brought back online. 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 Bootstrapping#Electric power grid, bootstrap the power grid into operation. The means of doing so will depend greatly on local circumstances and operational policies, but typically Electric power transmission, 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

## OPA model

In 2002, researchers at Oak Ridge National Laboratory (ORNL), Power System Engineering Research Center of the University of Wisconsin (PSerc), and the University of Alaska Fairbanks proposed a mathematical model for the behavior of electrical distribution systems. 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. The OPA model was quantitatively compared with a complex networks model of a cascading failure – Crucitti–Latora–Marchiori (CLM) model, showing that both models exhibit similar phase transitions in the average network damage (load shed/demand in OPA, path damage in CLM), with respect to transmission capacity.

## Mitigation of power outage frequency

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: * 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. A complex network-based model to control large cascading failures (blackouts) ''using local information only'' was proposed by A. E. Motter. In 2015, one of the solutions proposed to reduce the impact of power outage was introduced by M.S. Saleh.

# Key performance indicators

Utilities are measured on three specific performance measures: * SAIDI, System Average Interruption Duration Index, measured in minutes * CAIDI, Customer Average Interruption Duration Index, measured in minutes * CAIFI, Customer Average Interruption Frequency Index

* 2019 Venezuelan blackouts * 2019 Java blackout * 2012 India blackouts * 2003 Italy blackout * 2011 Southwest blackout * 2019 California power shutoffs * February 13–17, 2021 North American winter storm * ''Brittle Power'' * Coronal mass ejection * Critical infrastructure protection * Cyberattack * Dumsor * Electromagnetic pulse (EMP) * Energy conservation * Internet outage * List of major power outages * List of energy storage projects * New York City blackout of 1977 * Northeast blackout of 1965 * Northeast blackout of 2003 * Outage management system * Proactive cyber defence * Renewable energy * Rolling blackout * Self-organized criticality control * Smart grid * Uninterruptible power supply