Power Outage

A power outage 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.

A power outage may be referred to as a blackout if power is lost completely, or as a '''brownout''' if some power supply is retained, but the voltage level is below the minimum level specified for the system. Some brownouts, called '''voltage reductions''', are made intentionally to prevent a full power outage.

Power failures are particularly troublesome for Hospital s, since many 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 are left unnoticed by most citizens of moderate means, as maintaining an Uninterruptible Power Supply is often not considered an essential facility of a home.

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.

PROTECTING THE POWER SYSTEM FROM OUTAGES

In power supply networks, the power generation and the demand must be closely matched 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 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 meant to be 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 of 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.

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.

See Also: Uninterruptible power supply

BLACKOUT UNAVOIDABILLITY AND ELECTRIC SUSTAINABILITY

It has recently been argued on the basis of historical datahttp://www.computer.org/proceedings/hicss/1435/volume2/14350063abs.htm and computer modellinghttp://ffden-2.phys.uaf.edu/HICSS2002-paper2.pdf that Power Grid s are Self-organized Critical Systems . These systems exhibit unavoidablehttp://eceserv0.ece.wisc.edu/~dobson/PAPERS/carrerasHICSS00.pdf 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 oneshttp://eetd.lbl.gov/certs/pdf/Dobson_4.pdf. This has immediate policy implications. 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

...the 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!

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.

First and perhaps most striking is the intrinsic unavoidability of cascading events in such a system when driven near its operational limits.

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Power Outage