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.

Power failures are particularly damaging for hospitals, since many life-critical medical devices and tasks require power. For this reason hospitals, just like many enterprises, have emergency power generators which are typically powered by Diesel fuel and configured to start automatically, as soon as a power failure occurs.

Other life-critical systems such as telecommunications are also required to have emergency power.

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 fuses 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 network.

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 likelyhood of small outages only increases the likelyhood of larger ones. In that case, the short-term economic benefit of keeping the individual customer happy increses the likelyhood 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

Blackouts are unavoidable ? and electric sustainability

It has recently been argued on the basis of historical data 2002a and computer modelling 2002b that power grids are self-organized critical systems. These systems exhibit unavoidable 2000 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 2003. This has immediate policy implications 2002a. 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 2003

...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! 2002a

[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. 2002b

First and perhaps most striking is the intrinsic unavoidability of cascading events in such a system when driven near its operational limits. 2000

See also

• List of power outages
• renewable energy.

External links

• The Blackout History Project documenting two New York City blackouts
• about restoring power
• A. E. Motter and Y.-C. Lai, Cascade-based attacks on complex networks, Physical Review E (Rapid Communications) 66, 065102 (2002).
• Nature: Blackouts inherent in power grid