Power outage

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

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 momentary (a few seconds) loss of power typically caused by a temporary fault on a power line. Power is automatically restored once the fault is cleared.
• A brownout or sag 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 refers to 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 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 fuses in households.

      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 prevent 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 an 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 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.

How to avoid outages?

         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.

Cities with more blackouts:

       Power outage are very frequent

•  Burma (As in Kamayut, Yangon, the rate for blackout is approximately 3221h/yr &Mandalayapproximately 3172h/yr.),

       blackout is also frequent                      

•   Malaysia, Philippines, Zambia, Laos, Hungary, Turkey, Mexico, Indonesia and People's  
•   Republic of China. In Petaling Jaya in Malaysia rate for 2007 is 936h/yr, 
•   Rompin in Pahang, Malaysia is 377h/yr.
•   Budapest in Hungary is approximately 529h per year