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Rolling blackout: Wikis


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A rolling blackout, also referred to as load shedding, is an intentionally-engineered electrical power outage. Rolling blackouts are a last resort measure used by an electric utility company in order to avoid a total blackout of the power system. They are usually in response to a situation where the demand for electricity exceeds the power supply capability of the network. Rolling blackouts may be localised to a specific part of the electricity network or may be more widespread and affect entire countries and continents. Rolling blackouts generally result from two causes: insufficient generation capacity or inadequate transmission infrastructure to deliver sufficient power to the area where it is needed.

In many African and South Asian countries (e.g. Bangladesh, India, Yemen, Nepal, Pakistan, Cameroon, Democratic Republic of the Congo, Nigeria and Zimbabwe) rolling blackouts are a staple of daily life. Sometimes, these blackouts are scheduled at fixed times of the day and week, allowing people to work around the known interruption times. In most other cases, the blackouts may happen without any advance notice, typically when the transmission frequency falls below the 'safe' limit.



Electrical generation and transmission systems may not always meet peak demand requirements— the greatest amount of electricity required by all utility customers within a given region. In the effort to reduce the electric demand on power grids at critical periods, researchers developed a ballast prototype that quickly and reliably sheds the electric load within a building’s lighting system.[1][2] A load-shedding ballast is an instant-start ballast with bi-level dimming and a built-in power line carrier (PLC) signal receiver for automated dimming response.

By dimming lighting via an electronic signal, the ballast reduces the current supplied to the lamps. A signal injector on the building’s lighting circuits controls the ballasts, eliminating the need for extra wiring.[3] The ballasts respond to a signal sent by the utility or the customer’s energy management system, reducing power to the lighting by one third. Field studies showed that building owners could dim the lights by as much as 40% for brief periods of time without upsetting 70% of the building’s occupants or hindering productivity. Ninety percent of building occupants accepted the reduction in light levels when they were told that it was being done to conserve energy.[4]

The new ballast system works on individual light fixtures, not on the main power grid. The system is recommended for new construction and remodeling and promises good return on investment in energy savings. In U.S.-based markets, the system has a three-year or less payback period for new construction.[5] The ballast’s use has the potential to reduce U.S. peak electric demand by 20,000 megawatts. If used widely, it has the potential to help avoid blackouts.

OSRAM SYLVANIA modified the load-shedding system design described above and incorporated it into the QUICKTRONIC (R) PowerSHED(TM) High Efficiency Demand Response Ballast. Additional work is being done to modify additional lamp types to provide for load-shedding, such as high-intensity discharge lamps. [6]


In 2004-05, electricity demand outstripped supply by 7-11%.[7] Due to a chronic shortage of electricity, power-cuts are common throughout India, adversely affecting the country's potential for economic growth.[8][9] Even in the nation's capital of New Delhi, rolling blackouts are common, especially during the hot summer season when demand far outstrips supply. Rural areas are the most severely affected; it is common for the 44% of rural households having access to electricity to lose power for more than 12 hours each day [10].


Due to the weak infrastructure of power distribution combined with high energy use for air conditioning and emerging technology, major cities in Iran are subject to rolling blackouts. They generally occur from 10:00 AM until 1:00 PM and/or late at night so that the citizens are not awake during the blackout. Occasional blackouts began in 2006, and their frequency has increased to 2 per day in the most heavily populated cities such as Tehran.

Republic of Ireland

On several occasions in the 1970s and 1980s trade union strikes in Ireland's power utility, the Electricity Supply Board (ESB), led to rolling blackouts. However, rolling blackouts have not occurred for this reason since 1991. For such eventualities, the ESB have a zone rota system in place. The country is divided into regions which in turn are subdivided into zones, referred to by the letter codes A, B, C, X, Y, and Z. During periods when blackouts may occur, advertisements are placed in the national newspapers informing customers which region and zone they are in, and at what times of the day they have a high, moderate or low risk of supply interruption. (Customers fortunate enough to live close to a hospital may find they are on a "priority line" and don't lose power at all). The authorities appeal to the public to conserve electricity (especially during hours of peak demand); however, if and when electricity demand exceeds available supply, supply is cut in some or all of the "high risk" zones. If there is still a shortfall once all the high risk zones have had power cut, then the "moderate risk" zones start experiencing power cuts. The level of risk in each zone changes every three hours moving from "Low" to "Moderate" to "High" and back to "Low".


Kathmandu, faced with an influx of rural migrants and rising energy demands, faces load-shedding even during the monsoon when the rains fill the water reservoirs where electricity is generated. During the dry winter months, electricity was cut up to sixteen hours per day, leading to disruption of the economy. In the rest of the country, electrification has occurred patchily, although in some small villages a small hydropower project set up locally may function more reliably than the power supply of the capital city.

2008 State of Energy Emergency

The Maoist-led government has declared a State of Energy Emergency as the ever-increasing demand of electricity and the short supply of it has resulted in a severe energy crisis in the country. This shortage has been credited to the decreasing level of water in reservoirs of several hydro power plants of the country. But now the authority centre have the power cut only for four hours a day but also facing lots of problems, especially it is faced by the students and the development workers.

South Africa

The history and causes of rolling blackouts in South Africa are multiple. In South Africa the major producer and distributor of electricity is Eskom, which provides over 95% of the country's energy usage. During the 1980s Eskom mothballed three of their coal-fired power stations, as there was an excess of generation capacity at the time. With the demise of Apartheid in the 1990s came massive investment and economic growth. At the same time the government tried to deregulate the electricity supply industry by inviting the private sector to build new power stations to meet the rapidly growing demand for electricity. Eskom was at the time prevented from building new power stations (including de-mothballing the three existing power stations) or from strengthening the transmission network. The transmission network is especially important in delivering power from Mpumalanga, where the majority of the power stations are located, to other parts of the country such as KwaZulu-Natal and the Western Cape. With no bidders coming forward to construct new power stations, there was effectively no investment into new generation plants during the early 1990s, which eventually led to the shortage of capacity that was experienced in the 2000s.

In 1998, the Department of Minerals and Energy released a detailed energy review in which it explicitly warned that unless "timely steps were taken to ensure that demand does not exceed available supply capacity", generating capacity would reach its limit by 2007.[11]


Blackouts in Western and Northern Cape 2005—2006

The energy consumed by the Western and Northern Cape are only partially supplied by Koeberg nuclear power station, with the balance of the energy supplied by the coal-fired power stations in Mpumalanga via the transmission network. In December 2005, a bolt left in Koeberg Unit 1 reactor after maintenance caused extensive damage to the rotor, resulting in it tripping out. As a result, there was insufficient power to supply the Cape, with the transmission network only partially able to supply the electricity demand. As a result rolling blackouts were implemented across the two provinces.

The blackouts and the accompanying brouhaha in the media resulted in Eskom and the government announcing a number of plans for new power stations, and Eskom started returning mothballed power stations to service as well as expediting plans to build new gas-fired power stations to support the Western Cape supply.

Country-wide blackouts 2007—2008

With the freeze on any new developments being placed on Eskom during the early 1990s, the country was faced with a situation where for the next few years the electricity demand kept rising, without any new power stations being built to keep up the necessary supply. By October 2007 the situation had deteriorated to such an extent that Eskom implemented rolling blackouts throughout the country. Blackouts occurred in most suburbs throughout the country for a period of two hours at a time.

The situation came to a head on 24 January 2008 when the national grid was brought to near collapse. Multiple trips at a number of different power stations rapidly reduced the available supply, resulting in Eskom declaring force majeure[12] and instructing its largest industrial customers (mainly gold and platinum mining companies) to shut down their operations and reduce consumption to "minimal levels", just sufficient to evacuate workers that were still in the mines.[13]

In January 2008, with no short- or medium-term relief available to ease the power shortages, Eskom warned the public that the country's electricity demand would exceed the supply until 2013 (when the first new power stations would be brought online).


In January 2008 Tajikistan faced its coldest winter in 50 years, and the country's energy grid began to fail. By February 2008 Tajikstan's energy grid was near collapse and there were blackouts in most of the country. Hospitals throughout the country were on limited electricity use, and nurses and doctors were forced to keep newborn babies warm with hot water bottles. There were reports of newborns freezing to death. The UN reported that with so much energy required to keep warm there was a danger of people starving to death.

United Kingdom

The Three-Day Week of January to March 1974, introduced to limit electricity consumption, and thus conserve coal supplies which were severely reduced due to industrial action, meant that non-essential commercial users were only allowed to consume electricity for three days each week. Home electricity supplies were also limited in some areas.

United States


In April 2006, parts of Texas experienced rolling blackouts due to excessive air conditioner use because of unexpectedly high temperatures. The longest power outage lasted for a period of five hours, affecting areas in the Middle to the South of Texas.[citation needed] The Texas power system runs on a system similar to the one in California.


Though the term did not enter popular use in the U.S. until the California electricity crisis of the early 2000s, outages had indeed occurred previously. The outages were almost always triggered by unusually hot temperatures during the summer, which causes a surge in demand due to heavy use of air conditioning. However, in 2004, taped conversations of Enron traders became public showing that traders were purposely manipulating the supply of electricity, in order to raise energy prices.

On December 13, 2003, shortly before leaving office, Governor Gray Davis officially brought the energy crisis to an end by issuing a proclamation ending the state of emergency he declared on January 17, 2001. The state of emergency allowed the state to buy electricity for the financially strapped utility companies. The emergency authority allowed Davis to order the California Energy Commission to streamline the application process for new power plants. During that time, California issued licenses to 38 new power plants, amounting to 14,365 megawatts of electricity production when completed.

Rolling blackouts were again imposed in late August 2005 in Southern California due to the loss of a key transmission line; the transmission line shut itself off because of a faulty sensor.

Most of California is divided into 14 power grids, each containing approximately 7% of electricity customers in the state, creating a total of 98%. The remaining 2% are placed on a separate grid, where users such as hospitals and police stations are exempt from ever having their power deliberately cut off.

In a Stage 1 emergency only a general call for voluntary conservation is issued, while a Stage 2 emergency results in power being temporarily cut off to certain large users, primarily industrial concerns, who have agreed to this arrangement in exchange for lower rates. When a Stage 3 power emergency is declared, electricity to one of the grids is shut off for a fixed period of time, which can range from 60 minutes to 2½ hours. If after this period of time the Stage 3 emergency still exists, power is restored to this grid but then the next grid in the sequence is blacked out, and so on, until the situation is stabilized — the blackout thus "rolls" from one grid to the next.

In California, each customer's electric bill includes the number of the power grid (from 1 to 14) that customer belongs to; this gives customers at least some advance notice of when their electricity might be turned off in the event of a Stage 3 emergency. The grids are set up in such a manner as to ensure that a large percentage of customers in the same neighborhood would not be blacked out concurrently, which could invite looting and other related problems. Normal electricity customers can fall within the areas reserved for emergency use (if they are near a hospital or other critical infrastructure), in which case their electric bill will indicate a power grid of 99 and they will not be affected by rolling blackouts.


In many East Coast states (such as New York State and New Jersey), "brownouts" rather than rolling blackouts are implemented during power emergencies.[citation needed] In this scenario, instead of the power being cut off altogether to a certain percentage of customers, the voltage is reduced by a certain percentage to all customers — the resulting dimming of electric lights being the origin of the term "brownout." Brownouts can cause significant damage to unprotected electronic equipment, but usually have no effect (other than reduced performance) on incandescent lights or some types of motors.


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