Power cut

A power cut is the suspension of the distribution of the Electric current in a given area. This can come from a defect in a Powerplant, equipment of distribution damaged (for example, by a storm of Neige or rain verglaçante), a Court-circuit or an overload of the system.

The term Blackout is also used when the breakdown relates to a great number of customers.

Great Incidents (large general breakdowns)

One often uses in this case the Anglicisme Blackout .

The Memorandum of the safety of the electric system , published by RTE on its official site, presents the modes of degradation of the safety of the electric system leading to the blackouts, as well as a panorama of the great incidents which have occurred throughout the world.

The annual Balance sheet safety of the safety of the electric system French , also available on the site of RTE for each year since 2001, comprises a chapter presenting the large breakdowns which have occurred throughout the world during the year.

American breakdown of November 9th, 1965

The initiating cause of this great incident is the inopportune disjunction of a line 230 Kv forwarding the electricity of the power station of Niagara Falls to Ontario. Following the carryforward of load, it follows the setting not under tension by cascade many other lines as well as disjunction of groups of production. The network separates in several sub-networks, but none is viable. Almost the totality of the North-East of the United States and the South of Ontario are not under tension, plunging in the darkness 30 million people. It will be necessary more than thirteen hours to take again the totality of the service.

American breakdown of July 13rd, 1977

New York was touched by a power failure which started plunderings and riots involving the arrest of 4000 people. This great incident is due to a storm, whose successive loves at first sight on lines of transport cause the loss of these lines and groups of production. For lack of unballasting carried out sufficiently quickly, of new disjunctions occur in cascade. The whole of New York cut east, is approximately 6 GW. One will completely need about fifteen hours for réalimenter New York.

French breakdown of December 19th, 1978

General breakdown, on December 19th, 1978, due to a cascade of disjunctions of lines with very high voltage by carryforwards of load, following the entry in initial overload of a line 400 Kv in the east of France, at the time of a situation of strong imports of electricity of Germany towards France.

Collapse of tension in the west of France on January 12th, 1987

By one day particularly cold, three groups of production of a power station close to Nantes trip in less than one hour for independent reasons. The last group of the power station ends up also taking down. It follows an abrupt degradation of the regional plan of tension, which by repercussion causes new unhookings in several power stations of the west of France. Thanks to the sending of orders of unballasting, the tension is stabilized in the west of France, but on a very low level near to 300 Kv, before the action of the dispatchers leads to the re-establishment of the situation.

Collapse of tension in Japan on July 23rd, 1987

This great incident occurs at the time of temperatures unusually strong at the beginning of afternoon, which cause a massive use of air-conditioning by the Japanese, whereas the electricity demand beat already the records in the morning. It follows a fall of tension, then an instability of tension, which leads to the disjunction of the three powerplants feeding the area of Tokyo. Three million customers is cut.

Storm of glaze of 1998 of the American North-East

The Tempête of glaze of 1998 is a storm of Verglas which took place in January 1998 in the east of the Canada, the New England and the north of the state of New York. It because of the power cuts and important damage to the trees in all this area.

American breakdown of August 2003

An immense power failure seriously touched the states and provinces of the North-East of North America on August 14th, 2003.

See also: Mégapanne North-American of 2003

Swiss incident Italy of September 28th, 2003

Causes:

Before the power cut does not strike Italy and briefly the south of Switzerland at the first hours of the morning on September 28th, 2003, the lines of North-South transit through Switzerland were very charged.
has 3:01, an important line of transit between north and the south of Europe, the line of the Lukmanier, trips. A load of approximately 110% is deferred on the line of transit of the San Bernardino.
GRTN, the owner of the network would have owed stoper of the pumps, but it did not do it.

Swiss breakdown of June 22nd, 2005 on the railway network

on June 22nd, 2005, all the railway network Suisse is blocked during several hours. From 6 p.m. to the following day at 5 a.m. : 100000 people were blocked in the trains, some during one hour.

Cause: A short-circuit occurred with 17:08 on a line of transport of the CF between Amsteg and Rotkreuz, which led to the setback of several powerplants and caused a chain reaction, announced Thursday, June 23 the CF.
the supply electric current of the network was divided in two sectors, the south being overfed while north missed energy. To 17:45, the whole of the power supply had passed not under tension and 1.500 trains were broken down on the network.

European breakdown of November 2006

November 4th, 2006, a breakdown of great importance touched the network of UCTE, depriving of electricity approximately 10 million customers.

The origin would be the programmed setting out-service of two lines 400kV, to leave the passage to a Navire with Ems, in Germany. The remaining lines would have started to overheat, causing their disconnection. By a " domino" effect; of carryforward of load, many other lines would have taken down, practically involving a scission of the network of UCTE into 2, following a North-South line.

The consequences of this power failure were worsened by the overall behavior of the decentralized production. In the majority of the European countries, this behavior was marked by the randomness of the disconnections and of reconnexions wind power stations.

Western Europe being then in deficit of production, of the unballastings were necessary to avoid a total collapse of the network. Approximately 10% of the customers had to be disconnected.

The whole of the network could be restored in approximately an hour.

Mechanisms leading to the great incidents

The electric systems of the large countries are conceived, built and exploited so that the users of the network do not undergo, in some limiting, the consequences of the most current risks. For example, the rule of the “N-1”, into force on the network UCTE, provides that the Electrical communication must remain viable after the loss of any line or any group. In France, where the reference frame of the safety of the electric system is more demanding, one applies the rule known as “N-k”, with k>1: typically, no collapse of the network must occur, even if 2 groups of production start.

But, as one can see it through the examples of large breakdowns precedents, it can occur of the situations much more complex resulting from multiple, very close incidents in time even simultaneous, sometimes associated with failures with systems with protection, regulations or operators. The experience feedback on the great incidents shows that they are always the consequence of a combination of several risks.

By exceeding the framework of the primary education initial risks (loss of a group of production for example) and their multiple potential combinations, the analysis of the great incidents also shows which if one places oneself on a more synthetic level, the genesis of a great incident often results in one of the four following electromechanical phenomena:

the cascade of overloads of lines of transport and their release;
the collapse of frequency;
the collapse of tension;
the rupture of synchronism enters the groups of production.

When the great incidents are very complex and occur on wide area networks, these four phenomena can follow one another, be superimposed or join; thus, the incident of December 19th, 1978 in France started with phenomenon 1 then accelerated and extended with phenomenon 4; the European incident of November 4th, 2006 started with phenomenon 1 and continued with phenomenon 2.

At the end of the Nineties, certain authors evoked a fifth phenomenon: the appearance of low frequency oscillations enters of the important parts of a very wide electric system; however, if the use of very sophisticated recorders, such as the WAMS (Wide Area Measurement Systems), watch which the electric great systems are indeed sometimes prone to occurrences of low frequency oscillations evil quenched, no great incident still occurred following this phenomenon.

Precautionary measures

Among the precautionary measures implemented by the companies of electricity to avoid the major power cuts, one can quote:

Hiding of the electric lines to decrease the sensitivity of the network to the atmospheric disturbances (the Lightning, Glaze.)
Redondance of the electric lines so that the failure of simple a line does not lead to an undesirable event
Maintien of a reserve of power in the central electric
Interconnexion with the adjoining countries to increase the stability of the network
specific Systèmes of improvement of the stability of the network FACTS
Nécessité that the requirements as regards stability of the stations generating decentralized at the time of which has occurred of variations of the frequency of the synchronous inter-connected network are more constraining, i.e. to approve the wind mills only if they continue to function when the frequency of the network falls and that it is absolutely necessary to support the network instead of disconnecting itself.

Very often, the major breakdowns on a Electrical communication utilize an imbalance between the production and consumption. Principal the means of guarding itself against this phenomenon is to set up plans of unballasting.

Parades

The prevention of the large power failures, which are one of the objects of the reliability of the electric systems, is a complex activity which rests on the implementation of multiple provisions, which must be adapted to the dynamics of the four electromechanical phenomena exposed in the preceding chapter. These provisions must make it possible to prevent, detect and treat the dysfunctions being able to lead to the appearance of the one of these phenomena, and, if the phenomenon occurs despite everything, to control the evolution of it.

A robust design of the prevention of the large breakdowns requires to rest on a rigorous conceptual organization. Provisions of defense of system electric French managed by RTE, whose Club of the Operators of Wide-area networks stresses that they must be regarded as one of the best approaches in the world, rest on the implementation of successive lines of defense, according to the approach known as “in-depth defense”. These provisions relate on the one hand to the material field, on the other hand on the organisational and human field. The lines of defense refer to three different shutters: prevention and preparation, monitoring and the action, and finally parades ultimate.

The prevention and the preparation consist in making so that the dreaded phenomena cannot start, protect themselves from the possible failures from the equipment by the material and functional redundancy, identify the activities at the risk and guarantee them by their setting under quality assurance. The electric system must also be conceived in order to be able to support certain risks, which is necessary since one can never prevent the occurrence of risks completely (the experience feedback is there to show it).

The shutter of the monitoring and the action gathers the actions which make it possible to detect the variations of the sizes (frequency, tension, currents…) who are characteristic of the good performance of the electric system, and to start the suitable actions - manual or automatic - when it is necessary.

The third shutter is the ultimate register. Which are the precautions taken with the two preceding parts, no one network operator is not completely safe from the initialization of a large breakdown. When one arrives at this stage, it is necessary to proceed to exceptional actions to stop the collapse, even if it means having to lose part of the network or consumption, or else one is likely to lose the totality of the network (thus, on November 4th, 2006, the totality of the European network could have been lost if the fall of frequency had been prolonged a few seconds moreover, and only the automatic unballasting frequencemetric saved the situation). These measurements must be extremely fast; this is why the recourse to the human actions is not enough, and it is necessary to be pressed on automatic devices.

Various designs exist in the world as for the design of these automatic devices. They depend in particular on the structure of the electric system concerned, and the resources which can be released. Indeed, the design of automatic devices always has a cost, whereas on the contrary one can never be completely sure that these devices will be effective (on the contrary, they can even be at the origin of unnecessary operations). There is thus a balance to find.

In certain electric systems, one considers that it is too expensive and too complex to be protected, and there is no really installation of devices, except relatively rustic provisions of unballasting. It is admitted whereas the network collapses, and one seeks as fast as possible to give it in service.

In other countries where the structure of the electrical communication is rather simple, one considers that one can protect oneself while seeking to detect by studies upstream (studies of stability in particular) the combinations of risks to be feared (for example the simultaneous loss of such line and such group of production), then one sets up for each dreaded combination an automatism able to detect the occurrence and to undertake a suitable action which one will have identified (in general, it is about action on topology, the production and consumption). In this approach, which is called “event-driven”, one thus sets up a series of specific automats (SPS or Special Protection Designs in the English terminology). Thus, Brazil resorts much to such equipment.

In the more complex electric systems, like the North-American network, or as the European network which is even with a grid, such a design is not appropriate: the identification of the combinations to be feared would be too much complicated, and would require a considerable number of SPS; moreover, taking into account the ceaseless evolutions of the electric context, it would unceasingly be necessary to change the functionalities and the site of this equipment; in addition, there is always a considerable risk that a SPS, conceived theoretically to act on a precise occurrence, activates in an undesirable way in other configurations not envisaged. This is why one prefers to return to the source and to set up devices able to detect the emergence of the electromechanical phenomenon dreaded itself , and to engage actions. Thus, the provisions of defense are conceived in France in order to know to detect the collapse of tension, or the loss of synchronism between zones of the network. This does not exclude to supplement these provisions by a very limited number of SPS.

Corrective measures

References

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