Network defense plan against major incidents

Power grids enable all means of production to operate in parallel and supply all consumers simultaneously. They are highly efficient systems, offering considerable savings and high levels of quality. However, like all complex systems, they can be fragile if a number of precautions are not taken.

To guarantee quality of service to their customers, power companies have developed planning and operating rules to ensure that the power grid is able to cope at all times with current contingencies, such as the loss of one or more transmission or generation facilities. These rules are based on an acceptable "cost/risk of power outage" compromise.

Since covering all possible contingencies would be prohibitively expensive, these rules alone do not guarantee that the power grid is completely protected against major incidents. These incidents, which affect a large number of consumers on a regional or national scale, are due to a combination of common phenomena and aggravating factors, such as the failure of protection or control devices. These situations, fortunately rare, go far beyond those taken into account when developing planning or operating rules. However, they did occur, for example, in France in 1978 and 1987, in Japan in 1987 and, more recently, on the West Coast of the USA in July and August 1996.

The consequences of such incidents are far-reaching, in terms of the economy (electricity is one of the cornerstones of the functioning of the economy), sociology (modern societies are very sensitive to power cuts), and safety (sensitive processes, private customers such as hospitals, etc.). These consequences are, of course, strongly linked to the size of the area without power, and to the time it takes to restore power to that area.

In practice, to deal with major incidents and limit their consequences, power companies adopt curative measures and install specific PLCs, which constitute the power system's defense plan. By limiting the spread of these incidents and facilitating the rapid reconnection of consumers in de-energized areas, defense plans are an essential economic complement to standard planning and operating rules.