Electric power system breakdown is a rather rare event. However, when it occurs the influence on society and the costs are tremendous. The electric power system is the most complex, widespread, and powerful interconnected process ever designed and constructed by humankind. Power systems normally cover many countries in synchronous operation, which means that changes of the operational conditions in one part of the system affect those in the rest of the system.

In normal stable operation these changes are small, coordinated, and well planned for, and do not affect the stability or the integrity of the system. Power systems will always be exposed to faults, such as earth faults and short circuits, caused by lightning strokes or insulation breakdown. Ever since the beginning of the electrification era, protection has been used to rapidly disconnect a power system element, such as a line, transformer, or generator, if it is faulted or overloaded, in order to save the element from total destruction and to continue the power supply to the healthy part of the system. However, power systems may, slowly or more rapidly, slide towards instability. Such a transition, from stable operational conditions, can be triggered by a very severe disturbance (such as the loss of a number of lines or of a whole substation) in a stressed operational situation (high load level and large power transfers). It could also be a result of a very rapid load growth, where the corresponding increase in generation cannot be achieved.

To preserve the integrity of the power system and avoid a widespread system breakdown, wide-area protection systems are now being introduced. Other names of systems aimed at taking actions to preserve the power system operation, even though no specific element is overloaded or faulted, are remedial action schemes (RAS); system protection schemes (SPS); and wide-area monitoring, protection, and control systems (WAMPAC).