[5] The software provides answers to the "what if" scenarios in the form of "alarms": "Loss of component X will result in overload of Y by Z%".
Due to the rapid change of the state of a power system the run of the application shall complete in minutes (up to 30[6]) for the results to be useful.
The system that satisfies this requirement is described as meeting the N-1 contingency criterion (N designates the number of pieces of equipment).
The N-2 and N-3 contingency refers to planning for a simultaneous loss of, respectively, 2 or 3 major units; this is sometimes done for the critical area (e.g.
At the distribution level, however, the planners frequently allow a more relaxed interpretation: a single failure should ensure uninterrupted delivery of power to almost all the customers at least at the "emergency level" (Range B of the ANSI C84.1[9]), but a small section of the network that contains the original fault might require manual switching with a service interruption for about an hour.