contingency planning is based on its advantages:
* each of the N elements in the system is analyzed separately, limiting the amount of work to be done and simplifying the failure options (e.g., generator failure, short circuit);
* the process inherently provides a way to deal with the contingency if and when it will happen.

The N-1 contingency planning is typically sufficient for the systems with the usual ratio of peak load to capacity (below 70%). For a system with a substantially higher ratio, the N-1 planning will not deliver