System security is the ability to withstand sudden short-term disturbances such as operational transmission failures, unanticipated losses of generating units, changes in load conditions and other contingencies, as well as human errors. System adequacy comprises both the ability of generating the power required by customers (referred to as generating adequacy) and that of transporting the energy to the actual customer load points (transmitting adequacy). The crucial burden on a local electricity generation system is to cope with variation of demand and to meet peak demand (often referred to as “peak load”).