Thereinto,the so-called dispatching economy has been considered by power system expected operating cost,which has also included the security corrective costs of unit ramping and load interruption at the contingency state.

This paper proposes methods improve on contingency ranking and security corrective.

A method for active power security correction in power market based on genetic algorithm was put forward which means an appropriate regulation of the active power output of the generator to alleviate active power overload of transmission line with the least increase of market purchase cost.