In order to effectively coordinate the security and economy of the operation of power systems

and rationally assess the optimum operation power of transmission sections

the concept of economical transmission power of transmission sections based on quantitative analysis of security and stability risk assessment of power systems is proposed. The economical transmission power is defined as the section transmission power when the difference of transmission economic benefits and power system instability risk gets the maximum value

and the emergency control cost under unstable contingency is seen as the instability risk of the power system. A practical method of economical transmission power calculation is proposed

and suggestions for power system dispatchers application are given. Simulation results of an actual large-grid test system show that better economic performance can be attained on the basis of the controllable power system risk provided the transmission sections operate at the economical transmission power.