The function of static state security analysis for the traditional energy management system (EMS) is enhanced

and a static state security early warning and preventive control subsystem is designed and implemented. The subsystem can evaluate power system operation’s security level and identify insecure cases in real time. Further more

countermeasures for the insecure cases are also given. The problem of power flow unsolvability due to heavy load for certain contingencies

which represent the most severe cases

is investigated. Based on the minimum mismatch function and successive linear programming method

a practical algorithm is developed to restore power flow from unsolvability. A digital simulation on an actual provincial power system is made to demonstrate feasibility and applicability of the method proposed. The method proposed has been embedded in an early warning and security countermeasure system running in a control center of a provincial power grid.