Method of Eliminating Transmission Line Overload in Electricity Spot Market

China is promoting inter-provincial electricity spot market construction to optimally allocate power resources in a broader scope. At present, China's electricity spot market first executes inter-provincial transactions to determine tie-line power and then executes intra-provincial transactions. However, in AC interconnected power grid, when merely taking the tie-line power as power injection of border nodes, the results of intra-provincial market clearing may engender transmission line overload. This paper first established electricity spot market clearing models, then analyzed the causation for transmission line overload and proposed the concept of critical border nodes. Ultimately the method based on phase angle monitor is proposed to eliminate transmission line overload. A modified IEEE-39 system is tested to prove the effectiveness of the proposed method.