This paper proposes an impact-increment-based hybrid (IIHybrid) reliability assessment approach for power transmission systems. The proposed approach integrates the advantages of the impact-increment-based state enumeration method (IISE) and impact-increment-based Monte Carlo simulation (IIMC) to improve computational efficiency and accuracy. The IISE can efficiently assess the impacts of low-order contingencies. The accuracy is

however

sacrificed as highorder contingencies are usually neglected. The IIMC is more suitable for large-scale contingency spaces compared with IISE

although the calculation process is time-consuming. In this paper

the proposed IIHybrid takes advantage of its strengths while avoiding its shortcomings. The IISE and the IIMC are applied to lower and higher contingency spaces respectively. The high-order contingencies elimination technique proposed in our previous studies is still applicable to the IIHybrid. In addition

efficiency can be controlled by modifying the preset parameters to adapt to various scenarios. Case studies are performed on the IEEE 118-bus test system and PEGASE System. The results show that the proposed approach is more efficient and practicable than traditional methods.