With the ever-increasing large-scale HVDC transmission systems

the coupling problem between AC and DC systems is outstanding

which increases the risk of cascading failures. An event chain search model for fast contingency screening in the AC/DC hybrid power system is proposed

which includes the AC outage search model and the judgment module of the occurrence of DC faults. In the AC outage search model

the influence on the operation of DC systems and structural importance of lines is considered and a novel search strategy in the AC grid which is based on outage risk index after preliminary screening by outage probability value is put forward. In the judgment module of the occurrence of DC faults

the short-circuit faults and the overload trips in the AC grid are set apart considering the interactions with DC systems. In addition

a method of correlation analysis for cascading failures based on the modified Apriori algorithm considering the order of items and the weight of transaction is proposed to select the strong association rules endangering system security. Finally

simulation results demonstrate that the event chain search model can search the fault paths effectively in which DC systems are out of operation and reduce the omission of high-risk chains

and the method of correlation analysis can identify the strong association rules that endanger system security.