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The behaviors of transient phenomena in HVDC systems, including DC line faults, commutation failures caused by AC faults and missing firing are difficult to be identified automatically by the control systems, while the effective protection control for commutation failures depends on the rapid and correct identification of such faults. This paper proposes a method to identify different causes leading to commutation failures based on the wavelet transform. By using the technique of wavelet multi-resolution analysis (MRA), the transient signals generated by the faults are decomposed into different resolution levels. The features of each fault are extracted. Two auxiliary parameters are defined as the criteria for the identification, based on which four thresholds are set to distinguish different faults. Simulation results indicate that the proposed approach could make a definite identification of commutation failures from DC line faults and normal operations. Furthermore, the discriminations between AC short circuit faults and missing firing faults, which cause commutation failures, also could be obtained.