This paper addresses the condition monitoring and diagnostics of twelve-pulse load commutated inverter drive systems, focusing on the occurrence of faults of the open-switch type in the power converters. The results presented are based on different monitoring techniques, namely, mechanical vibrations, axial leakage flux and temperature measurements. The goal of this study is to analyse the variations imposed by a fault in some critical parameters, related to the operating conditions and electromechanical limits of the drive, in order to introduce fault-tolerant characteristics and, therefore, increasing its survivability.