This paper presents a study concerning the behaviour of harmonic filters in a twelve-pulse LCI drive system after the occurrence of an open-switch fault in the line-side power converters. The main objective of this study is to analyse the operation of the filter subjected to the new harmonics developed by the drive under faulty operating conditions, with and without the introduction of compensating modes of operation, developed with the goal of introducing fault-tolerance to these high-power adjustable speed motor drives. To validate the study some experimental results are presented for the case of the classical passive filtering. Preliminary results obtained by simulation, are also presented for the case of active filtering