 In response , SMRT announced it was replacing important engineering components on all C151 trains by 2019 . This included changing the existing Mitsubishi Electric propulsion system for the newer Insulated @-@ gate bipolar transistor ( IGBT ) and Permanent Magnet Synchronous Motor ( <unk> ) propulsion system by Toshiba , technology currently used in the Tokyo Metro 's 1000 series and 16000 series trains as well as Hankyu 1000 series trains . On 30 July 2015 , trainsets 055 / 056 and 131 / 132 began using this new propulsion system , distinguishable from the original fleet by the whining noise when accelerating or decelerating . In tandem with the replacement of the signalling system on the East @-@ West Line and North @-@ South Line with the newer Thales <unk> signalling system , new equipment had to be installed in the passenger compartment of the trailer cars . 
