Abstract: A rotating machine drive system includes a power supply, an electric motor, a rotating machine, a belt drive transmission unit, an electrical information detection sensor, and a diagnostic unit. The electrical information detection sensor detects a current or a voltage. The diagnostic unit calculates estimated rotational speed information of the rotating machine based on the current or the voltage, calculates a reference rotational frequency from a rotational speed of the electric motor and a ratio between a diameter of the electric motor side pulley and a diameter of the rotating machine side pulley. The diagnostic unit uses a difference or a ratio between the estimated rotational speed information and the reference rotational frequency to determine whether or not there is the transmission abnormality.

Abstract: In the invention, it is determined whether or not a transmission abnormality occurs in a belt drive transmission unit including pulleys and a belt which are present between an electric motor and a rotating machine. An electric motor, a rotating machine, and a belt drive transmission unit installed therebetween are provided, and a diagnostic unit is provided which detects a current or a voltage of the electric motor, determines whether or not there is a transmission abnormality of the belt drive transmission unit, based on the current or the voltage, and outputs an abnormality detection signal when it has been determined that there is the transmission abnormality.